Sticklac is the resinous secretion of a kind of tiny insect known as Laccifer lacca.
During harvesting, the lac encrusted twigs are cut from the host plants. Then the lacs are removed from the twigs by scrapping. The lac thus obtained is known as stick lac or scrapped lac or crude lac or raw lac, that contains insect body, lac dye, sand and twig debris, in addition to resins.
The lac most commonly used across the world is shellac which is produced by any of the following processes:
(a) Indigenous Process/Country Process:
In this traditional method, the seed lac is first filled into long sausage-shaped cloth bag of about 2 inches diameter and 30 feet length. The bag is then gradu¬ally passed in front of a charcoal-fired hearth to melt the lac. By twisting the bag, the molted lac is then squeezed out through the sieve of the cloth.
This molten filtered mass is then either stretched into sheets of about 0.5 cm thick with the help of glazed ceramic cylinder, or allowed to solidify in form of dice, called button lac. The residue left inside the cloth bag contains apart from lac, sand, insect debris, and is referred to as kirrilac.
The shellac obtained by such method are available in various commercial forms like Lemon one shellac, Lemon two shellac, Superior shellac, Kusmi button lac, Light pure button lac, etc.
(b) Heat Process :
In this process, the seed lac is melted by steam heat. Oxalic acid and titanium dioxide are mixed with the melted lac at this stage. The molten lac is then squeezed through filter by means of hydraulic pressures. The filtered molten lac is drawn into long and continuous sheets with the help of roller .
These sheets are broken into pieces, called flakes. Various grades of machine made shellac flakes are available commercially, that include Orange shellac, Black T.N. shellac, Orange fine shellac, etc.
(c) Solvent Process:
In this process, the seed lac is dissolved in refrigerated alcohol and then filtered through filter press to remove the wax and other impurities. The lac thus obtained is dewaxed lac. The alcohol is then removed with the help of roller; the molten shellac is then stretched.
The solvent process may yield various grades of commercial shellac, like Dewaxed platina, Dewaxed blonde, Dewaxed lemon, Dewaxed garnet, etc.
By the same process, decolourised lac can be obtained by removing the colour (to any required standard) through charging of the dissolved lac with activated carbon.
The basic procedure of bleached shellac manufacture includes following steps:
(1) Dissolving the shellac in aqueous sodium carbo¬nate solution at 90-100°C;
(2) Stirring with sodium hypochlorite and
(3) Filtering after cooling.
The bleached shellac, thus obtained, is then reclaimed from the filtered solution with sulphuric acid. This bleached shellac is then again filtered and finally dried. The bleached lac is white in colour and com¬mercially available in two grades, dewaxed bleached shellac and waxy bleached shellac.
