In this paper it is proposed first to give some consideration to a variety of factors which influence the enameller in selecting a frit for any particular purpose. Later, a number of these factors will be examined in more detail in order that the theoretical principles involved may be appreciated. Before selecting the type of frit to be used, the practical enameller must consider several points, usually in consultation with his frit supplier. The main factors involved are the colour to be used; whether the frit should be clear or opaque; whether special properties allied to performance (for example, acid resistance or heat resistance) are required and finally, whether the enamel is to be used on sheet iron or cast iron. In addition, there are, in some cases, special factors to be considered: surface texture may be important (for example, non-reflecting surfaces, school blackboards, etc.); or surface hardness may have particular importance. This last-mentioned property will be referred to again later. In the hollow-ware industry, the toxicity of the enamel is important where there is contact with foodstuffs and in such cases the enamels must be formulated in such a way that no poisonous material, likely to be injurious to health, can be extracted from the enamel.
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