Flux Fusion Process
This method was developed only in the late 1930's and has since been perfected to a great extent.
- A flux is a material that lowers the melting point of a substance with which it is mixed.
- Some materials are quite insoluble in high temperature water, but are soluble in a flux.
- The common fluxes used are lead fluoride, lithium molybdate and boron oxide.
- Flux materials have fairly toxic fumes and are also very reactive materials.
How gemstones are synthesized by flux fusion process?
- In most cases the crucibles are made of platinum, but iridium and graphite are also used.
- Powdered ingredients are mixed with the flux in a platinum crucible.
- On heating, the flux melts and becomes a powerful solvent for the other ingredients which also melts.
- Cooling and evaporation causes crystallization of the molten material with or without the use of seed crystals.
- As the growth is slow and equipment costs are high, these synthetics are expensive when compared with those by the methods discussed earlier.
Gemstones synthesized by flux fusion with its identification.
- The characteristic inclusions seen are flux fingerprints in the form veils and droplets or globules, hexagonal and / or triangular platelets, parallel growth structures or venetian blind effect, seed plate, spicules and included crystals.
- Earlier flux emeralds have a lower R.I. = 1.56 - 1.565, D.R. 0.005. Recently available flux emeralds tend to have similar R.I.'s as the natural counterparts.
- Earlier flux emeralds have a lower S.G. = 2.66. Recently available flux emeralds tend to have similar S.G.'s as the natural counterparts.
- Flux emerald with high chromium content exhibit a strong red transmission to light, appear strong red through the Chelsea filter, and appear strong red under ultra violet light.
- A few of the well known producers of these emerald are P. Gilson (France), G.F. Chatham (U.S.A), Zerfass, Lennix, Seiko and Russia.
Synthetic Corundum (Synthetic Ruby / Synthetic Sapphire):
- Synthetic corundum has similar physical and optical properties as the natural counterparts.
- Under magnification - flux fingerprints in the form veils and droplets or globules, flux droplets maybe whitish or orange (Ramaura) in colour, hexagonal and / or triangular platelets, parallel growth structures, zoning characterised by process, seed plate, spicules and included crystals.
- A few of the well known producers of these rubies are Kashan (U.S.A), Chatham, \/ocera (Japan), Lechleitner (Austria), Ramaura, Knischka, Duoros (Greece), Tairus, Russia etc.
- Synthetic spinel has similar physical and optical properties as the natural counterparts.
- Synthesized in red and recently blue varieties.
- Under magnification flux droplets and veil like flux fingerprints are seen.
- Colourless when pure (without any dopants) - diamond simulant.
- Isotropic character.
- The S.G. is 4.55 - 4.60
- Dispersion - 0.028
- Flux veils under magnification.
- Synthetic chrysoberyl has similar physical and optical properties as the natural counterparts.
- Synthetic alexandrite and synthetic chrysoberyl cat's eye have been synthesized.
- Flux fingerprints, fine dust like pinpoint inclusions and droplets are seen under magnification.
- Synthesized by Creative Crystals, Ramaura, Seiko, Kyocera (Inamori), Russia.