Shellac is just that... a varnish type compound... derived naturally as mentioned in the post above. It's available at about any hardware store, though most furniture refinishers recommend not buying pre-mixed from a hardware store, since you don't know how old it is... it's best used when fresh... It doesn't dry properly if not fairly fresh (less than a few months old). That's why furniture refinishers generally mix their own. If you're considering shellacing a sculpt (as in the ADI book), I'd just recommend using 3 or 4 coats of Crystal Clear... If you don't know what you're doing with shellac, you're probably going to end up ruining your sculpt if it ends up not drying properly.