Item colors. Why do we see a sheet of paper white and plant leaves green? Why do objects have different colors?

The color of any body is determined by its substance, structure, external conditions and processes occurring in it. These various parameters determine the body's ability to absorb rays of one color falling on it (color is determined by the frequency or wavelength of light) and reflect rays of a different color.

Those rays that are reflected enter the human eye and determine color perception.

A sheet of paper appears white because it reflects white light. And since white light consists of violet, blue, cyan, green, yellow, orange and red, then a white object must reflect All these colors.

Therefore, if on white paper When only red light falls, the paper reflects it, and we see it as red.

Likewise, if only green light falls on a white object, then the object should reflect green light and appear green.

If you touch the paper with red paint, the light absorption properties of the paper will change - now only red rays will be reflected, all others will be absorbed by the paint. The paper will now appear red.

Tree leaves and grass appear green to us because the chlorophyll they contain absorbs red, orange, blue and violet colors. As a result, the middle of the solar spectrum is reflected from plants - green.

Experience confirms the assumption that the color of an object is nothing more than the color of the light reflected by the object.

What happens if a red book is illuminated with green light?

At first it was assumed that green light should turn a book into red: when illuminating a red book with only one green light, this green light should turn red and be reflected so that the book should appear red.

This contradicts the experiment: instead of appearing red, the book appears black in this case.

Since the red book does not turn green into red and does not reflect green light, the red book must absorb green light so that no light is reflected.

Obviously, an object that does not reflect any light appears black. Next, when white light shines on a red book, the book should only reflect red light and absorb all other colors.

In reality, a red object will reflect a little orange and a little purple because the paints used to make red objects are never completely pure.

Likewise, a green book will reflect mostly green light and absorb all other colors, and a blue book will reflect mostly blue light and absorb all other colors.

Let us recall that red, green and blue - primary colors. (About primary and secondary colors). On the other hand, since yellow light is a mixture of red and green, a yellow book must reflect both red and green light.

In conclusion, we repeat that the color of a body depends on its ability to differently absorb, reflect and transmit (if the body is transparent) light of different colors.

Some substances, such as clear glass and ice, do not absorb any color from white light. Light passes through both of these substances, and only a small amount of light is reflected from their surfaces. Therefore, both of these substances appear almost as transparent as air itself.

On the other hand, snow and lather appear white. Further, the foam of some drinks, such as beer, may appear white even though the liquid containing air in the bubbles may be a different color.

Apparently, this foam is white because the bubbles reflect light from their surfaces so that the light does not penetrate deep enough into each of them to be absorbed. Due to reflection from surfaces, soap suds and snow appear white, rather than colorless, like ice and glass.

Light filters

If you pass white light through ordinary colorless transparent window glass, then white light will pass through it. If the glass is red, then light from the red end of the spectrum will pass through, and other colors will be absorbed or filtered.

In the same way, green glass or some other green light filter transmits mainly the green part of the spectrum, and a blue light filter transmits mainly blue light or the blue part of the spectrum.

If you apply two filters of different colors to each other, then only those colors that are transmitted by both filters will pass through. Two light filters - red and green - when folded together, practically no light will pass through.

Thus, in photography and color printing, using light filters, you can create the desired colors.

Theatrical effects created by light

Many of the curious effects which we observe on the theatrical stage are the simple application of the principles with which we have just become acquainted.

For example, you can make a figure in red on a black background almost completely disappear by switching the light from white to a corresponding shade of green.

The red color absorbs the green so that nothing is reflected and hence the figure appears black and blends into the background.

Faces painted with red greasepaint or covered with red rouge appear natural under a red spotlight, but appear black under a green spotlight. The red color will absorb the green color, so nothing will be reflected.

Likewise, red lips appear black in the green or blue light of a dance hall.

The yellow suit will turn bright red in the crimson light. A crimson suit will appear blue in the rays of a bluish-green spotlight.

By studying the absorption properties of different paints, many different other color effects can be achieved.

A team of scientists from Great Britain pleased with a new scientific discovery, presenting the newest type of matter to the general public. Until recently, this type of black shade was unknown to anyone.

The discovered substance is called vantablack and, according to British discoverers, can once and for all change people's understanding of the Universe.

The blackest material absorbs 99.965% of visible light, microwaves and radio waves

Ultrablack material has the ability to successfully absorb 99.96% of light, and in this case we are talking only about radiation that is visible to the human eye. Scientists from Great Britain under the leadership of Ben Jenson began researching the original scientific phenomenon.

According to one of the researchers, the material is composed of an aggregate of carbon nanotubes. This phenomenon can be confidently compared to a human hair cut into 8-10 thousand layers - one such layer is the size of a carbon nanotube. The general composition can be imagined as a field overgrown with grass, where an incident particle of light begins to confidently bounce from one blade of grass to another. These peculiar “blades of grass” absorb light particles as much as possible, reflecting only a small fraction of the light.

The secret of Vantablack is vertically oriented nanotubes

The technology for creating this kind of tube cannot be called innovative, however, Ben Jenson and his associates have only now managed to find worthy ways to use it. They invented a way to connect carbon nanotubes with materials used in modern telescopes and satellites. An example of such a material is aluminum foil. This fact means that photographs Globe and the Universe from space could well be made clearer.

“The presence of stray light inside the telescope increases noise, resulting in less sharp images,” explains Ben Jenson. “By using new materials to coat the internal baffles of the telescope, as well as the diaphragm plates, stray light is reduced and the image is much clearer.”

Given the laws of physics, creating a material that absorbs 100% of light is almost impossible. For this reason alone, Jenson’s invention can today be called a breakthrough on the verge of science fiction.

The American military has already become interested in the new type of material. After all, it can be used in “Stealth” technologies to reduce the visibility of aircraft to radar or create photographs during special reconnaissance missions. In addition, scientists are confident that over time even more opportunities for using vantablack will open up.

The possibility of light decomposition was first discovered by Isaac Newton. A narrow beam of light, passed through a glass prism, was refracted and formed a multi-colored stripe on the wall - a spectrum.

Based on color characteristics, the spectrum can be divided into two parts. One part includes red, orange, yellow and yellow-green colors, the other - green, blue, indigo and violet.

The wavelengths of the visible spectrum rays are different - from 380 to 760 mmk. Beyond the visible part of the spectrum is the invisible part. Parts of the spectrum with wavelengths greater than 780 mmk called infrared, or thermal. They are easily detected by a thermometer installed in this part of the spectrum. Parts of the spectrum with wavelengths less than 380 mmk are called ultraviolet (Fig. 1—see Appendix). These rays are active and negatively affect the light fastness of some pigments and the stability of paint films.

Rice. 1. Spectral decomposition of a color beam

Light rays emanating from different light sources have different spectral composition and therefore differ significantly in color. The light of an ordinary electric light bulb is yellower than sunlight, and the light of a stearin or paraffin candle or kerosene lamp is yellower than the light of an electric light bulb. This is explained by the fact that the spectrum of a daylight beam is dominated by waves corresponding to blue color, and the spectrum of a beam from an electric light bulb with a tungsten and especially a carbon filament is dominated by red and orange color waves. Therefore, the same object can take on different colors depending on what light source it is illuminated with.

As a result, the color of the room and the objects in it take on different color shades under natural and artificial lighting. Therefore, when selecting paint compositions for painting, it is necessary to take into account the lighting conditions during operation.

The color of each object depends on its physical properties, that is, its ability to reflect, absorb or transmit light rays. Therefore, rays of light incident on a surface are divided into reflected, absorbed and transmitted.

Bodies that almost completely reflect or absorb light rays are perceived as opaque.

Bodies that transmit a significant amount of light are perceived as transparent (glass).

If a surface or body reflects or transmits to the same extent all rays of the visible part of the spectrum, then such reflection or penetration of the light flux is called non-selective.

Thus, an object appears black if it absorbs almost all the rays of the spectrum equally, and white if it completely reflects them.

If we look at objects through colorless glass, we will see their true color. Consequently, colorless glass almost completely transmits all the color rays of the spectrum, except for a small amount of reflected and absorbed light, which also consists of all the color rays of the spectrum.

If you replace colorless glass with blue glass, then all objects behind the glass will appear blue, since blue glass transmits mainly blue rays of the spectrum, and almost completely absorbs rays of other colors.

The color of an opaque object also depends on its reflection and absorption of waves of different spectral composition. So, an object appears blue if it reflects only blue rays and absorbs all the rest. If an object reflects red rays and absorbs all other rays of the spectrum, it appears red.

This penetration of color rays and their absorption by objects is called selective.

Achromatic and chromatic color tones. Colors existing in nature can be divided into two groups according to their color properties: achromatic, or colorless, and chromatic, or colored.

Achromatic color tones include white, black and a range of grays in between.

The group of chromatic color tones consists of red, orange, yellow, green, blue, violet and countless colors in between.

A ray of light from objects painted in achromatic colors is reflected without undergoing any noticeable changes. Therefore, these colors are perceived by us only as white or black with a number of intermediate gray shades.

Color in this case depends solely on the body’s ability to absorb or reflect all the rays of the spectrum. The more light an object reflects, the whiter it appears. The more light an object absorbs, the blacker it appears.

There is no material in nature that reflects or absorbs 100% of the light falling on it, so there is neither a perfect white nor a perfect black color. Most White color has a powder of chemically pure barium sulfate, pressed into a tile, which reflects 94% of the light incident on it. Zinc white is somewhat darker than barium sulfate; lead white, gypsum, lithoponic white, premium writing paper, chalk, etc. are even darker. The darkest surface is black velvet, reflecting about 0.2% of light. Thus, we can conclude that achromatic colors differ from each other only in lightness.

The human eye can distinguish about 300 shades of achromatic colors.

Chromatic colors have three properties: hue, lightness, and color saturation.

Hue is the property of color that allows the human eye to perceive and identify red, yellow, blue and other spectral colors. There are many more color tones than there are names for them. The basic, natural range of color tones is the solar spectrum, in which color tones are arranged in such a way that they gradually and continuously transform into one another; red through orange turns into yellow, then through light green and dark green into blue, then into blue and finally into violet.

Lightness is the ability of a colored surface to reflect more or less incident light rays. With more light reflection, the color of the surface appears lighter, with less light it appears darker. This property is common to all colors, both chromatic and achromatic, so any colors can be compared by lightness. For a chromatic color of any lightness it is easy to select an achromatic color similar in lightness.

For practical purposes, when determining lightness, they use the so-called gray scale, which consists of a set of shades of 1 achromatic colors, gradually moving from the most black, dark gray, gray and light gray to almost white. These colors are glued between the holes in the cardboard, and the reflectance of a given color is indicated against each color. The scale is applied to the surface under study and, by comparing it with the color seen through the holes of the scale, the lightness is determined.

The saturation of a chromatic color is its ability to maintain its color tone when various amounts of gray achromatic color, equal to it in lightness, are introduced into its composition.

The saturation of different color tones is not the same. If any spectral color, say yellow, is mixed with light gray, equal to it in lightness, then the saturation of the color tone will decrease somewhat, it will become paler, or less saturated. By further adding light gray to the yellow color, we will get less and less saturated tones, and with a large amount of gray, the yellow tint will become barely noticeable.

If you need to get a less saturated blue color, you will need to introduce a larger amount of gray color, equal in lightness to blue, than in the experiment with yellow color, since the saturation of the spectral of blue color more than spectral yellow.

Purity of hue is the change in brightness of a color under the influence of more or less achromatic light (from black to white). Purity of color tone is of great importance when choosing a color for painting surfaces.

Mixing colors. The perception of the colors that we see around us is caused by the action on the eye of a complex color stream consisting of light waves of different lengths. But we do not get the impression of variegation and multicolor, since the eye has the ability to mix various colors.

To study the laws of color mixing, they use devices that make it possible to mix colors in different proportions.

Using three projection lights with sufficiently powerful lamps and three filters - blue, green and red - you can create a variety of mixed colors. To do this, light filters are installed in front of the lens of each flashlight and the color beams are directed onto a white screen. When pairs of color beams are applied to the same area, three different colors are obtained: the combination of blue and green gives a blue spot, green and red - yellow, red and blue - purple. If you direct all three color beams to one area so that they overlap each other, then by appropriately adjusting the intensity of the light beams using diaphragms or gray filters, you can get a white spot.

A simple device for mixing colors is a spinner. Two paper circles of different colors but the same diameter, cut along the radius, are inserted into one another. This creates a two-color disk in which, by moving the relative positions of the circles, you can change the size of the colored sectors. The assembled disk is put on the axis of the turntable and set in motion. Due to rapid alternation, the color of the two sectors merges into one, creating the impression of a single-color circle. In laboratory conditions, they usually use a turntable with an electric motor having at least 2000 rpm.

Using a turntable, you can get a mixture of several color tones, while simultaneously combining the corresponding number of multi-colored disks

Spatial color mixing is widely used. Colors located close to each other, viewed from a great distance, seem to merge and give a mixed color tone.

Mosaic monumental painting is based on the principle of spatial color mixing, in which the design is composed of individual small particles of multi-colored minerals or glass, giving mixed colors at a distance. The same principle is used for finishing work by rolling multi-colored patterns on a colored background, etc.

The listed methods of mixing colors are optical, since the colors are added or merged into one total color on the retina of our eye. This type of color mixing is called subjunctive or additive.

But mixing two chromatic colors does not always result in a mixed chromatic color. In some cases, if one of the chromatic colors is supplemented with another chromatic color specially selected for it and mixed in a strictly defined proportion, an achromatic color can be obtained. Moreover, if chromatic colors were used, close in purity of color tone to spectral ones, the result will be white or light gray. If the proportionality during mixing is violated, the color tone will be the color of which more was taken, and the saturation of the tone will decrease.

Two chromatic colors that, when mixed in a certain proportion, form an achromatic color are called complementary. Mixing complementary colors can never produce a new color tone. There are many pairs of complementary colors in nature, but for practical purposes, a color wheel of eight colors is created from the main pairs of complementary colors, in which the complementary colors are placed at opposite ends of the same diameter (Fig. 2 - see Appendix).

Rice. 2. Color wheel of complementary colors: 1 - large interval, 2 - medium interval, 3 - small interval

In this circle, the complementary color to red is bluish-green, to orange - blue, to yellow - blue, to yellow-green - violet. In any pair of complementary colors, one always belongs to the group of warm tones, the other to the group of cool tones.

In addition to subjunctive mixing, there is subtractive color mixing, which consists of mechanically mixing paints directly on the palette, paint compositions in containers, or applying two colorful transparent layers on top of each other (glaze).

When mechanically mixing paints, what is obtained is not the optical addition of colored rays on the retina of the eye, but the subtraction from the white ray illuminating our color mixture of those rays that are absorbed by the colored particles of paints. So, for example, when illuminated with a white beam of light on an object painted with a colored mixture of blue and yellow pigments (Prussian blue and yellow cadmium), blue particles of Prussian blue will absorb red, orange and yellow rays, and yellow cadmium particles will absorb violet, blue and cyan rays . Green and similar bluish-green and yellow-green rays will remain unabsorbed, which, reflected from the object, will be perceived by the retina of our eye.

An example of subtractive color mixing is a ray of light passed through three glasses of yellow, cyan and magenta, placed one after the other and directed at a white screen. In places where two glasses overlap - magenta and yellow - you will get a red spot, yellow and cyan - green, cyan and magenta - blue. Where three colors overlap simultaneously, a black spot will appear.

Quantitative color assessment. Quantitative ratings have been established for hue, color purity, and color reflection of light.

Color tone denoted by Greek letter X, is determined by its wavelength and ranges from 380 to 780 mmk.

The degree of dilution of a spectral color, or color purity, is indicated by the letter R. A pure spectral color has a purity of one. The purity of diluted colors is less than one. For example, light orange color is determined by the following digital characteristics:

λ=600 mmk; R = 0,4.

In 1931, the International Commission reviewed and approved a system of graphic color determination, which is still in effect today. This system is built in rectangular coordinates based on three primary colors - red, green and blue.

In Fig. 3, A The International Color Chart is presented, which plots a curve of spectral colors with wavelength λ = 400-700 mmk. In the middle is white. In addition to the main curve, the graph shows nine additional curves that determine the purity of each spectral color, which is established by drawing a straight line from pure spectral color to white. Additional curved lines have digital designations that determine the purity of color. The first curve, located at the white color, has a digital designation of 10. This means that the purity of the spectral color is 10%. The last additional curve has a numerical designation of 90, which means that the purity of the spectral colors located on this curve is 90%.

The graph also contains purple colors that are absent in the spectrum, which are the result of mixing spectral colors violet and red. They have wavelengths with numerical symbols that have a prime.

To determine a color whose digital characteristics are known (for example, λ = 592 mmk, P= 48%), we find on the graph curve a color having a wavelength λ = 592 mmk, draw a straight line from the found point on the curve to the point E, and at the intersection of the straight line with the additional curve marked 48, we put a point, which determines the color that has these digital designations.

If we know the values ​​of the coefficients along the axes X And U, for example along the axis X 0.3 and U 0.4, find the value on the x-axis K= 0.3, and along the ordinate - K= 0.4. We establish that the indicated values ​​of the coefficients correspond to a cool green color with a wavelength λ = 520 mmk and purity of color P = 30%.

Using the graph, it is also possible to determine mutually complementary colors, which are located on a straight line intersecting the entire graph and passing through a point E. Let's say it is necessary to determine a complementary color to orange with a wavelength λ=600 mmk. Drawing a straight line from a given point on a curve through a point E, let's cross the curve on the opposite side. The intersection will be at 490, which denotes a dark blue color with a wavelength of λ = 490 mmk.

In Fig. 3, A(see Appendix) the same graph is presented as in Fig. 3, but made in color.

Rice. 3 International color chart (black and white)

Rice. 3. International color chart (color)

The third quantitative assessment of color is the color reflectance of light, which is conventionally denoted by the Greek letter ρ. It is always less than unity. Reflectance coefficients of surfaces painted or lined with various materials have a huge impact on the illumination of rooms and are always taken into account when designing the finishing of buildings for various purposes. It should be taken into account that as the color purity increases, the reflection coefficient decreases and, conversely, as the color loses its purity and approaches white, the reflection coefficient increases. The coefficient of light reflection of surfaces and materials depends on their color:

Surfaces painted in colors (ρ, % ):

white...... 65—80

cream...... 55—70

straw yellow.55—70

yellow...... 45—60

dark green...... 10—30

light blue...... 20—50

blue...... 10—25

dark blue...... 5—15

black...... 3—10

Surfaces lined ( ρ, % )

white marble...... 80

white brick...... 62

» yellow...... 45

» red...... 20

tiles...... 10-15

asphalt...... 8-12

Certain types of materials ( ρ, % ):

pure zinc white...... 76

pure lithopone...... 75

the paper is slightly yellowish...... 67

slaked lime...... 66.5

Surfaces covered with wallpaper ( ρ, % ):

light gray, sand, yellow, pink, pale blue..... 45-65

dark various colors...... 45

When painting and covering surfaces, colors are usually used that reflect light in the following percentages: on ceilings - 70-85, on walls (upper part) - 60-80, on panels - 50-65; color of furniture and equipment - 50-65; floors - 30-50. Matte colors of the cladding with diffuse (scattered) reflection of light create conditions for the most uniform (without glare) illumination, which ensures normal conditions for the organs of vision.

1 Paintings are small painted areas that serve as samples

Candidate of Chemical Sciences O. BELOKONEVA.

Science and life // Illustrations

Science and life // Illustrations

Science and life // Illustrations

Imagine that you are standing in a sunlit meadow. There are so many bright colors around: green grass, yellow dandelions, red strawberries, lilac-blue bells! But the world is bright and colorful only during the day; at dusk, all objects become equally gray, and at night they become completely invisible. It is the light that allows you to see the world in all its colorful splendor.

The main source of light on Earth is the Sun, a huge hot ball, in the depths of which nuclear reactions are continuously taking place. The Sun sends part of the energy of these reactions to us in the form of light.

What is light? Scientists have debated this for centuries. Some believed that light was a stream of particles. Others conducted experiments from which it was obvious that light behaves like a wave. Both of them turned out to be right. Light is electromagnetic radiation that can be thought of as a traveling wave. A wave is created by oscillations of electric and magnetic fields. The higher the vibration frequency, the more energy the radiation carries. And at the same time, radiation can be considered as a stream of particles - photons. For now, it is more important to us that light is a wave, although in the end we will have to remember about photons.

The human eye (unfortunately, or perhaps fortunately) is capable of perceiving electromagnetic radiation only in a very narrow range of wavelengths, from 380 to 740 nanometers. This visible light is emitted by the photosphere, a relatively thin (less than 300 km thick) shell of the Sun. If we expand "white" sunlight according to wavelengths, you get a visible spectrum - a well-known rainbow, in which the waves different lengths are perceived by us as different colors: from red (620-740 nm) to violet (380-450 nm). Radiation with a wavelength greater than 740 nm (infrared) and less than 380-400 nm (ultraviolet) is invisible to the human eye. The retina of the eye contains special cells - receptors that are responsible for the perception of color. They have a conical shape, which is why they are called cones. A person has three types of cones: some perceive light best in the blue-violet region, others in the yellow-green region, and others in the red.

What determines the color of the things around us? In order for our eye to see any object, it is necessary that the light first hits this object, and only then the retina. We see objects because they reflect light, and this reflected light, passing through the pupil and lens, hits the retina. Naturally, the eye cannot see light absorbed by an object. Soot, for example, absorbs almost all radiation and appears black to us. Snow, on the contrary, evenly reflects almost all the light falling on it and therefore appears white. What happens if sunlight falls on a wall painted blue? Only blue rays will be reflected from it, and the rest will be absorbed. That's why we perceive the color of the wall as blue, because the absorbed rays simply do not have a chance to hit the retina.

Different objects, depending on what substance they are made of (or what paint they are painted with), absorb light in different ways. When we say: “The ball is red,” we mean that the light reflected from its surface affects only those retinal receptors that are sensitive to red color. This means that the paint on the surface of the ball absorbs all light rays except red ones. An object itself has no color; color appears when electromagnetic waves in the visible range are reflected from it. If you were asked to guess what color a piece of paper is in a sealed black envelope, you will not sin at all against the truth if you answer: “No!” And if a red surface is illuminated with green light, it will appear black, because green light does not contain rays corresponding to red color. Most often, a substance absorbs radiation in different parts of the visible spectrum. The chlorophyll molecule, for example, absorbs light in the red and blue regions, and the reflected waves produce green light. Thanks to this, we can admire the greenery of forests and grasses.

Why do some substances absorb green light, while others absorb red? This is determined by the structure of the molecules that make up the substance. The interaction of matter with light radiation occurs in such a way that at one time one molecule “swallows” only one portion of radiation, in other words, one quantum of light or photon (this is where the idea of ​​light as a stream of particles comes in handy for us!). The photon energy is directly related to the frequency of the radiation (the higher the energy, the higher the frequency). Having absorbed a photon, the molecule moves to a higher energy level. The energy of a molecule does not increase smoothly, but abruptly. Therefore, the molecule does not absorb any electromagnetic waves, but only those that are suitable for its “portion” size.

So it turns out that not a single object is colored by itself. Color arises from the selective absorption of visible light by a substance. And since there are a great many substances capable of absorption - both natural and created by chemists - in our world, the world under the Sun is colored with bright colors.

The oscillation frequency ν, the wavelength of light λ and the speed of light c are related by a simple formula:

The speed of light in vacuum is constant (300 million nm/s).

The wavelength of light is usually measured in nanometers.

1 nanometer (nm) is a unit of length equal to one billionth of a meter (10 -9 m).

One millimeter contains a million nanometers.

Oscillation frequency is measured in hertz (Hz). 1 Hz is one oscillation per second.

Chapter 3. Optical properties of paints

Chiaroscuro in painting

Sunlight consists of seven main rays, differing in a certain wavelength and place in the spectrum.

Rays with a wavelength from 700 to 400 mµ, acting on our eyes, cause sensations of one of the colors that we see in the spectrum.

Infrared rays with wavelengths above 700 mµ. do not affect our eyes, and we do not see them.

Ultraviolet rays below 400 mµ are also invisible to our eyes.

If we place a glass prism in the path of a sunbeam, then on a white screen we see a spectrum consisting of simple colors: red, orange, yellow, green, cyan, indigo and violet.

In addition to these seven colors, the spectrum consists of many different shades located between the stripes of these colors and forming a gradual transition from one color to another (red-orange, yellow-orange, yellow-green, green-blue, blue-blue, etc.).

Spectral colors are the most saturated colors and the purest. Of the artistic paints, in terms of purity of tone, ultramarine, cinnabar and yellow chrome are comparatively higher than the others and to some extent approach spectral colors, while most paints seem pale, whitish, cloudy and weak.

Refraction and reflection of light in a paint layer

When light falls on the surface of paintings, part of it is reflected from the surface and is called reflected light, part is absorbed or refracted, i.e. deviates from the original direction by a certain angle, and is called refracted light. Light falling on a flat and smooth surface of a paint layer creates a sensation of shine when the eye is placed in the path of the reflected light.

When the position of the painting changes, i.e., the angle of incidence of the light changes, the shine disappears, and we will enhance the painting well. Paintings with a matte surface reflect light diffusely, evenly, and we do not see glare on them.

The rough surface, with its depressions and protrusions, reflects rays in all possible directions and at different angles from each part of the surface, in the form of tiny sparkles, of which only a small part enters the eye, creating a feeling of dullness and some whitishness. Lacquered oil paints and thickly applied top varnish add shine to the surface of the painting; excess wax and turpentine - dullness.

As is known, color rays, when passing from one medium to another, depending on their optical density, do not remain rectilinear, but at the boundary separating the media, they deviate from their original direction and are refracted.

Rays of light, passing, for example, from air to water, are refracted differently: red rays are refracted less, violet rays are more refracted.

The refractive index of any medium is equal to the ratio of the speed of light in air and the speed in this medium. So, the speed of light in air is 300,000 km/sec, in water about 230,000 km/sec, therefore, the numerical index of refraction of water will be 300,000/230,000 = 1.3, air - 1, oil -1.5.

A spoon in a glass of water seems broken; glass shines more in air than under water, since the refractive gel of glass is greater than that of air. A glass rod placed in a vessel with cedar oil becomes invisible due to the almost identical refractive index of glass and oil.

The amount of reflected and refracted light depends on the refractive indices of the two media separated by the surface. The color of paints is explained by their ability, depending on the chemical composition and physical structure, to absorb or reflect certain rays of light. If the refractive indices of two substances are the same, then there is no reflection; with different indices, some of the light will be reflected, and some will be refracted.

Artist paints are made up of a binder (oil, resin and wax) and pigment particles. Both have different refractive indices, so the reflection inside the paint layer and the color of the paint will depend on the composition and properties of these two substances.

The primer of paintings can be neutral, white or tinted. We already know that light falling on the surface of the paint layer will be partially reflected, partially refracted and passed into the paint layer.

Having passed through pigment particles, the refractive indices of which differ from the refractive indices of the binder, the light is divided into reflected and refracted. The reflected light will be colored and come out to the surface, and the refracted light will pass inside the paint layer, where it will meet pigment particles and will also be reflected and refracted. Thus, the light will be reflected from the surface of the painting in a color complementary to that which is absorbed by the pigment.

We see a variety of colors and shades in nature due to the fact that objects have the ability to selectively absorb different amounts of light falling on them or selectively reflect light.

Every paint light has certain basic properties: lightness, hue and saturation.

Paints that reflect all the rays falling on them in the proportion in which they constitute light appear white. If some of the light is absorbed and some is reflected, the colors appear gray. Black paints reflect the minimum amount of light.

Objects from which more light is reflected appear lighter to us, while less light is reflected from dark objects. White pigments differ in the amount of reflected light.

Barite white has the whitest color.

Barite white reflects 99% of light, zinc white - 94%; lead white - 93%; gypsum - 90%; chalk - 84%.

White, gray and black colors differ from each other in lightness, i.e. in the amount of reflected light.

Colors are divided into two groups: achromatic and chromatic.

Achromatic ones have no color tone, for example, white, gray and dark; chromatic have a color tone.

Colors (red, orange, yellow, green, blue, etc.), except white, gray and dark, reflect a certain part of the rays of the spectrum, mainly the same as its color, which is why they differ in color tone. If you add white or black to red or green, they will be light red and dark red or light green and dark green.

Lightly colored colors hardly differ from gray; on the contrary, strongly colored colors (to which little or no achromatic is mixed) differ significantly from gray in color.

The degree of difference between a chromatic color and an achromatic color of equal lightness is called saturation.

The colors of the spectrum do not contain white, so they are the most saturated.

Paints with fillers (blancfix, kaolin, etc.) and natural pigments (ochre, sienna, etc.), reflecting a large number of rays, similar in composition to white, have a dull and whitish, i.e., weakly saturated tone.

The more fully the paint reflects certain rays, the brighter its color will be. Any paint mixed with white becomes paler.

There are no paints that would reflect only a ray of one color and absorb all the others. Paints reflect composite light with a predominance of the ray that determines its color, for example, in ultramarine this light will be blue, in chromium oxide it will be green.

Additional colors

When illuminating the paint layer, some of the rays are absorbed, some more, others less. Therefore, the reflected light will be colored in a complementary color to the one that was absorbed by the paint.

If the paint absorbs orange rays from the rays falling on it and reflects the rest, then it will be colored blue, if red is absorbed - green, if yellow is absorbed - blue.

We are convinced of this by simple experiment: if we place another prism in the path of the decomposition of rays by a glass prism and move it sequentially along the entire spectrum, deflecting individual rays of the spectrum to the side, first red, orange, yellow, yellow-green, green and bluish-green, then the color of the mixture of the remaining rays will be colored bluish-green, blue, blue, violet, purple and red.

By mixing these two components (red and green, orange and blue, etc.), we again get white.

White color can also be obtained by mixing a pair of separate spectral rays, for example, yellow and blue, orange and cyan, etc.

Simple or complex colors that produce white when optically mixed are called complementary colors.

For any color, you can choose another color, which, when optically mixed, gives an achromatic color in certain quantitative ratios.

Additional primary colors will be:

Red Green.

Orange - blue.

Yellow - blue.

In the color wheel, which consists of eight color groups, complementary colors are located opposite each other.

When two non-complementary colors are mixed in certain quantitative ratios, colors that are intermediate in tone are obtained, for example: blue with red produces violet, red with orange produces red-orange, green with blue produces green-blue, etc.

Intermediate colors: violet, crimson, red-orange, yellow-orange; yellow-green, green-blue, blue-blue.

We can arrange the main and intermediate colors of the spectrum in order in the following row:

No. 1a Raspberry

No. 1 Red

No. 2a Red-orange

No. 2 Orange

No. For Yellow-Orange

No. 3 Yellow

No. 4a Yellow-green

No. 4 Green

No. 5a Green-blue

No. 5 Blue

No. 6a Blue

No. 6 Blue

No. 7a Violet

Additional intermediate colors:

Purple and crimson-yellow-green.

Red-orange - green-blue.

Yellow-orange - blue-blue.

Additional primary and intermediate colors are three numbers apart.

Transparent and opaque paints.

Paints that absorb part of the light and transmit part are called transparent, and those that only reflect and absorb are called opaque, or opaque.

Transparent or glaze paints include those paints whose binder and pigment have equal or similar refractive indices.

Transparent artistic oil paints usually have a refractive index of the binder and pigment of 1.4-1.65.

When the difference between the refractive indices of the pigment and the binder is not higher than 1, the paint reflects little light at the interface; most of the light passes deep into the paint layer.

Due to selective absorption by pigment particles, light is intensely colored along its path and, when it hits the ground, returns back to the surface of transparent substances.

In this case, the primer is prepared white and matte so that it reflects the rays more fully.

Larger pigment particles in paint provide increased transparency.

Transparent paints are of great value for painting compared to opaque ones, since they have a deep tone and are the most saturated.

Transparent paints include:

Refractive indices

Kraplak 1.6-1.63

Ultramarine 1.5-1.54

Cobalt blue 1.62-1.65

Blanfix 1.61

Alumina 1.49-1.5

When illuminating, for example, transparent green paint with daylight, part of the mainly red, i.e. additional, rays will be absorbed, a small part will be reflected from the surface, and the remaining not absorbed will pass through the paint and undergo further absorption. Light not absorbed by the paint will pass through it, and then be reflected, come to the surface and determine the color of the transparent object - in this case, green.

Covering inks include those in which the refractive indices of the binder and pigment have a large difference.

Light rays are strongly reflected from the surface of the opaque paint and even in a thin layer they are not very transparent.

Covering oil paints, when mixed with transparent mixtures, take on various shades that captivate artists with their depth and transparency compared to the dull whites of zinc or lead white.

The most opaque are adhesive paints - gouache, watercolor and tempera, since after the paint dries, the space in it is filled with air with a lower refractive index compared to water.

Covering inks include: lead white (refractive index 2), zinc white (refractive index 1.88), chromium oxide, cadmium red, etc.

Mixing colors.

Mixing paints is used to obtain different color shades.

Typically, three mixing methods are used in practice:

1) mechanical mixing of paints; 2) applying paint to paint; 3) spatial mixing;

Optical changes when mixing paints can be clearly understood using the example of daylight passing through yellow and blue glasses sequentially.

Light, passing first through yellow glass, will lose almost entirely the blue and violet colors and will pass through blue-green, green, yellow-green, yellow, orange and red, then blue glass will absorb red, orange and yellow and let through green ones, therefore, when passing Light through two colored glasses absorbs all colors except green.

Typically, pigments absorb colors close to the complementary color.

If, having prepared a mixture of yellow cadmium with blue cobalt on the palette, we apply them to the canvas, then we will be convinced that the light falling on the paint layer of this mixture, passing through the yellow cadmium, will lose blue and violet rays, and passing through the blue paint will lose red ones, orange and yellow rays. As a result, the reflected light and the color of the paint mixture will be green.

Mixed paint is darker than any one paint taken for mixing, since the mixed paints contain other colors besides green. Therefore, it is impossible to get a very intense light green - pol veronese - by tinting.

Cinnabar with Prussian blue produces a gray paint. Kraplak with Prussian blue, cobalt blue and ultramarine form good violet shades, since kraplak contains more violet than cinnabar and, therefore, is more suitable for mixing with blues.

The method of applying one layer of transparent paint to another in order to obtain different shades is called glazing.

When glazing, the top layers of paint must be transparent so that the bottom layer or primer can be seen through them.

As with a single layer, the light illuminating a painting in a multi-layer painting will have the same reflection and absorption phenomena as in the previous example with a mixture of yellow and blue paints.

It should be noted that depending on the covering properties of the paints, the thickness of the paint layer and the order of application, one or another reflected light will prevail.

So, if yellow and blue colors are transparent, then most of the light will be reflected from the ground and the reflected light will be closer to green.

If yellow topcoat is placed on top of the paint layer, the predominant amount of light will be reflected from the top yellow layer and the color of the mixture will be closer to yellow.

As the thickness of the top yellow paint layer increases, the light will travel a long way and become more intense.

By changing the order of the paints (for example, blue paint will be on top and yellow will be below), the light reflected from the first layer will be blue, in the bottom layer it will be blue-green and reflected green from the ground, resulting in the color of the entire paint layer being blue-green.

When viewing two small surfaces of different colors at a great distance, our eye is not able to see each color separately, and they merge into one common color.

Thus, at some distance we also see sand as one color, despite the fact that it consists of countless multi-colored grains of sand.

The mosaic, which is made up of small pieces of colored stones (smalt), is based on spatial mixing. In painting, small specks and dashes of different colors give a wide variety of shades when viewed from a distance.

The spatial mixing method increases the lightness of the colors. So, if one or two thin strips of white are drawn in a red stripe, then the red stripe will receive bright illumination, which cannot be achieved by mixing with white. This technique significantly changes the intensity of the colors (increases or decreases). Artists can almost easily obtain the desired tone from a mixture of paints.

The rays of light reflected by individual colored dots go so close to each other that our organ of vision perceives them by the same light-sensitive nerve ending (cone) and we see one common color, as if the paints were actually mixed.

When mixing colors we get the impression general color from the reflection of various rays, since the eye does not distinguish the individual components of the mixture due to their small size.

Color contrasts.

Looking at two small painted surfaces lying next to each other, one orange and the other gray, the latter will appear bluish to us.

It is well known that blue and orange colors, when combined, changing in tone, mutually increase in brightness; the same pairs of colors that increase in brightness will be yellow and blue, red and green, violet and yellow-green.

A change in color under the influence of painted surfaces lying nearby is called simultaneous contrast and is a consequence of irritation by light of three nerve centers of the eye independent of each other.

Paints placed on the canvas change their color depending on the color of the paints located near them (for example, gray turns blue against a background of yellow, and blue turns yellow). If you put paint on a background that is lighter in color, the paint will seem darker, and on a darker background, on the contrary, it will seem lighter. Green paint on a red background becomes brighter; whereas the same paint, placed on a greenish background, will appear dirty due to the action of the additional colorful color. As a rule, paints that are similar in color reduce the intensity of the tone.

If, after looking at one color surface for a long time, the gaze is transferred to another, then the perception of the second will to a certain extent be determined by the color of the first surface (after a dark first surface, the second surface will appear lighter, after red, white will appear greenish).

The eye appears as a contrasting color, close in shade to the complementary color.

Complementary to blue is yellow, and contrasting is orange; complementary to violet is yellow-green, and contrasting is yellow.

The change in the perception of color depending on what color acted on the eye before is called sequential contrast.

By placing separate pairs of colors next to each other, their shades change as follows:

1. Yellow and green: yellow takes on the color of the one preceding it in the spectrum,

i.e. orange, and green is the color of the subsequent one, i.e. blue.

2. Red and yellow: red changes to purple and yellow to yellow

3. Red and green: complementary colors do not change, but are enhanced in

brightness and tone saturation.

4. Red and Blue: Red becomes orange and blue gets closer to

green, i.e. two colors separated in the spectrum by two or more numbers take on the color

additional neighbor.

Knowing and using color contrast techniques, you can change the tone of the colors and color of the picture in the desired direction.

Along with color contrasts, the reproduction of space and depth of the picture is of great importance in painting.

In addition to perspective construction, the depth of the picture can be achieved by placing colors: dark colors create the illusion of depth; bright colors, light places come to the fore.

To achieve high light and color intensity of paints and obtain a variety of shades, artists use the technique of mutual influence of paint colors (color contrast), placing them in certain spatial relationships.

If you put a small spot of white paint on a black background, the white spot will appear the lightest, while the same white spot on a gray background will appear dark. This contrast is more pronounced when the background lightness differs significantly from the color of the paints. In the absence of such a contrast in lightness, nearby paints that are similar in shade appear dull. In the paintings of great masters, reflections of light surrounded by dark tones create the impression of very bright and light colors.

In addition to lightness contrast, there is color contrast. Two paints placed next to each other influence each other, causing a mutual change in their shades towards the complementary color.

The influence of lighting on the color of paints.

The paint layer, depending on the lighting, takes on various shades during the day, since sunlight, under the influence of many reasons, modifies its spectral composition.

Depending on the nature of the light source, the color of the paint may vary. Under artificial light, cobalt blue appears greenish due to the presence of yellow rays in the light; ultramarine - almost black.

The color of the paint also depends on the shade of the light source, for example, with cold lighting, cold colors become brighter. The color of paints darkens when exposed to light that is opposite in tone: orange from blue, violet from yellow.

Cobalt blue becomes gray under artificial lighting and acquires brightness and depth of color in daytime sunlight, on the contrary - cadmium yellow, red kraplak and cinnabar appear brighter under artificial lighting.

Based on a number of experiments, it was established that when illuminated with kerosene, yellow, orange, red and generally all warm colors increased in tone, while cold colors (blue and green) decreased, i.e. darkened.

Chromium oxide becomes gray-green, cobalt blue takes on a violet hue, ultramarine becomes cloudy, Prussian blue turns green, etc.

Consequently, when the nature of the lighting source changes in paintings, such strong optical changes appear that the relationships between tones and the overall color of the painting are completely disrupted, since artificial lighting has a different composition of rays (yellow and orange rays), very different from the composition of daylight rays. The influence of artificial light on the shade of paints has been perfectly proven by experiments conducted by Prof. Petrushevsky. (S. Petrudpevsky. Paints and painting, St. Petersburg, 1881, pp. 25-36.)

Colors of translucent, cloudy media

Dusty air, smoke, fog, muddy water, milk, foam, etc. are usually called turbid media in which the smallest particles of a solid or gaseous substance are suspended.

Dusty air and smoke are like a homogeneous mixture of air and solid particles; milk-water and tiny drops of butter; fog-air and water droplets; foam - water and air. Characteristic property Such mixtures or turbid media have the ability to reflect part of the light and transmit part of it.

Short-wave rays of light (blue and violet), falling on tiny suspended particles - solid (smoke), liquid (fog) or gaseous (foam) - almost the same size as the wavelength, are reflected and scattered in all directions, and we see blue or blue light.

Longer wavelength rays (red, orange and yellow) pass freely through tiny suspended particles, turning the light dark.

A mass of tiny solid and liquid particles is carried in the air, therefore in the evening, as the sun approaches the horizon, its rays (red, orange and yellow, i.e. with a longer wavelength), passing through a large layer of polluted air, are colored Orange color.

We also observe a similar phenomenon on foggy days:

High air humidity enhances the color of the sun at sunset. By mixing a small amount of opaque paint with a binder (oil or varnish), we obtain translucent paints. Applied to a dark surface, they become cold; when applied to a light surface, they become warmer for the same reasons mentioned above.

Reflexes.

Reflexes, or colored colors of light, are the result of reflection of it by illuminated objects standing close to each other.

Colored light reflected from the first object falls on another object, this produces selective absorption and a change in color tone.

If light falls on the folds of matter, then the protruding parts, illuminated directly by the light source, acquire a color that differs from the color of the depressions.

Colored light reflected by the fabric falls inside the folds, it will be darker, but part of the light after reflection again penetrates deep into the folds, and the color of the folds in the depths will be richer and darker than on the protruding parts.

Depending on the spectral composition of light and selective absorption, the color tone changes (for example, yellow matter deep in the folds sometimes has a greenish tint).

Chiaroscuro in painting.

The arrangement of light on objects in different strengths is called chiaroscuro. The phenomenon of chiaroscuro depends on the overall intensity of illumination and the color of objects. If the lighting in the shadow is ten times weaker, then all paints, regardless of color, being in the shadow will reflect ten times less light than the same paints in the light.

The light reflected by objects in the shadow is reduced evenly, and the ratio between the colors of objects in the shadow does not change, only a general decrease in color brightness occurs.

When rendering shadows, they sometimes use black tones mixed in with paints, but then, instead of the impression of a shadow, the impression of dirt is created, since in the shadow a decrease in brightness occurs with a uniform darkening of all colors.

Light shadows in bright light are more noticeable on dark-colored objects; on light-colored objects they are whitish and very faint in tone.

Light objects with deep shadows appear more saturated.

In very dense shadows, only the lightest objects retain color differences, while the darkest ones merge with each other.

In low light, colors become less saturated.

Chiaroscuro plays a big role in building the volume of a form. Typically, highlights are painted solidly, while shadows and penumbras are painted transparently.

With an excessive abundance of light or a lack of it, objects are almost indistinguishable, and the volume is almost not felt. The lighting in the picture is kept mainly at medium strength.

Some old masters used double lighting techniques: brighter for the main figures and weaker for the secondary ones, which made it possible to depict the main figures in relief and convexity, in a rich color scheme; the background is poorly lit, and there are almost no color shades in it.

The technique of double lighting allows you to focus the audience's attention on the main figures and create the impression of depth.

The skillful use of chiaroscuro gives very effective results in painting practice.