Editing Gemstone (section)

==== Verneuil flame fusion process (melt process) ====
[[File:Verneuil process diagram.svg|thumb|Verneuil furnace]]
The flame fusion process was the first process used which successfully created large quantities of synthetic gemstones to be sold on the market.<ref name="Scheel-2000">{{Cite journal |last=Scheel |first=Hans J |date=2000-04-01 |title=Historical aspects of crystal growth technology |url=https://www.sciencedirect.com/science/article/pii/S0022024899007800 |journal=Journal of Crystal Growth |language=en |volume=211 |issue=1 |pages=1–12 |doi=10.1016/S0022-0248(99)00780-0 |bibcode=2000JCrGr.211....1S |issn=0022-0248 |access-date=April 15, 2023 |archive-date=April 15, 2023 |archive-url=https://web.archive.org/web/20230415031315/https://www.sciencedirect.com/science/article/pii/S0022024899007800 |url-status=live }}</ref> This remains the most cost effective and common method of creating corundums today.

The flame fusion process is completed in a Verneuil furnace. The furnace consists of an inverted blowpipe burner which produces an extremely hot oxyhydrogen flame, a powder dispenser, and a ceramic pedestal.<ref name="Read-1999">{{Cite book |last=Read |first=Peter G. |title=Gemmology |date=1999 |publisher=Butterworth-Heinemann |isbn=0-7506-4411-7 |oclc=807757024}}</ref> A chemical powder which corresponds to the desired gemstone is passed through this flame. This melts the ingredients which drop on to a plate and solidify into a crystal called a ''boule''.<ref name="Read-1999"/> For corundum the flame must be 2000&nbsp;°C. This process takes hours and yields a crystal with the same properties as its natural counterpart.

To produce corundum, a pure aluminium powder is used with different additives to achieve different colors.<ref name="Read-1999"/>

* Chromic oxide for ruby
* Iron and titanium oxide for blue sapphire
* Nickel oxide for yellow sapphire
* Nickel, chromium and iron for orange sapphire
* Manganese for pink sapphire
* Copper for blue-green sapphire
* Cobalt for dark blue sapphire