should be of the consistency of thick cream, and should run from the brush on being raised from the pot in one thread; if it run in several, it is too thin. If too thick, add more size and water; if too thin, more whiting. The pots used are the common red paint-pots. VARNISHING. Varnish is a solution of resin in oil or spirits of wine.[122] Surfaces which are to be varnished should be of the greatest smoothness and polish which it is possible to attain. Dark colours are best calculated for varnishing; the lighter colours, such as sky-blue, apple-green, rose-colour, delicate yellow, &c., will not bear varnishing so well, and in spite of the greatest care are liable to get dirty. The best preparation for stopping suction in absorbent surfaces, and so rendering them fit to take varnish, is made of isinglass or parchment size; for the darker colours it may be made of common clear glue. Four or five coats will be necessary for the brighter colours; two or three will be sufficient for the darker ones. Great care must be taken not to wash up water or distemper colours in laying on the first coat, nor to lay on a second coat before the first is perfectly dry; nor must the varnishing be proceeded with before the last coat of size is thoroughly dry. Varnish may be applied on surfaces brought forward in oil without any special preparation, provided the oil has become thoroughly dry and hard. This process serves both to enhance and preserve the beauty of the colours, and in some degree to counteract the destructive influence of the atmosphere and of insects. Varnishes suitable for the work in hand, such as clear copal spirit varnish, oil copal varnish, white hard varnish, &c., may be procured from any one who supplies drawing materials. The varnishing itself requires some little care. It should be performed in a place perfectly free from dust, in a bold manner with large brushes, steadily, rapidly, and uniformly, not returning too frequently to the same spot, more especially when using spirit varnish, which loses its fluidity much sooner than oil varnish. Whichever varnish is used, it should be very thin: if spirit varnish, the room must be of a moderate temperature; for if too cold, the varnishing is apt to be rough, white, and unequal; if too hot, it is liable to have air-bladders, and to crumble and spoil. Oil varnishing may be done in a room of warmer temperature. A second coat of varnish must on no account be laid on before the first coat is quite dry. If the work is to be polished, the spirit varnish must be applied from five to eight times, oil varnish three or four; but if the work is not to be polished, then four coats of the former and two of the latter will generally be found sufficient.