Similarly we have discussed several aspects of surface diffusion treatment, a modified system, by addition of foreign elements which become choromophors used for altering and embellishing gemstones: the heat treatment.Before we move forward it will be useful to focus upon an essential aspect: the simple heating of a gemstone can greatly improve its appearance due to chemical changes in elements already present within the stone, or sometimes a combination of elements, when heated, can aid in the "healing" of fractures.
By Alberto Scarani and Paolo Minieri In previous articles we have discussed how adding Beryllium with high temperature treatments, generates a change and improvement of color in corundum.
An reducing or oxidizing environment (higher or lower oxygen percentage) will allow, as an example, the exsolution of the rutile needles band of silk with consequent improving of the transparency in milky, whitish or cloudy stones.
The procedure could enhance, reduce or eliminate the asterism phenomena visibility.
Sapphire engagement rings have been used for weddings since the 1880's and have recently been gaining in popularity.
Blue sapphire is the traditional birthstone of September and is very durable, making a sapphire ring suitable for every day wear.
The different dilatation coefficient between the stone and included crystals often produce dischoidal fractures surrounding them called tension halos which are very common to find in heated stones (photo 7). Not always reaching very high temperatures is necessary.