(via Diamond Cuts in Historic Jewelry:1381-1910) Herbert Tillander writes:
Various Gothic diamonds are documented as being ‘faceted’ without any further detail. Some of these must have been stones with flat bases and domed faceted tops. As always, the shape of the original crystal was large responsible for the shape into which the diamond was cut. A favorite cut was the Shield, for which the rough was probably a piece accidentally cleaved from a crystal such as rhombic dodecahedron or the trisoctahedrally developed face of an octahedron. The shapes of the crystal system to which diamonds belong have most of their octahedral faces slightly raised in curved triangular form and can easily be fashioned into Chiffres after an initial cleaving operation.
This type of three-faceted shield-shaped diamond has been known at least since the early fourteenth century, and is still occasionally produced today, though only in very small sizes. It is now termed the Chiffre Cut after the word ‘cipher’, the arithmetical symbol for nought. It is the least expensive type of cut—a rounded, flattish, triangular pyramid. The term Shield Cut is reserved for historical gems. William Jones illustrated a ‘decade-ring’, its head decorated all over with three and four facet Shield Cuts.
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