412 Chemical Aids to Art. 



in a thin layer upon the wall, and when dry affords a most 

 retentive ground, which should be moistened with distilled 

 water before it is painted upon. Nearly all the good vege- 

 table colours, and many other pigments which are inadmissible 

 in the two former methods of wall painting, may be freely 

 used in this third method. Any portion of the picture not 

 fixed when dry should be syringed with the soluble phosphate 

 liquor till the desired effect is produced. Alternate syringings 

 with phosphate liquor and baryta-water are very effective 

 occasionally, but they lighten the shade of colour to which 

 they are applied considerably. This process admits of much 

 further elaboration, and, probably, of great and beneficial im- 

 provements. The soluble phosphate solution may be made by 

 boiling one ounce of the best superphosphate of lime in three 

 ounces of water : when the mixture is cold, the clear liquor is 

 poured off for use. 



A fourth process will lastly demand a brief notice ; it is not 

 essentially a new method, and can scarcely claim to be depen- 

 dent upon a chemical action, similar to those which take place 

 in the methods already described. It may be termed the 

 copal process. Mr. Gambier Parry, the well-known amateur 

 artist, has developed this method, and we shall follow his 

 directions in describing how it is to be carried out. A dry 

 wall is necessary. Ordinary plaster (not whitening), free from 

 salt, etc., is the surface on which the painting is to be executed. 

 The colours are not mixed with oi], but with a medium thus 

 made : take of white wax, four ounces by weight ; elemi resin, 

 one ounce by weight. These substances are to be melted to- 

 gether, and strained hot through muslin ; they are then to be 

 incorporated, by careful heating, with oil of spike lavender, 

 six ounces by measure ; fine copal varnish, twenty-two ounces 

 by measure. When the mixture is uniform, it is to be allowed 

 to cool, and is then ready for use. The colours should be 

 ground with it, and be preserved in covered pots. The surface 

 is prepared by saturating it with two or three washes of the 

 above medium, diluted with half its bulk of spirits of turpen- 

 tine. The colours may be thinned^ and the brushes cleaned with 

 oil of spike or of turpentine ; but all kinds of fixed oil must be 

 excluded. This process admits of the highest technical ex- 

 cellence, and, although the painted surface does not acquire a 

 rocky hardness, like that of the stereochrornic and similar 

 methods, it is certainly far less liable to change, and has a 

 more complete hold of the wall than any ordinary system of 

 applying colours. Very good examples of this method are to 

 bo seen in Mr. Parry's church, at Highnam, near Gloucester, 

 and more especially in one of the southern chapels of Gloucester 

 Cathedral. 



