Shellac is a natural resin used for centuries across various industries, from woodworking to confectionary. This versatile substance originates from an insect, specifically as a natural polymer secretion harvested from host trees. The production of this unique finish involves a multi-stage process that transforms the raw material into a refined product used globally.
The Source of Shellac
Shellac originates from the tiny insect species Kerria lacca, commonly known as the lac bug, native to the forests of India and Thailand. This scale insect, related to mealybugs and aphids, produces the resin as a protective covering while feeding on the sap of host trees. The female lac insect primarily secretes this resinous material during its six-month life cycle.
The insects colonize tree branches, piercing the bark to feed on the phloem and secreting the resin through pores. This secretion quickly hardens upon contact with air, forming a continuous, amber-colored crust over the colony and the twig. The raw material scraped from the branches is called “sticklac,” an impure mixture containing the resin, tree bark fragments, and insect remains. Estimates suggest that between 17,000 and 90,000 lac insects are needed to create just one pound of shellac.
From Resin to Polish
The journey from raw sticklac to refined shellac involves several purification steps to remove biological and physical impurities. Harvested sticklac is first crushed to detach the resin from the bark. The crushed material is then washed, removing the water-soluble lac dye and the majority of insect bodies and debris.
This initial washed and dried product is known as “seedlac,” which still contains impurities like wax and insoluble matter. Seedlac is then further refined using one of two primary methods: hot-filtering or solvent extraction. In the traditional hot-filtering method, the seedlac is heated until it melts, allowing the molten resin to be strained through a cloth to filter out remaining impurities.
Alternatively, the solvent method involves dissolving seedlac in an appropriate solvent, typically industrial alcohol, and filtering the solution to remove insoluble matter. The resulting resin is dried and stretched into thin layers, cooled, and broken into flakes, the form in which shellac is usually sold. The natural color is orange, but it can be bleached with sodium hypochlorite to create white shellac, often dewaxed for specific applications.
Common Uses of Shellac
Shellac is valued for its unique properties, including its ability to form a hard, durable, non-toxic film highly resistant to oils. Its application in woodworking is widespread, used as a high-gloss finish, a primer, and a sanding sealer. The finish is prized for the traditional “French polish” technique, which imparts a deep, warm glow to furniture and musical instruments.
The substance is widely utilized in the food and pharmaceutical industries because it is considered safe for human consumption once dry. As a food additive, it is often referred to as confectioner’s glaze, food glaze, or the European code E904. This coating is applied to candies and chocolates to provide a glossy sheen and prevent them from melting or sticking together.
In the pharmaceutical world, shellac coats medicinal tablets and capsules. Its acidic properties allow it to resist breakdown in the stomach, creating enteric coatings that ensure medication is released later in the digestive tract. Shellac also acts as a sealant on citrus fruit to prolong shelf life and is found in cosmetics, such as mascara and hair spray.