Lac are scale insects (Laccifer Lacca) which live on trees called lac host trees where they secrete the lac resin which is scraped off and manufactured into shellac. To produce just 1 kilogram of lac resin around 300,000 insects lose their tiny lives. A scale insect is a common name for any of about 2000 insect species found all over the world that attach themselves in great numbers to plants and trees. Scale insects range from an almost microscopic size to more than 2.5 cm. They can be very destructive to trees - stunting or killing twigs and branches by draining the sap.
The life cycle of a lac insect takes about six months and consists of four stages: egg, larva, pupa and adult. With this life cycle, the lac industry obtains two lac crops each year from each tree. The brood lac containing the female lac insect is tied onto fresh new twigs of trees (lac host trees) where they thrive. Females lay up to 100 eggs which hatch out into larvae. These small red larvae, roughly 0.5mm, long crawl out of the brood lac (or mother cell) and settle on the twigs. At this stage both the male and female larvae live off the sap of the trees. They insert their long suctorial mouthpart or proboscis into the tree and draw out food. A secretion is exuded from their bodies which is in essence a protective covering to prevent an attack by predators. This secretion forms hard resinous layers which completely cover their bodies leaving small anal and breathing openings.
The insects mature into adults under this protective layer and both the male and female larvae become sexually mature in about eight weeks. Only the male insect undergoes a complete metamorphosis or transformation into another form; it loses its proboscis and develops antennae, legs and a single pair of wings. It is contained in a cell somewhat longer than the females with a round trap door through which it emerges, sometimes winged, to walk over the females, fertilising them. It then dies.
The female cell is shorter and roundish in shape and remains fixed to the twig. She retains her mouthparts but fails to develop any wings or eyes. While developing rudimentary antennae and legs, she really becomes an immobile shell-like organism with little resemblance to an insect. Females become little more than egg producing organisms. The female increases in size to accommodate her growing number of eggs. Lac resin is secreted at a faster rate and a continuous layer coalesces or grows into one body. After fourteen weeks the female contracts allowing light into the cell and lays her eggs. When the eggs hatch they emerge as larvae and the whole process begins all over again. Her ovaries contain a crimson fluid called lac dye which resembles cochineal (a colouring used mainly in the food industry and derived from dried bodies of coccus insects).
After the cycle has been completed and around the time when the next generation begin to emerge, the resin encrusted branches are harvested. They are scraped off, dried and processed to form shellac. A portion of broodlac is retained from the previous crop to produce the new crop.
India and Thailand are the main areas in the world where lac is cultivated. Over 90% of Indian lac comes from the States of Bihar, Madhya Pradesh, West Bengal, Maharashtra and Orissa. Lac insects thrive on certain trees and the principal lac host trees in India are Palas, Kusum and Ber. India exports different grades of handmade and machine made shellac as well as a limited quantity of refuse lac, namely kiri, molamma, etc. Lac production was introduced from India to Thailand where the rain-tree is the principal lac host. Thailand exports sticklac and seedlac.
After the trees have been infected with broodlac, the so-called crop requires little or no attention until harvest. When cultivated it is scraped off of the twigs. Freshly scraped shellac contains a lot of moisture and is usually left to dry before being sold. This is sold by the cultivators in small quantities in village markets to manufacturers or their agents. The quality and value of sticklac depends very much upon a variety of factors such as the host tree, the climate, whether the crop is harvested before or after the emergence of the larvae and methods of drying and storage. In India the yield of sticklac averages three quarters the weight of broodlac used. The lac scraped from the branches is known as crude lac or sticklac. Crude lac or stick-lac, consists of the resin, the encrusted insects, lac dye, and twigs. This is crushed, washed, dried to form Seedlac. Seedlac is then converted into Shellac by hand or machine.
The sticklac is crushed and sieved to remove sand and dust. It is then washed to break open the encrusted insect bodies, to wash out the lac dye and twigs. Decaying bug bodies turn the water a deep red. The remaining resin is dried, winnowed (fanned and separated) and sieved to get the commercial variety of seedlac. The dusty lac eliminated by sieving is known as molamma lac or refuse lac.
Traditionally seedlac is processed by hand. Seedlac is filled into a long narrow cloth bag, heated by a charcoal fire and forced out leaving impurities such as insect bodies or twigs inside the bag. The residue left inside the cloth bag is another variety of refuse lac known as Kirilac. The filtered mass is drawn into sheets appoximately 0.5cm thick and thinner by skilled workmen and made into different varieties that constitute commercial shellac e.g. Lemon I Shellac, Lemon II Shellac, Buttonlac and Standard I Shellac. Shellac varies in colour from yellow to deep orange. When bleached it is called white shellac.
Machine made Shellac is produced either by melting by steam heat and squeezing the soft molten lac through filter by means of hydraulic presses; or using solvents. Machines, rather than the traditional hand processing are being increasingly used by the lac Industry.
Shellac has been utilised in the manufacture of many products over the years. In fact 78rpm records were made from it and this was formerly the largest single outlet for shellac. It used to colour Indian solders' uniforms and is still used to dye oriental carpets. Today shellac is used in paint and varnish, as a hat stiffener, a glaze for fruit, coffee beans and nuts, a coating for tablets, as a leather dressing, as a component in rubber compounds, as a sealing wax, to make gasket cement, as a mould for dental plates, as printing ink, in cosmetics such as hair lacquer, in confectionery such as chocolate, as a food colouring, as a sealant or as a glossy silky finish on superior quality playing cards. In America large quantities of bleached shellac are used for floor polishes especially the No-Rub polishes.
Whilst shellac had been displaced almost completely by synthetic resins, the public's incessant need for anything 'natural' may be encouraging a comeback. Shellac is non toxic and can be used in food as well as non-food products. It has a tenacious adhesive quality sticking to anything from porous wood to glossy smooth surfaces. It dries to the touch in under fifteen minutes thus eliminating drips. It can be softened and moulded like clay or dissolved in solvent and spread whisper thin.
In a strange squirk of fate, shellac could be called the parent of the modern plastics industry because in the attempt to produce a resin resembling lac, we saw the beginning of plastic as we know it today.