Shellac is a natural resin refined from Lac, the resinous secretion of the tiny scale insect Kerria lacca, which is parasitic on certain host trees in India.
Dewaxed Shellac is refined from Seedlac using the Solvent Extraction Process. It is extracted by dissolving the Seedlac in a solvent, usually ethanol. The solution is then filtered through a fine cloth which removes any insoluble matter and most of the naturally occurring wax contained in the Lac.
The solution is sometimes further filtered using activated carbon to lighten the colour of the Shellac. The alcohol is recovered by evaporation, while the remaining viscous Shellac is stretched into a thin film using a roller before being broken into flakes once cool.
Dewaxed Shellac is sold in flake form and typically contains ≤0.2% wax. It is soluble in alcohol and aqueous alkaline solutions and is available in a variety of grades that are categorised by colour, usually by reference to the Gardner or Lovibond scales.
The Gardner colour scale measures the shade of yellow of transparent liquids. Shellac colour grades are determined after dissolving a sample in an 20% ethanol solution and comparing it with a known standard. The Gardner colour range extends from 1 (almost transparent yellow) to 40 (dark brown).
