Ultramarine dyes

Ultramarine blue - sodium aluminum silicate

Color: light blue to purple.
Properties:

1.Lightfast.
2.Non-poisonous.
3.Fairly resistant to alkali.
4.Not resistant to acids (especially weak acids).
5.Subject to the so-called "ultramarine disease".

"Disease" of ultramarine consists in changes occurring in the crystal structure and is a physical phenomenon. Ultramarine turns gray, loses its color due to the effects of moisture in the air, CO2 and in oil technique - fatty acids (sensitivity to weak acids). Treatment consists of applying compresses of cape balsam and spirit (Petenkoffer method) or spirit vapor.

Natural ultramarine

The mineral lapis lazuli - a semi-precious stone, as a mineral difficult to work, coarse-grained, expensive.
Used since the 15th century.

Ultramarine green

Used primarily in wall technique. Better grades also in painting.
Has all the properties of ultramarine.

Ultramarine violet

Formed by the action of chlorine and steam or hydrochloric acid on ultramarine blue.
The color is not very pretty. In terms of durability, it is inferior to cobalt violet.
Recognition:
Pure ultramarine decomposes in all weak acids to form a colorless gelatinous liquid.
Ultramarine is often colored with Paris azure, tartar, indigo and starch.