What kind of substance is a pigment, its description and properties in the composition of dyes
People often wonder what pigments are. This term refers to substances of a certain color that selectively absorb the wavelength of light. Although many materials have these characteristics, pigments for practical use are stable under normal temperature conditions and have a high degree of color fastness.
The concept and properties of pigments
From Latin, the word "pigment" is translated as "paint". This substance in the composition of dyes has the finest grinding. It differs from conventional paints in that it does not dissolve in water. In addition, the substance does not mix with compounds that form a film on the surface of certain types of materials.
Pigments have their own characteristics and properties. These include in particular the following:
- Physical parameters. All substances in this category include many small crystals. They have a high density and hardness. Each pigment has its own shade. In this case, the shapes and sizes of the particles are different. With this in mind, there are fine and coarse compositions. Pigments are characterized by low solubility indices.
- Chemical parameters.All pigments are characterized by high resistance to water and various chemical elements. They hardly dissolve in such substances.
- Technological parameters. Pigments are characterized by different color intensities. Not all substances can react with other types of reagents in the system. The shades of pigmented paints depend on this.
- Physico-chemical parameters. Pigments have different levels of wettability. They differ in different levels of adsorption.
Classification
Today, many types of pigments are known, which differ in their characteristics and characteristics.
Natural iron oxide
Such pigments are characterized by resistance to light and atmospheric factors. They also differ in their opacity for ultraviolet radiation. Disadvantages include low color saturation and relatively low dispersion.
The main iron oxide dyes include:
- Ocher is a natural crystalline iron hydrate with a mixture of clay. Ocher can have different shades of yellow. The color is influenced by the content of hydrated iron oxide.
- Siena - they differ from ordinary ocher in an increased level of iron and hydrated water. At the same time, there is practically no clay in the composition. Instead, silicic acid is present. Many varieties also contain manganese oxide.
- Shade is a product of the weathering of iron ore, which contains manganese. It is carried away by water and accumulates in the cracks of the strata in the form of a dense earthy mass. Shade is available in natural and burnt varieties. The composition of the natural variety is close to ocher, but it contains manganese.The burnt shade varies from light brown to darker.
artificial mineral
This category includes pigments, which are oxides of heavy metals, salts of various origins and other substances.
This includes iron oxide substances, the color of which is due to the presence of one of the iron oxides.
The composition of substances may contain iron oxide, hydrated iron oxide or iron oxide-oxide. Components affect color:
- yellow pigments are associated with iron oxide hydrates;
- black - represents iron oxide;
- red - contains iron oxide;
- brown - consisting of hydrated iron oxide.
white mineral
This category of pigment includes the following:
- Titanium white is a relatively new material made from titanium dioxide. The increased refractive index of the substance, in combination with the whiteness, provides a high level of opacity. By this parameter, titanium white is superior to other white pigments.
- Zinc white - in its pure form it is distinguished by a bluish color and absolute whiteness. The advantages of the material include low toxicity, complete lightfastness, suitability for any type of paint. In addition, the substance can create strong mixtures with any paint. At the same time, zinc white also has disadvantages. These include low opacity, insufficient drying when applied to oil, and the risk of cracking.
Cadmium paints
These pigments are formed on the basis of cadmium sulphate and zinc sulphate. Their color is distinguished by great purity and intensity. These dyes are yellow and brown. In this case, it is worth considering the following characteristics of these substances:
- blacken when mixed with lead-based dyes;
- color change in paint formulations based on iron oxides;
- in compositions with blue pigments, they make it possible to obtain a range of beautiful shades of green;
- do not change the original color when drying;
- are distinguished by high coverage capacity;
- light colors are best mixed with nut butter.
The reddish types of cadmium paints are based on cadmium sulfide and selenide. Their shade depends on the amount of the last ingredient. The higher its content, the more saturated the shade of the dye.
The distinguishing characteristics of these substances are as follows:
- do not change shade after drying - such paints retain a rich, bright shade;
- are distinguished by high covering power;
- tarnish when added with pinene.
The substances are characterized by high light stability. They do not change under the influence of sulfur gases and hydrogen sulphide.
Cobalt paints
In terms of chemical composition, cobalt pigments are a mixture of cobalt oxide with various metal oxides. Thus, the following types of cobalt are distinguished:
- Light with a cold tint - considered a solid solution of spinels.
- Dark is a composition based on zinc oxide, cobalt oxide and alumina.
- Blue is a spinel-like cobalt aluminate that includes zincate and phosphate impurities.
- Dark purple - considered dehydrated cobalt phosphate.
- Light purple - consists of a double ammonium-cobalt salt of orthophosphoric acid.
The distinctive characteristics of cobalt paints are:
- relate to glazing substances;
- dry quickly;
- they differ in drying characteristics - in combination with other paints, drying is accelerated;
- have medium intensity.
Chromium
These paints are made on the basis of a chromium oxide pigment. It has a soft green tint. Typical properties of chromium oxide are:
- has a high hiding power;
- immediately shrinks when spreading on the ground;
- should be mixed with varnish or bleached oil for fine application;
- allows connection with all dyes.
The paint is characterized by a high degree of lightfastness.Under the influence of hydrogen sulfide and sulfur gases, the substance does not change its original color.
Another variety of such paints is considered emerald green. The pigment is a hydrated chromium oxide. The dye has a dark green tint of a cold tone. Mixed with lime, it is possible to obtain a blue-green tint.
Emerald green is considered a low intensity paint. In addition, it has a deep and pure color. Characteristics of the substance include:
- included in the category of icing substances;
- spreads easily on the canvas - no dilution is required to apply the composition in a thin layer;
- if thinning is necessary, it is recommended to use Pinene or Thinner No. 2.
Organic
Organic matter is obtained from plant matter or insects. Unlike mineral pigments, these substances are easily soluble in water, alcohol and oil. At the same time, organic substances are not characterized by such high strength as synthetic substances. These pigments do not form a paint layer, but penetrate the surface structure. Therefore, they are often used to dye fabrics.
Kraplak is considered a popular representative of this category.It is made from madder or speck roots. Another common herbal composition is indigo. It is obtained from pastel. It is allowed to use marine molluscs as raw materials for the manufacture of paints. A light brown pigment is made from them. By calcining from organic matter, it is possible to create black coloring components.
Today there are many varieties of pigments that differ in color and characteristics. When using a specific substance, it is imperative to study its properties.