ART OF BUILDING. 255 



because the acid unites with the iron which is in the 

 cement, and fixes the color. 



There is a distinct branch of plastering invented, and 

 much used in Italy, and from thence introduced into 

 France and England, where it is much used for interior 

 decorations, it is called scagliola from the Italian word 

 scaglia (a chip of marble) ; it is sometimes called mar- 

 blitur, from its imitating marble. This kind of work is 

 principally used for columns and pilasters (half columns) ; 

 for this purpose a frame of wood is made and lathed 

 about 2^- or 3 inches less in diameter than it is intended 

 to be when furnished ; the lathes are covered with com- 

 mon plastering mortar. When this is pricked up or 

 roughened by crossing it with a lathe, so as to make the 

 next coat stick, and is sufficiently dry, the worker in 

 scagliola commences. 



In preparing the materials for this kind of work, the 

 purest plaster of paris is necessary, and should be 

 reduced to a fine powder : it is mixed with a solution 

 of glue, isinglass, &c. In this solution the required 

 colors are mixed, and when the work is to be of several 

 colors, they are mixed separately, and afterwards min- 

 gled and combined as required. It is floated like other 

 plastering by means of proper moulds: after which it is 

 polished with pumice stone, it is then rubbed with tri- 

 poli, (a good kind of rotten stone) charcoal, and a piece 

 of linen, afterwards with a piece of felt dipped in a 

 mixture of oil and tripoli, and finally with pure oil. 



In this way the most precious marbles and other costly 

 stones are imitated with astonishing and delusive effect ; 

 as the imitation takes as high a polish, and feels as cold 

 and hard as the most compact marbles, nothing beyond 

 actual fracture can possibly discover the deception. If 

 the capitals of columns are made of real marble, the de- 

 ception is beyond discovery. If not exposed to frosts 

 and moisture, its durability is little inferior to that of mar- 

 ble, it retains its polish as well, and is not one tenth of 

 the expense of the coarsest kind of marble. 



In plastering the walls of buildings constructed of 

 stone or brick, the cement or plaster should never be laid 

 upon the stone or brick, if it is, the building will always 

 be damp ; therefore, the plastering should be placed on 



