Shellac is generally made from two ingredients, raw seed lac and ethyl alcohol. In fact, most companies want to purify shellac as completely as possible—impurities from the bug, the cocoon etc. are removed, as are natural waxes. Shellac is generally shipped in dry or flaked form and is re-moisturized with an alcohol solvent, generally denatured alcohol. Some companies add ingredients to lengthen the shelf life of their product but will not reveal these proprietary additives. Shellac that is bleached (or made into clear shellac) are dissolved in sodium carbonate and centrifuge to remove insolubles and then bleached with sodium hypochlorite.
The Manufacturing Process:
The role of the lac bug:
1 Shellac is produced by a tiny red insect. Swarms of the insects feed on certain Shellac trees, primarily in India and Thailand, known informally as lac trees. The lac bugs' life cycle is only six months, in which time they eat, propagate, and secrete the resin they've taken in from the tree to produce shellac.
In certain seasons of the year, these insects swarm in huge numbers on the trees, settle on branches, and project protrusions into the tree to penetrate the bark. They suck up the sap and absorb it until they feed themselves to death (called the feast of death amongst the indigenous peoples). At this same time, propagation continues, with each female lac bug laying about 1,000 eggs before dying.
The sap is chemically altered in the lac bug's body and is then exuded onto the tree branch. On contact with the air, the excretion forms a hard shell-like covering over the entire swarm. This covering forms a crust over the twig and insects. As the female lac bug is exuding the ingested sap she is preparing to die and is providing a fluid in which her eggs will mature under protection. The males' role is to fertilize the female, and it is after fertilization that the females' lac output is vastly increased. The adult males and females become inactive, and the young start to break through the crust and swarm out.
Refining the crusty resin:
2. Workers cut millions of encrusted branches, called sticklac, for transportation to refineries of some sort (either handrefined or mechanically refined). Some workers use mallets and break off the crusty coating much as ice is broken from branches in the winter (it is referred to as grainlac).
3. At refining centers, sticklac is scraped to remove the secretions from the twigs. Sticklac and grainlac is ground with rotating millstones. The resulting ground material is quite impure, containing resin, insect remains, twigs, leaves, etc. The mixture is forced through a screen, removing the largest of the impurities.
4. The sifted resin mixture is put into large jars and stomped by a worker to crush granules and force the red dye from the lac seeds and the insect remains will be freed from the resin. Dye water, scum, and other impurities are then washed away in several rinsings. The mixture is spread out on a concrete floor to dry and called seedlac because it resembles seed. Seedlac is the raw material from which both orange shellac and bleached or clear shellac are produced. Shellac may be made from seedlac by hand or by modern mechanical equipment.shellac is refined with the help of machinery, using a heat-or solvent-based process.
5. Seedlac is melted onto steam-heated grids. The molten lac is forced by hydraulic pressure through a sieve or screen, either of cloth or fine mesh. The filtered shellac is collected and transferred to a steam-heated kettle, which then drops the molten liquid onto rollers. The liquid is squeezed through the rollers and forced into large, thin sheets of shellac. When dry, this shellac sheet is broken into flakes and transported to another area in which the flakes are combined with denatured alcohol to produce the consumer's shellac
6. In this process, the seedlac and solvent, usually ethyl alcohol, are mixed in a dissolving tank, refluxed for about an hour and then filtered to remove impurities. The filtered resin is sent through evaporators that remove the alcohol solvent, rendering it a viscous liquid. This liquid is then dropped onto rollers, which force it into sheets. The sheets are then are dried and flaked apart.
Despite the removal of much of the red dye from the lac seeds in the refining process, shellac remains an orangish solution after processing is complete. Some consumers prefer a clear shellac finish, so manufacturers have developed a way to bleach the color from the shellac.
7. Bleaching begins with dissolving seedlac, which is alkali-soluble, in an aqueous solution of sodium carbonate. The solution is then passed through a fine screen to remove insoluble lac, dirt, twigs, etc. The resin is then bleached with a dilute solution of sodium hypochlorite to the desired color. The shellac is then precipitated from the solution by the addition of dilute sulfuric acid, filtered, and washed with water. It is dried in vacuum driers and ground into a white powder ready for shipment to a plant that will add liquid to the flakes.
Mixing shellac for the consumer:
8. Large shellac manufacturers are shipped the dry shellac flakes. They then remoisturize the flakes by adding denatured ethyl alcohol. Shellac is offered to the consumer in flake form or suspended in denatured alcohol. It is the latter than is most popular with the consumer. Manufacturers of shellac refer to the concentration of shellac flakes to denatured alcohol in terms of pounds of cuts—the number of pounds of shellac flakes dissolved into a single gallon of denatured alcohol. Thus, a one pound cut of shellac contains one pound of shellac flakes dissolved in a gallon of alcohol—very dilute shellac. The manufacturers' standard cut offered to the consumer pre-mixed is termed a three pound cut. Some consumers then dilute it further with denatured alcohol if they so desire
The most popular shade of shellac sold premixed is the orange shellac although clear or white shellac is also offered pre-mixed to the consumer. Manufacturers always stamp the date of mixing of the shellac into the can. Each manufacturer has a recommended shelf life for the product and the consumer should heed that the product is not used after the period suggested by the manufacturer. If used after the time span recommended, the shellac may never dry completely.
For woodworkers who prefer the deep rich colors of garnet shellac or buttonlac, the dried flakes of these shellacs may be purchased from the manufacturer and mixed with denatured alcohol by the consumer.
The denatured ethyl alcohol used in the process of manufacturing shellac is a strictly regulated byproduct and is known as a volatile organic substance (VOC). The most dangerous or hazardous part, perhaps the most polluting, are the insolubles that are refined out of the sticklac and grainlac such as twigs, cocoons, leaves, bug bodies, etc. saturated with alcohol. The shellac industry is working on building huge evaporators, which will suck all the alcohol out of these insolubles so the volatility will not be an issue. Shellac flakes are all natural and non-toxic. It is the alcohol solvents that are regulated.
Quality Control :
Chemical analysis does not assist in determining the quality of shellac. More important are empirical tests such as flow and shelf life that most customers have articulated as of great concern. In addition, carefully examining the purity of the shellac by removing as many of the natural impurities found within the sticklac is of utmost importance (insolubles are defined by the undissolved matter remaining when the resinous compound is mixed with hot alcohol). All refining processes are monitored for their effectiveness in removing these undesirables