the Substances employed in Pottery. 489 



For the following analysis of a blue cobalt calx, I am in- 

 debted to Mr. John Adam : — 



Silica 17-84. 



Peroxide of cobalt 19'42 



Peroxide of iron 25*50 



Water 8'41 



Carbonate of lime and magnesia . 28'45 



99-62 



The oil that is used for mixing with the colours, is made 

 by boiling the following substances together; viz. linseed oil, 

 rape oil, sweet oil, rosin, common tar, and balsam copaiba in 

 various proportions. 



III. It is but recently since a new method has been applied 

 to cause the colours to flow or spread over the surface of the 

 ware. This object is effected by washing the saggars in which 

 the ware is placed previous to its being fired in the glost kiln, 

 mth a mixture of — 



1. Lime, common salt, and clay slip. Dry flows are also 

 used, which answer equally well, the mixture being sprinkled 

 on the bottom of the saggar. The following are some of those 

 flows: — 



2. Lime, sal-ammoniac and red lead. 

 S. Lime, common salt, and soda. 



4. Whiting, lead, salt and nitre. 



5. But there is a wash made of lime, clay slip, nitre, salt, 

 lead, in general use for washing all the saggars employed in 

 the glost kiln, which fuses on the inner surface of the saggar, 

 making it perfectly close and not porous, otherwise the gloss 

 required on the surface of the ware would not be obtained. 



IV. The colours used in producing the dipt or sponged 

 ware are of a very cheap kind, as it is only for common pur- 

 poses that they are employed. The colours when used for 

 dipt ware are put on the ware before it is burned ; and when 

 used for sponged ware, are put on the ware in the biscuit 

 state. The following are some of those colours : — 



L A black dip is made from manganese, ironstone and 

 clay slip. 



2. A drab dip by nickel and slip. 



3. A sage or a greenish-blue dip by green chrome and slip. 



4. A blue dip by cobalt and clay slip. 



5. A yellow dip by yellow clay alone, or a compound of 

 white and red clay, which produces the same results. 



6. A red dip is produced from the red or brown clay ; but 

 it is not every quality of this clay that will answer, as it re- 

 quires to burn red. 



The first four of these dips are prepared by mixing a little 



