Faceting

Reading this article https://orchid.ganoksin.com/t/gemlab-heat-treating-sapphires-from-the-anakie-district-australia/5853 seems to indicate dark Australian sapphires can be lighted by heat treatment.

This article was originally written by Ted Themelis and the testing was done around specifically sapphires from the Anakie fields.

Heat treatment generally increases the value of sapphires. That is not personal opinion but dictated by the market. A dull lifeless sapphire can be brought to life by a little heat treatment, other wise it is little more than a stone. A sapphire trader is not going to pay to reduce the value of his stone. And anyone buying an investment stone would not do so with out professional advice and testing.
I don't believe heat treatment alone would not kill the gem trade. It's been around a long time, over 800 years in fact.

How to make a stone white on one side, and red or blew on the other.
I have seen precious stones thus made, and in great esteem with great persons, being of two colours; on one side a Saphire, and on the other a Diamond, and so of divers colours. Which may be done after this manner: For example, we would have a Saphire should be white on one side, and blew on the other; or should be white on one side, and red on the other: thus it may be done. Plaister up that side which you would have red or blew, with chalk, and let it be dryed; then commit it to the fire, those ways we spoke of before, and the naked side will lose the colour and turn white, that it will seem a miracle of Nature, to those that know not by how slight an art it may be done.

John Baptist Porta, Natural Magick, 1658

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The treatment is not that hard to detect and allows a lot more people to own a sapphire in the colour it is usually associated with. Or any other colour they wish.

And with out heat treatment we would not have stones like tanzanite available. At least not in marketable quantities.

SneakyCuttlefish said:

This is the reason why I like garnets so much. No one bothers to make them or treat them and most treatments are ineffective anyway. All natural. Tsavorites for the win!

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Not correct. Plenty of simulants out there for garnets including man made ones like GGG and YAG. Nanositol is one and green CZ and YAG is often used for Tsavorite. They will even go as far as tumbling the simulant to give the impression of it being a water worn pebble. Even the pro's get fooled.
A look over some of the respected gem dealers will give an indication of what you can expect to pay and in what weight.

If the price is to good to be true, it probably is. Especially regarding Tsavorite.

To be fair, I'd say there is a difference between simulants and synthetics - a synthetic (my interpretation) is an exact replica of the natural mineral and thus is chemically identical. A synthetic sapphire practically is a sapphire, just one that was "made in a test tube rather than in a volcano" so to speak.

A simulant may have no known natural counterpart - in that case it's not so much a copy of something that exists in nature but a whole new invention. GGG, YAG, Nanosital and Cubic Zirconia do not actually match the chemical composition of your typical naturally-occuring garnet. GGG and YAG may have the word "garnet" in their name but can be used to simulate a wide variety of naturally-occurring gemstones.

It's possible that someone has made a synthetic garnet which by definition would be chemically identical to natural varieties - eg, iron aluminium silicate, magnesium aluminium silicate etc but I'm not aware of it.

I know, this is a bit of a matter of interpretation

Lefty said:

To be fair, I'd say there is a difference between simulants and synthetics - a synthetic (my interpretation) is an exact replica of the natural mineral and thus is chemically identical. A synthetic sapphire practically is a sapphire, just one that was "made in a test tube rather than in a volcano" so to speak.

A simulant may have no known natural counterpart - in that case it's not so much a copy of something that exists in nature but a whole new invention. GGG, YAG, Nanosital and Cubic Zirconia do not actually match the chemical composition of your typical naturally-occuring garnet. GGG and YAG may have the word "garnet" in their name but can be used to simulate a wide variety of naturally-occurring gemstones.

It's possible that someone has made a synthetic garnet which by definition would be chemically identical to natural varieties - eg, iron aluminium silicate, magnesium aluminium silicate etc but I'm not aware of it.

I know, this is a bit of a matter of interpretation

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Definitely agree and SC is right, no one bothers to make them. But there are many out there imitating the garnets to catch the unwary. To assume a stone being sold as garnet is a natural garnet is a risk.
If one is willing to fake a 'cheap' gem like amethyst or ametrine. Simulated garnets, esp Tsavorite are definitely a viable option for fraud. And I'm sure a respected rough dealer like Steve Ulatowski of new era gems would know what prices to charge for quality rough.