Enamels for metal normally used on copper work satisfactorily on good cast iron providing certain precautions are taken. Ideally the surface should be sandblasted, however in most instances it is sufficient to use an electric grinder to remove irregular surface areas such as lumps, projections, ridges, rust areas, etc. We do not recommend any casting whether it be cast iron, cast gold, cast silver, etc. be pickled. Castings usually have a few pores where the pickle solutions hide only to come out as blisters in the firing operation.
Best results are normally obtained if the firing temperature is as low as possible. Select enamels for metal which will fire at 1300-13500F for 20 minutes or more. Sifting is not an ideal method of applying the first coat. At these low temperatures individual enamel grains do not flow out easily. If the surface of the cast iron is exposed between grains of enamel it will oxidize during the long firing cycle. Although a second coat may flow out and cover the entire surface the oxidized areas may produce blisters. The best practice is to use Liquid Form – Water Base enamels for the first coat.
For small articles Thompson’s Overglaze Painting Enamel (dry powder) can be mixed with water and applied for the first coat. Cast iron does not require a cobalt bearing ground coat as described above for certain types of steel. Subsequent coats can be normal enamels for metal used on copper if they fire at these lower temperatures. They may be applied by the usual methods. Enamels for metal with expansions of about 240 to 340 are workable on cast iron.
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