The best material for a shim is a thin piece of maple veneer. Most bolt-on necks are made of maple, so it makes sense to make a shim from the same material. The wood can be easily shaped to fit the neck pocket and angled to the proper degree. I typically start with a piece of maple about .060 thick.
Lignin is a class of complex organic polymers that form important structural materials in the support tissues of vascular plants and some algae.[1] Lignins are particularly important in the formation of cell walls, especially in wood and bark, because they lend rigidity and do not rot easily.
Indican (noun) a glucoside obtained from woad (indigo plant) and other plants, as a yellow or light brown sirup. It has a nauseous bitter taste, a decomposes or drying. By the action of acids, ferments, etc., it breaks down into sugar and indigo. It is the source of natural indigo. Indican (noun)