From the manufacturer:
Winsor & Newton Drawing Inks are formulated from a series of soluble dyes in a superior shellac solution. These inks can be applied with brush, dip pen or airbrush and are widely used by designers, calligraphers and artists as well as illustrators. Fast drying, water resistant & transparent, this allows the overlaying of different colours for attractive optical colour mixtures. All of the drawing inks are water resistant. The white, silver, gold and indian black are also pigmented, meaning they are lightfast.