Don't buy the Zinsser shellac. Buy their Sealcoat product which is actually a high grade dewaxed amber/blonde shellac. It lasts a long time in the can, has improved moisture resistance, and is less likely to get sticky over time as regular shellacs have a tendency to do. I frequently use shellac in my woodworking and Sealcoat is a superior product. I don't bother making up flakes into solution anymore.
http://www.rustoleum.com/en/product-...sanding-sealer