Lac resin has been used for thousands of years, primarily as a protective coating, dye, and adhesive. It is the only known commercial resin of animal origin, secreted by a tiny scale insect. This amber-colored material serves as the raw material for the refined product known as shellac. The ancient Sanskrit word for lac, lākshā, means “one hundred thousand,” referring to the massive number of insects required for its production. Lac resin maintains global significance in modern industry due to its versatile and durable properties.
Biological Source and Natural Formation
Lac resin begins its life cycle in the tropical and subtropical forests of Asia, most notably in India and Thailand. It is produced by the female of the scale insect species, Kerria lacca, often called the lac bug. These insects are phytophagous, meaning they feed by piercing the bark of certain host trees, such as the Indian jujube, kusum, or palas, and sucking the phloem sap.
Farmers tie an infested twig containing eggs, known as broodlac, to a healthy host tree branch. Once the larvae hatch, they are called “crawlers” and move to a suitable feeding site, settling down to feed. The female insect then begins to secrete the resinous substance around her body, forming a protective, sac-like covering.
The coating protects the sedentary insect and its eggs from predators and desiccation. The insects remain attached to the host tree throughout their life cycle, which typically spans about six months. When the lac-encrusted branches are harvested, the raw material is referred to as “sticklac” because it consists of the resin, insect remains, and pieces of the host twig.
Refining Raw Lac into Shellac
Sticklac is converted into shellac through a series of purification steps. The initial stage involves crushing the harvested branches to separate the resin from the wood, followed by washing the material with water. This washing removes impurities like insect parts, twigs, and a naturally occurring water-soluble dye called lac dye.
The resulting granular material, referred to as “seedlac,” is partially purified and dried, retaining a small percentage of impurities (around three to five percent). The final purification involves melting the seedlac, often using heat or a solvent process, followed by filtration.
In the traditional hot-filtering method, the melted lac is squeezed through a cloth filter, and the filtered molten mass is either stretched into thin sheets or allowed to solidify into discs. When stretched and broken, these sheets form the familiar shellac flakes, which are the primary commercial form of the resin. Alternatively, the solvent process dissolves the seedlac in alcohol and filters it to produce high-purity, sometimes dewaxed, shellac.
Diverse Uses Across Industries
Refined shellac is valued for its non-toxicity, rapid drying time, and ability to form a moisture barrier. One traditional application is in wood finishing, where it is dissolved in alcohol to create a quick-drying varnish known as French polish. This finish serves as a durable sanding sealer, primer, and high-gloss coating that blocks stains and odors.
The food industry utilizes shellac as a glazing agent, identified by the European food additive number E904. It is applied to confectionery items like candies, chocolate-covered nuts, and baked goods to provide a glossy finish and prevent them from sticking together. Shellac is also used as a protective wax coating on fruits, such as citrus and apples, to prolong shelf life by preventing moisture loss.
In the pharmaceutical and cosmetic sectors, shellac’s barrier properties are harnessed for specialized applications. It is used to coat tablets and capsules to create an enteric coating, which prevents the medication from dissolving prematurely in the acidic environment of the stomach. The coating can also be engineered to facilitate a time-release action. Due to its film-forming and binding capabilities, shellac is also incorporated into cosmetic products like mascara and nail polish.