A pigment is a chemical compound that changes the color of a substance to be colored. Such a hue change effect is based on a change in the composition of the base, as a result of which the length of the light wave reflected from the painted object is adjusted. This physical process should not be confused with fluorescence, phosphorescence and other forms of luminescence in which the material itself emits light.
What is pigment and how does it work?
Pigments are coloring matter. Unlike dyes, they consist of particles and are practically insoluble in the medium to be painted. The medium to be painted is the substance into which the pigment is introduced. In biology, the term “pigment” refers to all coloring matter in a living organism.
Pigments reproduce their colors because they selectively reflect and absorb certain light waves. White color is approximately equal to the mixture from the entire visible part of the light spectrum. When such a wave of light occurs with a pigment, some waves are absorbed by chemical bonds and pigment substituents, while others are reflected. This new spectrum of reflected light creates a certain appearance of color. For example, a dark blue pigment reflects blue light and absorbs other colors.
It has become a little clearer what pigment is, but it must be understood that pigments, in comparison with fluorescent or phosphorescent substances, can only absorb the waves of the light they receive, but not emit new ones. Other color characteristics, such as its concentration or brightness, can be formed from other substances that interact with pigments. Pure dye transmits very few waves of white light, providing a rich color.
History
Naturally occurring pigments such as indigo, ocher, alizarin and iron oxides have been used as dyes from the prehistoric era. Archaeologists have found evidence that primitive people used them for aesthetic purposes, for example, to decorate their bodies. In a cave in Twin Rivers, near Lusaka in Zambia, pigments and tools for their production were found, whose age ranges from 350 to 400 thousand years.
Before the industrial revolution, the variety of pigments available for artistic and other decorative applications was small. Most of the dyes used then were of natural origin. Pigments from non-traditional sources, such as plant matter, insects, and mollusks, were also produced and sold. Some colors were difficult or impossible to make using available shades.
Pigments of rare colors, as a rule, were difficult to acquire, and the technology of their production was kept in secret by the inventors. Such a product was expensive and difficult to manufacture, and objects painted by it were a symbol of power and wealth.
Use of pigments
Different colors have been used since ancient times and have been the main materials in the fine arts throughout history. The main natural pigments used are of mineral or biological origin. The need to obtain less expensive colors, given the lack of certain shades, such as blue, has led to the appearance of synthetically created substances.
Pigments are used to color paint, ink, glass, plastics, textiles, wood, cosmetics, food and other products. Most of them, used in industry and in art, are dry dyes in the form of finely divided powders. Such a composition is added to the "carrier" or "base" - the material is neutral and colorless, which acts as an adhesive. For industrial and artistic applications, immutability and stability are desirable properties.
Pigments, which according to some physical characteristics cannot be permanent, are called volatile. These types of dyes disappear with time or under the influence of ultraviolet light, while others eventually blacken.
How to choose a pigment?
The following are some characteristics of dyes that determine their suitability for certain production processes and applications:
- Toxicity.
- Coloring power.
- Resistance to light.
- Dispersion.
- Heat resistance.
- Opacity and transparency.
- Resistance to aggressive media, including acids and alkalis.
- Reactions between mixed pigments.
The choice of pigment for a particular application is determined by its price, as well as the chemical properties and physical characteristics of the colored substance itself. For example, the pigment used to color the glass must have very high heat resistance to withstand the production process. On the other hand, the glass product must be durable so that it can be used, for example, in the transport industry. The resistance of glass to acid or alkaline materials is not so important.
In art painting, heat resistance is less important, while resistance to light and aggressive environment is fundamental. Another example is the pigment for the tiles that pave the sidewalks. Such a color element must be resistant to fading and destruction under the influence of ultraviolet radiation and precipitation.
Some types and names of pigments
This will help you figure out:
- Carbon pigments: carbon black, black ivory, black vine, black smoke. These are pigments often used in cosmetics. They are an excellent source of a dark shade.
- Cadmium pigments: green cadmium, red cadmium, cadmium yellow, orange. These pigments are highly resistant to acids and high temperatures.
- Iron oxide pigments: red oxide, ocher, red ocher, Venetian red. Essential pigments for paints. Including mineral.
- Chromium pigments: chrome green, chrome yellow. Such pigments are widely used in painting. Very well established in combination with acrylic.
- Cobalt pigments: cobalt azure blue, violet, cobalt yellow. Such substances are very durable and have high opacity. However, the price of this type of pigment is high.
- Copper pigments: Parisian green, Yar-copper, Egyptian blue. These pigments have been used since time immemorial in the painting and art directions. At the moment, they are almost out of use due to their toxicity.
- Biological pigments: alizarin, alizarin-carmine, indigo, cochineal, tyropurpur, phthalocyanine. Universal pigments that are used everywhere: in everyday life, and in the food industry, and in the visual arts.
We can say that pigments are widely used in the modern world.