254 ART OF BUILDING. 



with a wooden mould, a different cement is used ; it con- 

 sists of fine stuff, as above three fifths, and plaster of par- 

 is one fifth, mixed with a proper quantity of water. But 

 a small quantity should be made at a time, as it sets 

 very quickly. Where great expedition is required the 

 same stuff is used for other plastering. 



Plaster of Paris, known also by the names of gypsum, 

 and sulphate of lime, is an important material in plaster- 

 ing. The best method of preparing this substance for 

 the use of the plasterer, is to select the purest kinds and 

 burn them in a proper place, by which means the 

 water and sulphuric acid are driven off, after which the 

 stones are powdered fine, when it is fit for use. Care 

 is requisite in the calcination ; too much or too little 

 injures its qualities, and causes it to become soft on 

 exposure to the air. It is known to be well burned, if, on 

 mixing it with water, it has a soapy and sticky feeling to 

 the fingers. If it has not these qualities it is not worth 

 using. As burnt plaster looses its qualities by exposure 

 to the air, it should be used fresh ; and in places which 

 do not furnish this material, this stone should be procured 

 and calcined as wanted. 



Stucco is a very neat kind of work, and is principally 

 used for the interior of buildings in this country ; in France 

 and Italy it is used also for covering the exterior, but 

 this kind of work will not bear the cold of our climate 

 for exterior decorations. 



Various cornices and ornaments are formed of this sub- 

 stance for interior decorations, by means of moulds made 

 of wood ; Basso-relievos and friezes are made of the same 

 material by casting them in wax moulds ; these moulds 

 are made from clay moulds, by forming the latter by hand 

 and then running melted wax into them. The capitals 

 of columns are formed in the same manner, only requir- 

 ing numerous moulds to complete them. 



Fresco-painting or staining, is sometimes applied to out- 

 side walls to give them the appearance of stone, and is 

 performed in the following manner. The walls are 

 first covered with Roman cement, after which they are 

 washed over with a mixture of diluted sulphuric acid 

 and^water, to which a fluid-ochre of the required tint 

 is added : by this means the color is fixed and permanent, 



