Editing Gemstone (section)

==Cutting and polishing==
[[File:Diamond cutter. Amsterdam. 2012.jpg|thumb|right|A diamond cutter in [[Amsterdam]]]]

A few gemstones are used as gems in the crystal or other forms in which they are found. Most, however, are cut and polished for usage as jewelry. The two main classifications are as follows:

* Stones cut as smooth, dome-shaped stones called [[cabochon]]s or simply cab. These have been a popular shape since ancient time and are more durable than faceted gems.<ref name=":12">{{Cite web |title=A Guide to Gem Cutting Styles |work=International Gem Society |url=https://www.gemsociety.org/article/gem-cutting-terms/}}</ref>
* Stones which are cut with a [[faceting machine]] by polishing small flat windows called [[facet]]s at regular intervals at exact angles.<ref name=":12"/>

Stones which are opaque or semi-opaque such as [[opal]], [[turquoise]], [[variscite]], etc. are commonly cut as cabochons. These gems are designed to show the stone's color, luster and other surface properties as opposed to internal reflection properties like brilliance.<ref name=":12"/> Grinding wheels and polishing agents are used to grind, shape, and polish the smooth dome shape of the stones.<ref>{{cite book|title = Introduction to Lapidary|first = Pansy D.|last = Kraus|publisher = Krause Publications|date = 2007|isbn = 9780801972669|url-access = registration|url = https://archive.org/details/introductiontola00krau}}</ref>

Gems that are transparent are normally faceted, a method that shows the optical properties of the stone's interior to its best advantage by maximizing reflected light which is perceived by the viewer as sparkle. There are many commonly used shapes for [[diamond cut|faceted stones]]. The facets must be cut at the proper angles, which varies depending on the [[optical]] properties of the gem. If the angles are too steep or too shallow, the light will pass through and not be reflected back toward the viewer. The faceting machine is used to hold the stone onto a flat lap for cutting and polishing the flat facets.<ref>{{cite book|title = Faceting For Amateurs |first1= Glenn|last1= Vargas|first2= Martha|last2= Vargas|date = 2002 |publisher= G. & M. Vargas|isbn = 9780917646096}}</ref> Rarely, some cutters use special curved laps to cut and polish curved facets.