The flame temperature generally ranges from about 1000☌ to 2400☌ since the melting point of corundum is approximately 2050☌. This pedestal is lowered slowly to allow cooling and crystallization of the corundum boule. This powder drops through the oxy-hydrogen flame, melts and falls on a rotating pedestal, where it solidifies. The alumina is placed in a container or hopper which is tapped from above by a hammer at regular pre-selected intervals and regulates the flow of powder.
This requires a highly purified alumina which is prepared by repeated crystallization and later calcination of ammonium alum. This method is based on the melting of very finely pulverized alumina in an oxy-hydrogen blowpipe type burner.
Radioactive bombardment is used much less often for strengthening the yellow colour of sapphire and the creation of an orange tint in pink chromium-rich stones, which is characteristic for padparadscha sapphires.Verenuil Or Flame fusion is one of the first methods used to produce synthetic gemstones, initially for corundum, thereafter for a number of other gemstones. Sometimes they are produced by beryllium diffusion: usually shows a yellow-orangy rim – pink core when immersed. Synthetic padparadscha sapphire crystals grow submerged in a slowly cooling high-temperature liquid and have unusually high perfection and very good brilliance when cut or faceted to make loose gemstones. There are several treatments for Padparadscha.
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