11. A process of darkening the surface of metal by the application of chemicals. Potassium sulphite will supply a deep, rich black to silver and copper. Rendering--see Planishing.
The eleven processes mentioned above are among those which, by recent common practice, have become familiar to the craftsman in precious metals. While they do not cover the entire field, they at least give the beginner an opportunity to design intelligently in terms of the material.
[Sidenote: Dependent Surface Enrichment for Pins]
Plate 53 is mainly the enrichment of the flat plane by the addition of semi-precious stones (process six). Whatever surface enrichment is added to this design becomes _dependent_ enrichment and quite analogous to _dependent_ contour enrichment, Plate 29, inasmuch as it has to be designed with special reference to the shape and character of the stone. Figures 358 to 363 are examples of _dependent contour_ enrichment; Figures 364 to 371 are examples of _dependent surface_ enrichment. Figures 358 to 367 are based upon _vertical_ inceptive axes as appropriate to their intended service. The point of concentration may be located at practically any point on this inceptive axis, provided the major axis of the stone coincides with the inceptive axis. The best results are obtained by placing the stone a little above or below the exact geometrical center of the primary mass.
[Illustration: SURFACE ENRICHMENT OF SMALL PRIMARY MASSES IN PRECIOUS METALS
CONTOUR AND SURFACE ENRICHMENT APPLIED TO FOBS
MAINLY FULL SURFACE ENRICHMENT BASED UPON VERTICAL INCEPTIVE AXES
Figures 368 to 372 show articles based upon a horizontal inceptive axis. The stone, in accordance with formal balance, is in the geometric center from left to right. One notices the important fact that the surface enrichment must bring the stone and contour together in sympathetic relation and, at the same time, be related to both stone and contour. This again brings out the meaning of _dependent_ surface enrichment. The contour enrichment is to be kept as simple as possible and the interest concentrated upon the surface enrichment. The _accentuation of both surface and contour enrichment_ in a single design marks the height of bad taste in design.