Thomas Cletscher

(via Diamond Cuts in Historic Jewelry:1381-1910) Herbert Tillander writes:

Very fortunately, the majority of the sketches by Thomas Cletscher (1598-1668) have been preserved, and are now in an album in the Boymans-van Beuningen Museum, Rotterdam. The drawings themselves date from 1625 to about 1647. They cover a period of rapid development in the evolution of diamond cutting, and include illustrations of actual diamonds of newly introduced types and thus supplement the drawings of contemporary artists.

Cletscher, the son of a wealthy wine merchant, gained much of his experience from his brother-in-law, Jao Colen of Coole, Dean of te Guild of Goldsmiths. In 1650 Cletscher became a professional jeweler and was appointed to the Court of Orange. He became a gem-setter and a specialist in diamonds, and was thus in a position to reproduce with great accuracy the different diamond cuts and their facetings. His drawings and comments five exact details of outline, size, weight, faceting, provenance, and so on. Even those drawings not actually by Cletscher himself are of comparable precision and quality. What he was doing, in fact, was producing a detailed illustrated diary of his family business.

Cletscher eventually became Dean of the Guild of Gold and Silversmiths and Mayor of The Hague. He also had connections with banks and pawnbrokers, as an evaluator and an intermediary in important transactions, such as the pawning and eventual sale in Amsterdam of the British Crown Jewels by Queen Henrietta Maria.