A Treatise on Gems; In Reference to Their Practical and Scientific Value

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1838. Excerpt: ... TREATISE ON GEMS. 41 i.: i, .' lit B, The Rose-Diamond, has but a crown, and no, . collet; it is formed of equilateral triangles, and consists, y of two rows of three-sided facets; those on the girdle.., are pavilion, and the others star-facets. But there are, variations in the number of facets: the Dutch roses have, eighteen. pavilion and six star-facets; others have sis; pavilion and six star facets, or twelve pavilion and six star-facets; and some, also have twenty-four three-sided pavilion and twelve star-facets. The Rose Diamond is only that Diamond, the proportion of whose breadth, to its depth is too much extended, and which would not, without much loss, make a good brilliant. There are fragment Rose Diamonds, which are very small, and Ear-drop Roses... C, The Table-Diamond, is that stone which is very flat, and of little depth, and which reflects but little lustre: they have a table with four planes and eight facets; and, in order to make the best of their lustre, they receive a brilliant cut. D, The Bastard-Diamond, is that Diamond whose cut is mixed up from the above forms. There are a few more forms given to those Diamonds which are found unfit for any of the above cuts, such as the Thick-Stones, the Portrait Diamonds, the Senail Diamonds, which are, however, all unfit for the above cuts. XXXVI. FORM OF GEMS. The gem lapidary occupies himself not only with grinding the common and rare gems, but also pastes, fcc.: he uses likewise wheels, but of different material from those for Diamonds. His wheels are.either of copper, if for very hard stones; or of lead or pewter for softer stones; he has likewise polishing wheels. If any wheel is too soft for very hard stones, he cuts furrows in it, which are then filled out with rotten-stone o...