This section is from the book "Cassell's Cyclopaedia Of Mechanics", by Paul N. Hasluck. Also available from Amazon: Cassell's Cyclopaedia Of Mechanics.
To treat white enamel to prevent it setting too quickly, it should be thinned with the same varnish as is used in making it. To enamel successfully, get a good flat ground to work upon, and do not try to improve the work by giving a second coat of enamel if the first does not turn out well. Never put a bright on a bright; the correct way is to finish a gloss on a flat, or a flat on a gloss. In the case of spoiled work, the work should be rubbed down with ground pumice-stone, flatted, and then enamelled again. Enamelling should be done in a warm room. All enamels become ropy if exposed to the air; keep well corked, therefore, and pour out for use only a small quantity at a time.
 
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