[Article] "Blue lava" - Indonesia
E107 Introduction to Gemstones This poster begins by showing the most popular gemstones, grouped together by class. It explains the important "Four C’s" of gemstones - Cut, Clarity, Color and Caret, followed by an introduction to other important qualities, such as Asterism, Opalescence, Hardness and Pattern. The next row provides wonderful illustrations of the important gemstone cuts, accompanied by an explanation. This is followed by an introduction to cabachons. It then presents an as
The diagram below and opposite shows gemstone cuts from antiquity to the present. True 'artists in stone', lapidary has evolved over thousands of years. During antiquity, cabochons were initially the only cutting style available. Guided by the natural facets of the gemstone's crystal structure, the lapidary cut gems in increasingly more complex ways over time. The earliest of these involved removing the tops of crystals. In the last hundred years, technological advances have allowed cutters to d
The round brilliant cut possesses the angles and proportions once thought necessary to display a Diamond's best dispersion (fiery flashes of colour), scintillation (play of light) and its characteristic brilliance (white light reflections). While also used for other gemstones, the brilliant cut was developed specifically for Diamonds. The standard number of facets in a round brilliant cut is 57 (or 58 if you include the culet).
Plate 1: Brilliant Forms. 1 a, b, c, Double-cut. 2 a, b, c, English double-cut (double-cut brilliant with star). 3 a, b, c, Triple-cut, old form. 4 a, b, c, Triple-cut, new form round. 5 b, c, The same oval. 6 b, c, The same, pear-shaped. 7 a, b, c, The same triangular. 8 a, Half-brilliant.
Plate 3: 1-8 Rosetts (Rose-cut). 1 b, Rose, round. 2 b, Rose, pear-shaped. 3 a, Dutch Rose. 4 a, Brabant Rose. 5a, 6 a, Roses of other forms. 7 a, b, Rose recoupeée. 8 a, b, Cross-rose. 9 a, Double rosette (pendeloque). 10 Briolette. 11 a, b, Table-stone. 12 a, 13 b, Thin-stone. 14 a, b, Table-stone, with brilliant form above. 15 a, b, 16 b, Thick-stone. 17 b, Cabochon, simple (hollowed). 18 b, The same with facets. 19 b, Double Cabochon.
Plate 2: Star and step cuts: 1a, b, c, Star-cut (of Mr. Cair). 2, a, b, Step-cut, four-sided. 3 b, Step-cut, six-sided. 4 b, c, Step-cut, eight-sided. 5 a, b, Mixed-cut. 6 a, b, Cut with double facets. 7 a, b, c, Cut with elongated brilliant facets. 8 a, b, c, Maltese cross cut.