ENAMELS 277 



specimens of enamelled saucepans of cast iron. Dr. Ure exposed the finely-enamelled 

 saucepans of Messrs. Konrick to very severe trials, having fused even chloride of 

 calcium in them, and found them to stand the fire very perfectly without chipping or 

 cracking. Such a manufacture is one of the greatest improvements recently intro- 

 duced into domestic economy ; such vessels being remarkably clean, salubrious, and 

 adapted to the most delicate culinary operations of boiling, stewing, making of 

 jellies, preserves, &c. They are also admirably fitted for preparing pharmaceutical 

 decoctions, and ordinary extracts. 



The enamel of these saucepans is quite free from lead. In several of the saucepans 

 which wore at first sent into the market, the enamel was found on analysis to contain 

 a notable proportion of oxide of lead. In consequence of the quantity of borax and 

 soda in the glaze, this oxide was so readily acted upon by acids that sugar of lead 

 was formed by digesting vinegar in them with a gentle heat. 



A suitable oven or muffle for lining or coating metals with enamel may have the 

 following dimensions : 



The outside, 8 feet square, with 14-inch walls ; the interior muffle, 4 feet square at 

 bottom, rising 6 inches at the sides, and then arched over ; the crown maybe 18 inches 

 high from the floor ; the muffle should be built of fire-brick, 2% inches thick. Another 

 arch is turned over the first one, which second arch is 7 inches wider at the bottom, 

 and 4 inches higher at the top. A 9-inch wall under the bottom of the muffle at its 

 centre divides the fire-place into two, of 16 inches width each, and 3 feet 3 inches 

 long. The flame of the fire plays between the two arches and up through a 3-inch 

 flue in front, and issues from the top of the arch through three holes about 4 inches 

 square. These open into a flue, 10x9 inches, which runs into the chimney. 



The materials for the enamel body (ground flint, potter's clay, and borax) are first 

 mixed together, and then put into a reverberatory furnace, 6 feet 7 inches long, by 

 3 feet 4 inches wide, and 12 inches high. The flame from an 18-inch fire-place 

 passes over the hearth. The materials are spread over the floor of the oven, about 

 6 inches thick, and ignited or fritted for 4 or 5 hours, until they begin to heave and 

 work like yeast, when another coating is put on the top, also six inches thick, and fired 

 again, and so on the whole day. If it be fired too much, it becomes hard and too 

 refractory to work in the mxiffles. The glaze is worked in an oven similar to the 

 above. It may be composed of about one-half borax and one-half of Cornish stone 

 (partially-decomposed granite) in a yellowish powder procured from the potteries. 

 This is fritted for 10 hours, and then fused into a glass which is ground up for the 

 glaze. 



The Patent Enamel Company use coloured enamel very extensively, and by the 

 use of stencil plates produce cheaply very good designs in enamel upon articles 

 of iron. Their manufacture by this process of street plates, and signs in enamel are 

 of much interest. The following are recipes for enamels in general use : 



Grey Mixture Enamel. 



Ibs. oz. 



Sand 10 



Kedlead 33 



Boracic acid 20 



Cullett 114 



Bicarbonate of soda 16 



Nitre ........ 1 2 



Manganese. ..... . 8 



194 10 

 Another is 



Ibs. oz. 



Flint . ... . . ' . '.; . 36 



Boracic acid . . . . .'>-. 24 



Bicarbonate of soda . . . . . . 24 



Nitre . . . . / . . . . 18 



102 

 White Mixture Enamel. 



Ibs. oz. 



Cullett .', ... . 11 



Boracic acid 70 



Bicarbonate of soda . . . . . .04 



Phosphate of lime 38 



Oxide of antimony , , . , , . 2 



21 14 



