Gallnut or Oak Gall is used to mordant cellulose fibers and fabrics before the alum mordant is used. Alum does not combine as readily with cellulose fibers as it does with protein fibers.
Tannin has a great affinity with cellulose fiber and once mordanted with tannin, alum combines well with the tannin-fiber complex.
Gallnuts from the oak tree are the earliest and richest source for natural tannin. They are produced by insects who deposit their eggs in small punctures they make on young branches. As a protection, the tree excretes a tannin rich substance that hardens and forms into a gallnut. These are collected and ground for use as a tannin mordant.
Gallnuts are used in the leather tanning industry, and for in some medicines.
Use at 6-8% WOF.