Shellac cut calculator

What a pound cut means

A "pound cut" is the weight of dry shellac flake dissolved in one US gallon of alcohol. A 2 lb cut is two pounds of flakes in a gallon of alcohol, which is 8 ounces in a quart or 2 ounces in a cup. The gallon is the alcohol, not the finished mix: flakes add volume of their own, so a gallon of alcohol with three pounds of flakes in it makes well over a gallon of shellac.

Zinsser premixes its Bulls Eye shellac at a 3 lb cut. Its data sheet says it may be used straight from the can, but recommends thinning it first for the best results. More on the finish itself: shellac.

Why thinning is not a simple ratio

If you treat a 3 lb cut as "3 lb per gallon of liquid" and dilute by volume, you add too little alcohol. The flakes take up about a tenth of a gallon per pound (shellac is a little heavier than water), so a quart of 3 lb cut holds only about 0.19 gallon of alcohol. The calculator works out how much alcohol and how many pounds of flake are really in your shellac, then adds the alcohol the new cut needs. It assumes the two volumes simply add, which is close enough for finishing.

Zinsser prints its own whole-part chart for its cans: 2 parts alcohol to 5 parts shellac for a 2 lb cut, 3 to 2 for a 1 lb cut, and 1 to 1 to take a 2 lb cut to 1 lb. The calculator's answers land within 10 % of each row; the chart rounds to whole parts.

How to read the answer

Weigh the flakes rather than measuring them by the cup: flakes pack differently, so a cup has no fixed weight. The thinning answer carries a source tag for the flake density it rests on, and a line showing how little the answer moves across the range the sources give. Open "Why these numbers?" for each step and its sources.