Shellac comes in two forms: in a can, mixed and ready to go, or as hard flakes. Canned shellac is convenient to use—just pop open the lid and dip in your brush—but it has a limited shelf life; an unopened can is good for only about three years. Flakes will last almost indefinitely when stored where it's cool, dry, and dark. When you need to give something a shellacking, just mix the flakes in denatured alcohol the day before.
Here's the recipe.
Measure. The ratio of shellac to alcohol—its "cut"—is measured in pounds. A pound of shellac in a gallon of alcohol is called a one-pound cut. The heavier the cut, the thicker each coat of shellac will be and the fewer square feet it will cover. Most canned shellac is a
2-pound cut. Measure out the amount of alcohol you intend to use—1 pint covers about 40 to 50 square feet—then weigh the flakes on a kitchen scale. For a
2-pound cut in a pint of alcohol, use 4 ounces of flakes.
Mix. Pour the alcohol into a glass container with a lid. Stir in the flakes, close the lid, and give the jar a shake every 10 minutes or so for an hour, then let it sit overnight for the flakes to dissolve. The shellac will be ready to use the next day and should last for 6 to 12 months.
Filter. Before you start shellacking, stir the mix, then filter it into a separate container through a cotton T-shirt to remove any undissolved bits.