Dye varnish
Dye varnish or Lac Dye (more rarely also Lac Lac ) is a natural dye ( CI Natural Red 25) that is used as a pigment in a laked state . It is obtained from the rubber lacquer (stick lacquer), the resinous secretion of lacquer scale insects .
history
Manufacturing
There are two types of dye varnish: To make Lac Dye, the stick varnish of the lacquer scale insects is crushed in stone mills and the powder is agitated in warm water for hours to dissolve the dye. The water is then evaporated in kettles over the fire or dried in the sun in shallow vessels. The dye comes in the form of flat cakes.
Alternatively, the dye of the ground stick varnish is dissolved by boiling with a dilute soda or potash solution, filtered and the colored varnish is precipitated from the filtrate with alum solution . The precipitate is dried and sold in small squares. This shape is known as Lac Lac also Lac Lake .
The residue in both methods is the so-called grain lacquer , which is processed into shellac .
properties
Dye varnish is a yellowish red powder that is soluble in various solvents such as ethanol , methanol , acetone and acetic acid. The dye is sparingly soluble in water. It is very heat resistant, melts at 180 ° C and decomposes at 230 ° C.
The dye is composed of 50% laccainic acids , 25% resin, 22% solid components: aluminum, iron, calcium carbonate and sand. The coloring component of the dye varnish are the laccainic acids, anthraquinone dyes , which are similar to the carminic acid of the real carmine or the kermic acid from the kermes .
use
The dye is very similar to that of the cochineal and that of the Kermes scale insects. Both preparations were mainly used to dye scarlet and crimson on cotton and silk. Red lacquer shades are softer and warmer than carmine. It was also used to dye leather and carpet wool. As a replacement dye for henna , Lac Dye was also used to dye hair and fingernails; it is also suitable for oil painting .
A solution of Lac Dye in a mixture of hydrochloric acid and tin (II) chloride forms the Lac Spirit . Another preparation is Ofenheimer Rot , powdered Lac Dye is mixed with 4.5 times the amount of 80% ethanol, heated and pressed. The resin dissolves and the dye remains.
Today, dye varnish is mainly used in textile dyeing and for restoration purposes.
literature
- Sabine Struckmeier: Textile dyeing from the late Middle Ages to the early modern period. Waxmann, 2011, ISBN 978-3-8309-2527-9 , p. 106 ff.
- Otto Lueger : Lexicon of the entire technology . Volume 3, Stuttgart, Leipzig 1906, p. 641.
Web links
- Lac Dye on materialarchiv.ch, accessed on January 4, 2017.
Individual evidence
- ^ Heinz A. Hoppe: Drug Science. Volume 2, 8th edition, De Gruyter, 1977, ISBN 978-3-11-084414-6 , p. 276.
- ↑ Julius Wiesner : The raw materials of the plant kingdom. Volume 1, 4th edition, Engelmann, 1927, p. 384.
- ^ Lac Dye. Kremer Pigments, accessed December 10, 2018 .
- ^ Meyers Konversations-Lexikon. Volume 10, 4th edition, Verlag des Bibliographisches Institut, Leipzig and Vienna 1888, p. 387.