This section is from the "Henley's Twentieth Century Formulas Recipes Processes" encyclopedia, by Norman W. Henley and others.
All constituents of which an enamel glaze is composed must be intimately mixed together. This can only be done by reducing each to a fine powder and thoroughly stirring them up together. This part of the work is often carried out in a very superficial manner, one material showing much larger lumps than another. Under circumstances such as these it is absurd to imagine that in fusion equal distribution will take place. What really happens is that some parts of the mass are insufficiently supplied with certain properties while others nave too much. A mixture of this class can produce only unsatisfactory results in every respect, for the variations referred to will produce variations in the completeness of fusion in the viscous character of the mass, and in the color.
The mixing can be done by thoroughly stirring the various ingredients together, and a much better and cheaper system is mixing in rotating barrels or churns. These are mounted on axles which rest in bearings, one axle being long enough to carry a pulley. From the driving shaft a belt is led to the cask, which then rotates at a speed of from 40 to 60 revolutions per minute, and in about a quarter of an hour the operation is complete. The cask should not exceed the 5-gallon size, and should at no time be more than two-thirds full. Two casks of this kind give better results than one twice the size. The materials are shot into the cask in their correct proportions through a large bung hole, which is then closed over by a close-fitting lid.
For gray or fundamental coatings:
Almost any kind of
glass.......... 49 per cent
Oxide of lead..... 47 per cent
Fused borax...... 4 per cent
Glass (any kind).. 61 percent
Red lead......... 22 per cent
Borax........... 16 per cent
Niter............ 1 per cent
Quartz.......... 67.5 per cent
Borax........... 29.5 per cent
Soda (enameling). 3 per cent The above is specially adapted for iron pipes.
Frit of silica powder............ 60 per cent
Borax........... 33 per cent
White lead....... 7 per cent
Fused and then ground with— Three-tenths weight of silica frit. Clay, three-tenths weight of silica frit. Magnesia, one-sixth weight of white lead.
Silica............ 65 per cent
Borax........... 14 per cent
Oxide of lead..... 4 per cent
Clay............ 15 per cent
Magnesia........ 2 per cent
No. V gives a fair average of several mixings which are in use, but it can be varied slightly to suit different conditions of work.
 
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