Indigo Quality No. 1 [100 g bag] (3.5 oz.)
Item No: 415:110100
Colour Index: Not Listed
ASTM Lightfastness: Not tested
Hardness: 2 Density: 2.6 Chemical Formula: C16H10 N2O2
Origin and History
Indigo is the name given to blue pigments prepared from certain plants, the active ingredient of which is an indol derivative found in the leaves, is fermented from a sugar. There are more than ten plants in the world, such as Tree Indigo (Indiagofera tinctoria) from India or Woad (Isatis tinctoria) from Europe, which contain the indigo pigment (Indigotin). The plant Indiagofera tinctoria thrives in the tropical climate of India and is the source of our pigment.
Ancient Greeks and Romans probably used indigo as a painting pigment. In the 13th century, Marco Polo was the first to report on the preparation of indigo in India.
Preparation of Dye
To prepare the dye, freshly cut plants are soaked until soft, packed into vats and left to ferment. It is then pressed into cakes for use as a watercolor or dried and ground into a fine powder for use in making lake pigments. A healthy vat will have a collection of rich purple-blue bubbles and film across the surface. These oxidized bubbles are known as aibana or indigo blossoms. The aibana are gently removed from the surface of the vat and allowed to dry. This is one of the purest forms of indigo and is used in making a lake pigment of indigo.
Some of the various chemical tests by which indigo may be identified are: sublimation test, nitric acid test, hydrosulfite test, solubility tests, and thin-layer chromatography. Indigo is characterized as having a good lightfastness (light resistance), good to moderate alcohol resistance, and low oil resistance. Indigo's chemical properties make it difficult to dissolve in hot ethanol, amyl alcohol, acetone, ethyl acetate, and pinene, but readily soluble in boiling aniline, nitrobenzene, naphthalene, phenol and phthalic anhydride. It is heat resistant to 150° C and is resistant to air. The precipitation is insoluble in water. Alkalis dissolve it and form the sodium salt indigo white, which oxidizes into many shades of blue.
Indigo does not hold up in an oil base. It has fair tinting strength and may fade rapidly when exposed to strong sunlight. Worked in tempera or beneath varnish it can be very stable. It is also stable when exposed to hydrogen sulfide.
Preparation of Lake Pigment
A lake pigment is a natural organic pigment prepared when a dye has been precipitated on a powdered, colorless, inorganic substrate. The term derives from the Latin word lacca, used in the Middle Ages to denote both lake pigments and the Lac dye. Because of its transparency, aluminum hydroxide is the most commonly used substrate or carrier. Barites, such as barium sulfate, provide an opaque lake pigment. Other compounds used as carriers are: chalk, clay, gypsum, tin oxide, zinc oxide, white earth, and green earth. Often a mordant, such as tannic acid, lactic acid, or sodium phosphate, is used to fix the dye to the substrate.
Indigo is usually 'struck' or precipitated onto a base or substrate (aluminum hydrate, calcium sulfate, barium sulfate) to form a lake pigment.
100 gram bag
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