Whitewash, types and their characteristics. Whiteness rating Scale of lightness of natural hair shades

All non-luminescent (non-self-luminous) materials, including white pigments and paints, unlike an ideal white surface, do not have a reflectance coefficient for all wavelengths of visible light and, due to the selective absorption of different wavelengths of light, have a specific color tone. The color tone of white pigments, characterized by low saturation, is called color tint.

The whiteness index is a quantitative assessment of the visual perception of the whiteness of a material, taking into account its shade. Whiteness is the degree to which a color approaches ideal white. A surface that diffusely reflects all light incident on it in the entire visible region of the spectrum (ideal MgO diffuser) is called ideally white.

The human eye distinguishes even very small differences in color shades and lightness of two closely spaced compared white surfaces, but cannot quantify their whiteness.

It is known and widely used to increase the whiteness of the material by bluing. At the same time, the intensity of the long-wave, yellowish-reddish component in the spectrum of diffuse reflected radiation decreases, but the brightness of the sample of the material being blued also decreases, a gray tint appears, but the visually perceived whiteness sharply increases.

The instrumental method of measuring whiteness is subject to the same requirements as the instrumental method of measuring color characteristics - full compliance of the measured value with its visual perception. The difficulty of the instrumental method lies in determining the influence of shade white to its whiteness.

When assessing the whiteness of white surfaces that differ in color shade and lightness, the best results are obtained by the colorimetric method. Using the colorimetric method, results that are closest to visual are obtained by comparing the whiteness of surfaces with different color tones and lightness according to the number of color discrimination thresholds. The color threshold is the smallest difference in hue and lightness perceived by the eye. According to the Weber-Fichner law, in order to obtain the same difference in color tone and lightness perceived by the eye, it is necessary to change them in geometric progression.

Most often, to assess the whiteness of white pigments, the values of the color differences between the measured sample and the accepted standard are used. Whiteness W in this case is calculated by the formula:

W=100- ∆E

Where ∆E – complete color difference.

The MKO whiteness formula is written as an equation:

where are the chromaticity coordinates of the achromatic point for the selected observer (2 0 or 10 0), always with D65 radiation, since the assessment of luminescent white colors under any other illumination does not make sense. The higher the W value, the higher the whiteness of the sample. For a completely reflective diffuser, the whiteness value is W=100. samples containing luminescent brighteners may have values of W>>100. a barely perceptible difference noticeable by a qualified assessor upon visual assessment is equivalent to 3 ICE whiteness units.

Ganz and Griesser proposed a general formula for determining shade ( Тw) samples whose color is perceived as white:

where x and y are the chromaticity coordinates of the sample. The coefficients m, n and k can be varied, allowing the formula to be used to simulate different scales for visual hue assessment.

Also in 1982, the ICE adopted the equation:

where a = 1000 for D65/2 and equals 900 for D65/10.

For neutral whites, including a perfect reflective diffuser, Tw=0. if Tw >0, the sample is perceived as greenish-white; if Tw<0, то он красноватого оттенка .

In scientific color science, the term “whiteness” is also used to assess the lightness qualities of a surface, which, in our opinion, is of particular importance for the practice and theory of painting. The term “whiteness” in its content is close to the concepts of “brightness” and “lightness”, however, unlike the latter, it contains a connotation of a qualitative characteristic and even, to some extent, aesthetic.

What is whiteness? R. Ivens explains this concept as follows: “If lightness characterizes the perception of brightness, then whiteness characterizes the perception of reflectivity.” The more a surface reflects the light falling on it, the whiter it will be, and theoretically, an ideal white surface should be considered a surface that reflects all rays falling on it; however, in practice such surfaces do not exist, just as there are no surfaces that would completely absorb the light incident on them. In practice, we call surfaces that reflect different amounts of light white. For example, we rate chalk soil as white soil, but as soon as you paint a square on it with zinc white, it will lose its whiteness. If we then paint the inside of the square with white that has even greater reflectivity, for example barite, then the first square will also partially lose its whiteness, although we will practically consider all three surfaces to be white. It turns out that the concept of “whiteness” is relative, but at the same time there is some kind of boundary from which we begin to consider the perceived surface to be no longer white.

The concept of whiteness can be expressed mathematically. The ratio of the light flux reflected by a surface to the flux incident on it (in percentage) is called “albedo” (from Latin albus - white). This relationship for a given surface is generally maintained under different lighting conditions, and therefore whiteness is a more constant quality of a surface than lightness. For white surfaces, the albedo will be 80-95%. The whiteness of various white substances can thus be expressed in terms of their reflectivity. V. Ostwald gives the following table of the whiteness of various white materials:

Barium sulfate (barite white) - 99%
Zinc white – 94%
Lead white - 93%
Gypsum - 90%
Fresh snow - 90%
Paper - 86%
Chalk - 84%

A body that does not reflect light at all is called an absolute black body in physics. But the blackest surface we see will not be completely black from a physical point of view. Since it is visible, it reflects at least some amount of light and thus contains at least a negligible percentage of whiteness - just as a surface approaching ideal white can be said to contain at least a negligible percentage of blackness. We consider a surface to be practically black, in the perception of which details are indistinguishable due to the lack of physical stimulus. White and gray in nature have superficial qualities, and gray, the darker it is, to a lesser extent. Black is devoid of these qualities. Ivens defines the difference between white, gray and black as follows: “White is a phenomenon related entirely to the perception of surface; gray is the perception of the relative lightness of the surface, and black is the positive perception of the insufficiency of the stimulus to provide the proper level of vision.”

In the practice of painting, the concept of black is also very relative. The blackest spot in a painting has some whiteness and color tone. Various black colors, which can be mistaken for extreme blackness, turn out to be so only when perceived in isolation; when compared with each other, they, in addition, always reveal different color shades. Van Gogh, for example, counted up to 27 different black colors from Frans Hals. We almost never encounter purely achromatic black. The color of black paint is the standard of black for the artist, and the experience he has acquired in perception makes it possible to correlate all other tones with this blackness.

You can find another name for this paint, for example: silicon white, Flemish white, French white. The base of this paint is lead carbonate (PW 1). Despite its toxicity, this paint is still the most favorite among white oil paints. Modern lead white, of course, is no longer what it was in the old days. Although the main task of technologists remains the preservation of all the properties that this paint had and due to which it was so valued by great masters.
Lead white is capable of creating a thin, durable, elastic film that has the highest degree of light fastness. The paint is matte and very durable. Lead speeds up drying time in whitewash + oil paint mixtures.
True, lead white does not tolerate mixtures with many paints: with cobalt blue and light violet, coput-mortuum, red kraplak and ultramarine, a darkening of the tone is possible over time, and with dark cobalt violet, manganese blue, dark ocher, dark and light mars brown highlighting tone. A layer of varnish applied to the dried film prevents it from darkening.
Light fastness: 1.
Oil Absorption: very low.
Film: dries very quickly, hard, elastic.
Toxicity: extremely toxic.

Titanium white.

These paints are based on pigments: titanium oxide, titanium dioxide or titanium barium - and are gradually replacing lead white. Previously, these whites had problems with film strength and were always used with zinc oxide. In some studies that have survived to this day, one can find a warning that titanium does not react with oil and does not create a mixed paste. Modern pigments are able to create a stronger film that better resists heat, light and atmospheric agents. Titanium white has the highest degree of color retention of all available whites. They are the most matte and very durable. But there is still a drawback: the paint creates a slow-drying and brittle film.
Light fastness: 1.
Oil Absorption: low.
Film: dries slowly and becomes brittle.
Toxicity: non-toxic.

Zinc white,

or Chinese white, snow white. Zinc oxide (PW 4). Paints appeared in 1751 and began to be produced in 1850. This white is translucent and has an average degree of color intensity retention. They are characterized by a cold tone. Very durable, but dries slower than white lead. In mixtures with almost all paints they do not change over time. The exception is a mixture with violet speck, which brightens the tone. Creates an inelastic film. Unlike lead white, zinc white does not turn yellow when it comes into contact with sulfur vapor (there is enough of it in the atmosphere).
Light fastness: I.
Oil Absorption: very low.
Film: dries slowly, hard, brittle
Toxicity: non-toxic.

Silver whitewash. A non-standard term used for both lead and zinc white. The French term blanc d'argent (white color of money) implies lead white.
Blend whites. As with black paints, manufacturers created complex mixtures of white pigments. A common combination is a mixture of titanium and zinc.
Sublimated lead white. It is lead sulfate which contains zinc. This white has the characteristics of lead white (PW1), but is of lower quality. This concerns oil absorption and strength of mixtures with other pigments. They are superior to lead white in terms of dullness, are not as toxic and darken less when exposed to sulfur fumes.

Magazine "ARTindustry"

White paints are used in painting, decoration, construction and everyday life. Zinc and titanium whitewash have found application in all areas of artistic activity related to the creation of a paint layer on the surface of a product or canvas. In construction, white is used for painting surfaces and as a pigment for some water-soluble paints.

White paints and the history of their creation

Much earlier than the advent of zinc white, humanity learned to make lead white. This type of paint was known to the ancient Greeks and Romans. Lead white was used everywhere until the 19th century.

Due to the toxicity of lead-based white paint, humanity has not given up attempts to create alternatives. This is how zinc white was invented. But, having appeared in 1780, they did not become widespread due to the high cost of their production process, and only 60 years later relatively cheap zinc-based white paints were obtained.

Following this, titanium white was discovered in 1912. These paints first appeared in Norway. Titanium white differs from other white paints in that it is completely non-toxic and has good covering properties.

Thus, new titanium and zinc compositions have replaced lead white.

Characteristics of white paints

Zinc white goes on sale in the form of ready-made or thickly rubbed paints. Thickly ground materials must be diluted with oil varnish before use. Other thinners are not suitable for this purpose, since as a result the painted surface will acquire a yellowish tint.

This material in its pure form is characterized by a snow-white color with a bluish tint. The quality and whiteness of this material depends entirely on the raw materials from which the pigment was obtained. This product should be stored covered, as it absorbs moisture from the environment. Zinc white pigments do not ignite and do not deteriorate under the influence of microorganisms.

This coloring material has a lot of positive qualities:

Good resistance to direct sunlight.
High level of compatibility with many colors in the colorful palette.
Possibility of application in all areas of painting and decorative arts.
Low toxicity.

Zinc white has negative qualities:

takes a long time to dry;
have low hiding power;
the paint layer created by whitewash is prone to cracking;
require large consumption of oil solvents.

Thickly ground white is used to obtain colorful compositions for coating wooden, metal and plastered surfaces of walls and ceilings.

Lead white had a pure snow-white color that did not lose its brightness when exposed to sunlight. The positive qualities of these paints include:

plasticity, which allowed the paint to remain strong and not crumble, even if it became necessary to roll up the canvas;
good resistance to moisture;
the ability to quickly dry the paint layer after application to the surface.

Lead white has disadvantages that have caused it to become less popular:

high toxicity;
not mixed with all paints;
Over time, the paint layer loses its brightness.

All these negative aspects have led to the fact that lead white is not used for industrial purposes.

Titanium white is advantageous because it:

create a matte and very durable surface;
able to withstand exposure to atmospheric moisture and direct rays of light;
have the highest brightness of all modern white paints.

Titanium compounds have one drawback: when dry, they create a brittle surface of the paint layer.

Alkyd paints were the latest to appear; they are the product of a complex chemical synthesis.

Application

Due to its high toxicity, lead white is not used in everyday life. To paint surfaces in order to isolate them from moisture, oil-based zinc white, alkyd and titanium compounds are used.

For painting plastered walls and ceilings, water-soluble paints based on zinc white are used. It should be noted that walls are now rarely painted white; most often this paint is used to cover the ceiling.

Sequence of painting work

The ceiling is painted as follows:

The first thing that needs to be done even before starting painting work is to put on protective goggles over your eyes, and gloves on your hands; you should also cover your hair with a scarf or cap (this is done in order to avoid paint dripping from the ceiling from getting into your eyes and on the hair).
It is necessary to provide air access to the room. After painting, the room should be well ventilated.
Clean the ceiling from layers of old cracked and falling off plaster, paint, dust, grease, and drips.
Apply new layers of plaster and level the ceiling. Painting is carried out only on a perfectly flat surface.
The putty surface is sanded with sandpaper until the ceiling reaches the desired smoothness.
The surface, which has increased absorption properties, is covered with two layers of drying oil. The primer layers are allowed to dry between coats.

Painting metal products with white paints

There are two industrial methods of applying whitewash of any kind to the surface of metal products. The first of them involves completely immersing a metal part in a container containing zinc or titanium white (lead white is not used for industrial purposes).

The second method of industrial painting of a metal surface involves applying a paint layer of zinc, alkyd or titanium compositions to the entire area of the product using a spray gun. For this purpose, solvents are added to the paints in the required quantities, after which the coloring composition is filtered. Only after this can you begin to apply the paint coating.

In everyday life, painting is done using a roller or brush (cars cannot be painted in this way). Also, lead white is not used for painting household items.

Coloring materials must be stirred before use. If they have thickened, you can add natural drying oil or zinc white to the zinc white. Oil paints are diluted with white spirit, turpentine or a special solvent for oil paints (all this can be purchased at specialized stores that sell goods for artists).
Paints are applied to a primed surface.
High-quality painting can be achieved by applying two layers of paint.
A new layer of paint is applied only to a well-dried surface, otherwise the film formed by the previous layers will be damaged.
If lead white is used in artistic activities, it is necessary to take precautions and periodically ventilate the room.

White paints are used in everyday life more often than others.

This is due to the fact that they are mixed with other colors to create the necessary shades. It is important to remember that you should only combine materials that are created on the same basis.

The retina consists of two types of light-sensitive cells - rods and cones. During the day, in bright light, we perceive the visual picture and distinguish colors using cones. In low light, rods come into action, which are more sensitive to light, but do not perceive colors. That is why at dusk we see everything in gray, and there is even a proverb “At night all cats are gray.”

Because there are two types of light-sensitive elements in the eye: cones and rods. Cones distinguish colors, but rods distinguish only the intensity of light, that is, they see everything in black and white. Cones are less sensitive to light than rods, so in low light they cannot see anything at all. The rods are very sensitive and react even to very weak light. That is why in semi-darkness we cannot distinguish colors, although we see contours. By the way, cones are mainly concentrated in the center of the visual field, and rods are at the edges. This explains the fact that our peripheral vision is also not very colorful, even in daylight. In addition, for the same reason, astronomers of past centuries tried to use peripheral vision when making observations: in the dark it is sharper than direct vision.

35. Is there such a thing as 100% white and 100% black? In what units is whiteness measured??

In scientific color science, the term “whiteness” is also used to evaluate the light qualities of a surface, which is especially important for the practice and theory of painting. The term “whiteness” in its content is close to the concepts of “brightness” and “lightness”, however, unlike the latter, it contains a connotation of qualitative characteristics and even, to some extent, aesthetic.

What is whiteness? White characterizes the perception of reflectivity. The more a surface reflects the light falling on it, the whiter it will be, and theoretically, an ideal white surface should be considered a surface that reflects all rays falling on it, but in practice such surfaces do not exist, just as there are no surfaces that would completely absorb the incident light. them light.

Let's start with the question, what color is the paper in school notebooks, albums, books?

You probably thought, what kind of an empty question is this? Of course white. That's right - white! Well, what kind of paint were the frame and window sill painted? Also white. Everything is correct! Now take a notebook sheet, a newspaper, several sheets from different albums for drawing and drawing, put them on the windowsill and carefully examine what color they are. It turns out that, being white, they are all different colors (it would be more correct to say different shades). One is white-gray, another is white-pink, the third is white-blue, etc. So which one is “pure white”?

In practice, we call surfaces that reflect different amounts of light white. For example, we rate chalk soil as white soil. But if you paint a square on it with zinc white, it will lose its whiteness, but if you then paint the inside of the square with white that has an even greater reflectivity, for example barite, then the first square will also partially lose its whiteness, although we will practically consider all three surfaces white .

It turns out that the concept of “whiteness is relative, but at the same time there is some kind of boundary from which we begin to consider the perceived surface to be no longer white.

The concept of whiteness can be expressed mathematically.

The ratio of the luminous flux reflected by a surface to the flux incident on it (in percentage) is called “ALBEDO” (from Latin albus - white)

ALBEDO(from Late Latin albedo - whiteness), a value characterizing the ability of a surface to reflect a flow of electromagnetic radiation or particles incident on it. Albedo is equal to the ratio of the reflected flux to the incident flux.

This relationship for a given surface is generally maintained under different lighting conditions, and therefore whiteness is a more constant surface quality than lightness.

For white surfaces, the albedo will be 80 - 95%. The whiteness of various white substances can thus be expressed in terms of reflectance.

W. Ostwald gives the following table of the whiteness of various white materials.

In physics, a body that does not reflect light at all is called absolutely black. But the blackest surface we see will not be completely black from a physical point of view. Since it is visible, it reflects at least some amount of light and thus contains at least a negligible percentage of whiteness - just as a surface approaching ideal white can be said to contain at least a negligible percentage of blackness.

CMYK and RGB systems.

RGB system

The first color system we'll look at is the RGB system (from "red/green/blue" - "red/green/blue"). A computer or TV screen (like any other body that does not emit light) is initially dark. Its original color is black. All other colors on it are obtained by using a combination of these three colors, which in their mixture should form white. The combination “red, green, blue” - RGB (red, green, blue) was experimentally derived. There is no black color in the scheme, since we already have it - this is the color of the “black” screen. This means that the absence of a color in the RGB scheme corresponds to black.

This color system is called additive, which roughly translates to “additive/complementary.” In other words, we take black (the absence of color) and add primary colors to it, adding them together to white.

CMYK system

For colors that are obtained by mixing paints, pigments or inks on fabric, paper, linen or other material, the CMY system (from cyan, magenta, yellow) is used as a color model. Due to the fact that pure pigments are very expensive, to obtain black (the letter K stands for Black) color, not an equal mixture of CMY is used, but simply black paint

In some ways, the CMYK system works completely opposite to the RGB system. This color system is called subtractive, which roughly translates to “subtractive/exclusive”. In other words, we take the color white (the presence of all colors) and, by applying and mixing paints, we remove certain colors from white until all colors are completely removed - that is, we get black.

The paper is initially white. This means that it has the ability to reflect the entire spectrum of colors of light that hits it. The better the quality of the paper, the better it reflects all colors, the whiter it seems to us. The worse the paper, the more impurities and less white it contains, the worse it reflects colors, and we consider it gray. Compare the paper quality of a high-end magazine and a cheap newspaper.

Dyes are substances that absorb a specific color. If a dye absorbs all colors except red, then in sunlight, we will see a “red” dye and consider it “red paint.” If we look at this dye under the light of a blue lamp, it will turn black and we will mistake it for “black dye”.

By applying different dyes to white paper, we reduce the number of colors it reflects. By painting paper with a certain paint, we can make it so that all the colors of the incident light will be absorbed by the dye except one - blue. And then the paper will seem to us to be painted blue. And so on...Accordingly, there are combinations of colors, by mixing which we can completely absorb all the colors reflected by the paper and make it black. There is no white color in the scheme, since we already have it - it is the color of paper. In those places where white is needed, the paint is simply not applied. This means that the absence of a color in the CMYK scheme corresponds to white.