=Shellac=—­or, more properly, gum-lac—­is a resinous substance obtained from the Bihar-tree, and also from the Ficus Indica, or Banyan-tree.  It exudes when the branches are pierced by an insect called the Coccus ficus.  The twigs encrusted with the resin in its natural state is called Stick-lac.  When the resin is broken off the twigs, powdered, and rubbed with water, a good deal of the red colouring matter is dissolved, and the granular resin left is called seed-lac; and when melted, strained, and spread into thin plates it is called shellac, and is prepared in various ways and known by the names of button, garnet, liver, orange, ruby, thread, etc., and is used for many purposes in the arts.  Shellac forms the principal ingredient for polishes and spirit varnishes.  Red sealing-wax is composed of shellac, Venice turpentine, and vermilion red; for the black sealing-wax ivory-black is used instead of the vermilion.  Shellac is soluble in alcohol, and in many acids and alkalies.  Lac-dye is the red colour from the stick-lac dissolved by water and evaporated to dryness.  The dye, however, is principally from the shrivelled-up body of the insect of the Stick-lac.

Shellac is produced in the largest quantity and the best quality in Bengal, Assam, and Burmah.  The chief seat of manufacture is Calcutta, where the native manufacturers are accused of adulterating it with resin to a considerable extent.  The best customers are Great Britain and the United States, though the demand in the Italian markets appears to be on the increase.

=Amber= is a yellow, semi-transparent, fossil resin; hard but brittle, and easily cut with a knife; tasteless, and without smell, except when pounded or heated, and then it emits a fragrant odour.  It has considerable lustre; becomes highly electric by friction; and will burn with a yellow flame.  It is found in nodules of various sizes in alluvial soils, or on the seashore in many places, particularly on the shores of the Baltic.  Amber is much employed for ornamental purposes, and is also used in the manufacture of amber-varnish.  It will not dissolve in alcohol, but yields to the concentrated action of sulphuric acid, which will dissolve all resins except caramba wax.

=Pumice-stone.=—­This well-known light and spongy volcanic substance is extensively quarried in the small islands that lie off the coast of Sicily.  Its porosity and smooth-cutting properties render it of great value to painters and polishers for levelling down first coatings.  Ground pumice-stone is the best for cutting down bodies of polish or varnish that are more advanced towards completion.  The best way to get a surface to a piece of lump pumice-stone is to rub it down on a flat York stone, or, better still, an old tile that has been well baked.  Pumice-stone should not be allowed to stand in water; it causes the grain to contract and to harden, thereby deteriorating its cutting properties.