Lac (Laccifer lacca or Kerria lacca)
Lac extract yields crimson and burgundies to deep purples with the addition of iron.
Lac is probably one of the most ancient dyes, as its use extends to the beginning of recorded history. The dye is taken from the insect Kerria Lacca. It is cultivated and found wild on fig and acacia trees in India, Southeast Asia and China. The principal coloring component in this dye is Laccaic Acid. I have read that it has very good wash and lightfastness on protein fibers, silk and cellulose fibers, but another source said that it had reduced light and wash fastness on cellulose fibers.
The female lac insects invade the host tree and secrete a resin that contains the dye. The resin covers the colony, and when harvested in chunks, it is known as stick lac. The dye must be extracted from the resin before it can be used to dye fibers. If using sticklac, extract the dye from the resin by boiling it in a strong vinegar/water solution. Continue to cook it until the resin is almost clear. Strain and use. The resin is used to make shellac.
Like cochineal, lac is pH sensitive. The presence of acid will shift the color towards red. Do not use acids when dyeing mordanted cellulose fibers. One source said that citric acid should be used when dyeing with Lac, and I think that was mentioned because the dye sources in lac are combined with sugars and proteins, and so the addition of acids to the dye bath may help release the dyes from the sugars. But again, don’t use citric acid when dyeing mordanted cellulose.
5-12% weight of fiber is all that is needed for a medium shade.
Use alum mordant at 15% WOF (weight of fiber) to mordant protein fibers such as wool and silk. For cellulose fibers mordant with tannin at 8% WOF and then alum at 15%, or alum acetate at 8%. If you use cream of tartar (tartaric acid) at 6% WOF and add it to the alum mordanting bath or the dyebath, the color achieved will be more red.