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Encyclopedia Britannica - Main :: KRO-LAP |
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LAC , a resinous incrustation formed on the twigs and young
insect
appearance with every successive generation. Lac is a product of the East
Pegu
insect
kermes
young
separate
great
appearance , the females develop into a singular amorphous organism consisting in its main features of a large smooth shining crimson-coloured sacthe ovarywith a beak stuck into the bark, and a few papillary processes projected above the resinous surface. The red fluid in the ovary is the substance which forms the lac dye of commerce. To obtain the largest amount of both resin and dye-stuff it is necessary to gather the twigs with their living inhabitants in or near June and November. Lac encrusting the twigs as gathered is known in commerce as "stick lac"; the resin crushed to small fragments and washed in hot water to free it from colouring matter constitutes " seed lac "; and this, when melted, strained through thick canvas, and spread out into thin layers. is known as " shellac," and is the form in which the resin is usually brought to European markets. Shellac varies in colour from a dark amber to an almost pure black; the palest, known as " orange-lac," is the most valuable; the darker varieties " liver -coloured," " ruby," " garnet," &c.diminish in value as the colour deepens. Shellac may be bleached by dissolving it in a boiling lye of caustic potash and passing chlorine through the solution till all the resin is precipitated, the product being known as white shellac. Bleached lac takes light delicate shades of colour, and dyed a golden yellow it is much used in the East
in sealing-wax, and forms the basis of some of the most valuable varnishes, besides being useful in various cements, &c. Average stick lac contains about 68 % of resin, 10 of lac dye and 6 of a waxy substance. Lac dye is obtained by evaporating the water in which stick lac is washed, and comes into commerce in the form of small square cakes. It is in many respects similar to, although not identical with, cochineal. End of Article: LAC If you wish, you can link directly to this article.
<a href="http://jcsm.org/StudyCenter/Encyclopedia/KRO_LAP/LAC.html"> LAC </a> |
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