Organic dyes

Dyes of plant and animal origin
These dyes were known and used in ancient times, nowadays they are not likely to be used anymore. For the most part, organic dyes are perishable, with the exception of kraplak and Indian yellow. They lose color when exposed to light or combined with lead and copper dyes.
The binder with which they are grated is also of great importance. For example, some of the dyes grated with egg white acquire extraordinary durability.
Properties:

1.Harmless to health.
2.Laser-like.
3.More or less sensitive to light.
4.They dry slowly in oil.

Indian yellow

Golden yellow shade. Quite permanent in light. More durable in oil than in watercolor (has the ability to partially dissolve in water).
Outstandingly laser-like. Oil takes 100%. Dries slowly.
Recognition:
In hot hydrochloric acid, it gives a solution that precipitates a white precipitate when cooled.

Kraplak

Known in ancient times, still used today. It is obtained from the root of marzanna.
The dried root is ground into a powder of yellow-red color. The plant is native to Cyprus. Its root contains a number of coloring compounds, the most important of which are alizarin and purpurin.
In addition to alizarin and purpurine, which give the color red, the marzanna root has such components as rubiacin (yellow), chlorogen (green) and erythrosine (brown), which are used to produce stand-alone dyes of these hues, as well as to impart different shades to kraplak.
In this way, yellow and brown kraplak are obtained.
The most durable dyeing ingredient is alizarin. Nowadays, the production of dyes from marzanna roots is carried out in a very complicated way by leaching the coloring ingredients and depositing sodium carbonate.
Alizarin with clay and lead oxide gives seal wax red. With iron oxide - purple, and with chromates - brown.
Burnt kraplaks are also encountered commercially. They do not contain water in their composition and thus are less prone to cracking.
They have a purple tint.

Red kraplaks

They are the only dyes from the group of organic dyes used in all techniques, not excluding fresco and stereochrome.
They dry slowly in oil and need up to 70% of it.
Kraplaks grated in butter when stored for long periods of time will gelatinize (the action of the free fatty acids in the oil on the clay in the kraplak).
Red kraplaks are the most durable. Light - sensitive to light.
Currently, alizarin is produced artificially from gas tar. Synthetic alizarin is not inferior in quality to natural alizarin.
Craplak does not combine with greens or green primers.
Recognition:
Yellow craplacs color red in hydrochloric and sulfuric acid solutions.
Red craplak in concentrated hydrochloric and sulfuric acid yields a yellow color.

Carmine

Carmine was discovered in the 16th century.
In the 16th century, it was an essential pigment in oil and watercolor techniques.
In oil technique, it lost its popularity by drying very slowly. It is a dye that is eminently impermanent to light.
The raw material for the production of carmine is aphids parasitizing the cactus (America, Mexico). From these aphids, the so-called carminic acid is obtained.
Recognition:
It dissolves in ammonia.

Gumiguta

Laser-like, bright yellow dye.
It is a combination of dyed resin and vegetable glue. The so-called "gumiguta seal wax" consists of a coloring substance - gummi gutta and clay.
The durability of gumigut depends on the species of dye and the binder.
In watercolor and with pure oil it discolors. With resins and wax it is durable. Its durability is increased in combinations with baryta yellow and cadmium.
Gumiguta was used by medieval painters.
Recognition:
In dilute hydrochloric acid it does not change.
When alkali is added, it tints red.

Indigo

It is obtained from the plant indigafera disprema, a coloring compound - indigotion (blue).
Indigotion was obtained synthetically in the 19th century.
Natural indigo was known in Egypt. Later, widely used in the Renaissance, destroyed many works of famous painters (Veronese).
More durable in watercolor than in oil, but also discolors.
In oil it greens, blackens and hides poorly. In a thin layer it gives a shade of blue, light, in thicker layers - dark blue, almost black.
Artificial indigo is purer and more pleasant in tone than natural indigo, as the latter has a certain amount of by-products, weakening its durability and contaminating the color.

Sepia

A brown, lasing pigment, the most popular in watercolor.
Not resistant to light, but not to the same extent as other brown dyes of organic origin.