Shellac/Waterborne Caveat
For all who, like I, use shellac as a barrier/binding coat under waterborne finishes, please note that there have been a number of problems with cracking finishes with this combination. It was first noticed by several of the high-end waterborne manufacturers like Target Coatings, and involved Zinsser's SealCoat shellac, a commercial premixed dewaxed bleached shellac. Further anecdotal evidence (including my own) indicates that when using shellac under a waterborne finish, you need to have freshly mixed product and restrict your use of the shellac to no more than 2 thin coats that are allowed to dry thoroughly for at least 24-36 hours before topcoating with waterbornes. Since I use dewaxed shellac in the darker grades as a toner, I've had to go to the addition of dyes to the shellac mix to get the same result.
Also, when mixing shellac from flakes, you will be better served to use a high-ethanol content alcohol (some are more than 50% methanol), and filter your mix twice through coffee filter material to reduce wax content to a minimum.