Absorbent Surfaces

In the arts , these are usually rendered non-absorbent, preliminary to their being bronzed, gilded, painted, or varnished, by giving them one, or more, coats of thin size, so as to destroy their porosity; care being taken to allow each coat to become thoroughly dry before the application of the next one; and also, finally, to remove any unabsorbed exce of size from the surface, by means of a sponge dipped in warm water. This applies to ALABASTER , PAPER , WOOD , PLASTER CASTS , .; and to WALLS and CEILINGS which are not exposed to the weather, and which there is not time to prepare with drying oil. See Bronzing , Maps , Varnishing , . Absorption and consequent adherence in porous moulds, as those of plaster, are usually prevented by thoroughly saturating the pores of the mould with melted tallow, or a mixture of tallow and bees’ wax; or for delicate objects or the electrotype, with white wax. The ‘dry moulds’ are either heated before the application of these substances, or they are boiled in them; any portion that may finally remain unabsorbed, being carefully removed with cotton-wool or a soft rag. Another method is to wash the moulds over two or three times with drying oil, or to boil them in it; after which they must be exposed to the air for some days, to dry and harden. Before being used for plaster, composition, ., the surface of these prepared moulds require to be slightly moistened with sweet oil. Plaster moulds are generally prepared for sulphur, wax, and gutta perch a casts, by simply placing them (upright) with the back immersed in a little water, contained in any shallow ve el, as a saucer or plate; and letting them remain there until moisture begins to appear on the surface. The materials to be cast, or moulded, should then be used at the lowest po ible temperature, to prevent the formation of air-bubbles. The adherence of wax or mixtures containing it, and of gutta perch a, is best prevented by moistening the surface of the mould (whether of plaster, metal, or gutta perch a), immediately before use, with soft soap reduced to the consistence of thin cream with water. See Casts , Moulds , Electrotype , .