Page:The chemistry of paints and painting.djvu/68



CANVAS

usual, and probably the best fibre for the manufacture of canvas for painting is unbleached flax—that is, linen; hemp and cotton are decidedly inferior. The material is woven in different ways, and with strands of different degrees of fineness, so as to produce cloths of various degrees of thickness and fineness, and having several kinds of texture and surface.

The canvas is first treated with size or a solution of glue ; this should be as free from colour as possible : the addition of honey to the size is undesirable. The priming consists of two coats, the first containing whitening and size, the second lead white and linseed oil. Fuller primings are often given where it is not desired to allow the texture of the canvas to remain evident. Such primings are put on alternately in directions at right angles to one another, and are treated in the same way as the primings of panel. If before the last priming be dry it be dusted with zinc white, or if a very thin final priming of zinc white and drying oil (free from lead) be given, the usual discoloration of the canvas which occurs on keeping it, especially in the dark, will be avoided. But such discoloration can always be removed by leaving in contact with the priming a piece of blotting-paper saturated with a solution of