462 OILS, ETC., USED IN THE PAINTING OF PICTURES. 



bind it to the canvas. This may happen with one pigment, but not 

 with another, if in the original grinding more oil has been necessary 

 to get a good consistency. 



Having now dealt with the more important diluting mediums, we 

 will consider next the question of varnishes. A very large variety 

 of gums or resins are now available for varnish making, but the num- 

 ber used for artists' purposes is not great. 



Varnishes may be conveniently grouped into two divisions — the one 

 called spirit varnishes and the other oil varnishes. The spirit var- 

 nishes are prepared from the softer and more soluble gums by dissolv- 

 ing them in some medium which will evaporate and leave a layer of 

 pure resin behind, such as turpentine, alcohol, or petroleum. The 

 varnish artists are most familiar with is prepared by dissolving gum 

 mastic in turpentine. By evaporating, a layer of mastic is left be- 

 hind. Shellac- is usually dissolved in alcohol, and there are also 

 petroleum varnishes in use. 



Such spirit varnishes are brittle, weak, and easily dissolved or re- 

 moved. They should therefore form no part of the body of a picture, 

 but may be used to varnish a completed picture when thoroughly hard, 

 mostly as a protective transparent coating, which can be easily removed 

 without injuring the painting beneath. Mastic varnish, for instance, 

 can be removed by lightly rubbing with the tips of the fingers, the 

 powder of the resin largely assisting. They are apt to bloom, in 

 which case the bloom can be removed by a damp cloth, and some hold 

 that they tend to crack the picture beneath; I have found no proof 

 of this, however. 



We next come to the oil varnishes. Oil varnishes are or should be 

 made of the harder gums which will not dissolve freely in turpentine 

 or alcohol. To make an oil varnish the gum is fused and the hot oil 

 added, and the whole heated until a drop placed to cool in a glass 

 plate cools clear. It is then diluted Avith turpentine. To prevent too 

 slow drying a drying oil may be used, or driers added, and heated 

 with the varnish. While thus the fundamental process is simple, in 

 practice great technical skill is required. But again, either manga- 

 nese or lead driers can be used, and I advise for artists' use manganese 

 driers, although the varnishes so prepared do not in my experience 

 dry so quickly. The number of gums available, their means of sup- 

 ply, names, and properties form a large and confusing subject, 

 esj^ecially as no fixed and clear nomenclature has been arrived at. 



For artists' purposes a hard gum should be utilized, such as Zanzi- 

 bar or Sierra Leone copal, or the hard kauri gum from New Zealand. 

 Carefully selected pieces, light in color, should then be carefully 

 fused and incorporated with pure linseed oil. Amber is a very hard 

 gum of high melting point. The main trouble in using it is the 



