Enamels
Enamels, commonly used to enrich metal surfaces, are highest in chroma of the decorative materials under discussion and are to be treated with nearly as much restraint as one would use in enriching a surface with semi-precious stones, for strong hues are cheapened by excessive use. The plate in [Figure 436] has small circles filled with enamel and a large field of chased or uncolored design.
Transparent Enamels
Transparent enamels are comparable to clear glazes and the coloring medium is the same. Their preparation is difficult and therefore trade names have been given in the table of [Figure 464]. As will be seen by consulting the diagram of [Figure 464], T1, T2, T3, etc., they are all at their full value intensity. Enamels, as supplied by the trade, are much too intense for use in enrichment and consequently are applied over a coating of colorless clear enamel, technically named flux or fondant. As the thickness of coating of enamel may vary, the hue classification is to be regarded as approximate.
Plate 66
Opaque Enamels
Opaque enamels may be compared with matt glazes, for, while the texture of the surface has a distinct gloss, the enamels themselves are not so strong in hue as the transparent enamels. By referring to the diagram of [Figure 464], it may be seen that many of the opaque enamels are reduced in chroma, thus accounting for their softened hue.
Oxidation
Metals are capable of considerable change of color by the application of chemicals to the surface. Potassium sulphuret will lower the surface value of silver or copper to a rich velvety black associated with antiques. This may be removed in places naturally subjected to wear, thus varying the dead black appearance. Copper and brass may be coated with salt and vinegar or verdigris to give the surface a corroded and greenish appearance. Heating is a fugitive method of coloring and is, therefore, not considered.