Shellac Guide

Shellac is scraped from the bark of the trees where the female lac bug, Laccifer (Tachardia) lacca Kerr, Order Hemiptera, Family Coccidae[2] deposits it to provide a sticky hold on the trunk. This bug or insect is in the same family as the insect from which cochineal is obtained. The insects suck the sap of the tree and excrete "stick-lac" almost constantly. The least coloured shellac is produced when the insects are parasitic upon the kursum tree, (Schleichera trijuga). The raw shellac, which contains bark shavings and lac bug parts, is placed in canvas tubes (much like long socks) and heated over a fire. This causes the shellac to liquefy, and it seeps out of the canvas leaving the bark and bug parts behind. The thick sticky shellac is then dried into a flat sheet and broken up into flakes when dried, or dried into "buttons" (pucks/cakes), and then bagged and sold. The end-user then mixes it with denatured alcohol on-site a few days prior to use in order to dissolve the flakes and make liquid shellac.

Liquid shellac has a limited shelf life (about 1 year), hence it is also sold in dry form for dissolution prior to use. Liquid shellac sold in hardware stores is clearly marked with the production (mixing) date, so that the consumer can know whether the shellac inside is still good. Alternatively, old shellac may be tested to see if it is still usable: a few drops on glass should quickly dry to a hard surface. Shellac that remains tacky for a long time is no longer usable. Storage life depends on peak temperature.

The thickness (strength) of shellac is measured by the unit "pound cut", referring to the amount (in pounds) of shellac flakes dissolved in a gallon of denatured alcohol. For example: a 1-lb. cut (said as "one pound cut") of shellac is the strength obtained by dissolving one pound of shellac flakes in a gallon of alcohol. A 5-lb. cut is the strength of five pounds of shellac flakes dissolved in a gallon of alcohol. Most pre-mixed commercial preparations come at a 3-lb. cut. Multiple thin layers of shellac produce a significantly better end result than a few thick layers—thick layers of shellac do not adhere to the substrate or to each other well, and thus can be peeled off with relative ease; in addition, thick shellac will fill in (and thus ruin) carved designs in wood and other substrates.

Shellac naturally dries to a high-gloss sheen. For applications where a flatter (less shiny) sheen is desired, products containing amorphous silica,[3] such as "Shellac Flat," may be added to the dissolved shellac.

Shellac naturally contains a small amount of wax (3%-5% by volume), which comes from the lac bug. In some preparations, this wax is removed (the resulting product being called "dewaxed shellac"). This is done for applications where the shellac will be coated with something else (such as paint or varnish), so that the topcoat will be able to stick. Waxy (non-dewaxed) shellac appears milky in liquid form, but dries clear....