We are often asked by customers, has a gemstone been heat treated. In essence every stone has been heated in some way as they are naturally heated in creation.

The Heating Process

The heating process is in fact just a way of artificially enhancing the colour of a gemstone. It does no harm but to say a gemstone has been unheated when it has been is not being truthful. A stone that has no heat treatment can be tested and certified by a GemLab.

They are totally natural but only account for a small percentage of gemstones sold, they are usually the larger stones being a carat or two plus. 

In the late 19th century imitation of rubies and sapphires were just coloured glass and easy to tell apart from the real thing. With the invention of lasers synthetic ruby was used to emit the red light made by drawing solid crystal from a melting pot invented in 1902, called the flux method.

After a number of months the synthetic material can be used. A synthetic ruby does contain almost the same chemical properties as the natural stone but sold at a fraction of the price and are more vivid in colour. 

How To Tell The Difference 

To tell the difference is difficult and a high powered microscope needs to be used and tiny bubbles in the synthetic material can be seen and do reflect light differently. 

A Ruby is a simply crystalline aluminium oxide known as corundum and is clear when pure. But the impurity of chromium and iron gives it it’s red colour.

Today almost 95% of all rubies set into jewellery are heat treated in some way. However, these can still be very expensive up to $5000 per carat, as a good ruby in the first place has only been enhanced to bring out its natural colour.

However some natural rubies if very poor quality in the first place can have ‘flux enhancement’ and these stones are literally held together by glassy filler.
However they are quite easy to tell and if you are looking at a ruby that has been heat treated you will not seen any filler or noticeable enhancement. If it was a poor ruby in the first place no amount of heat treatment will make it perfect!

It is good to note that the Gemological Institute America and other certification authorities ACCEPT that heat treatment is perfectly normal for enhancing a natural ruby and indeed that the process is permanent and will not degrade over time. The buyer can of course insist on purchasing a ruby with no heat treatment but must have a certificate from a reputable lab that guarantees this and understands that they will pay a far higher price for a stone that in essence is not really that different from a heat treated ruby which is still a natural gemstone.

The GIA states that you should assume your ruby is heat treated as this is a common industry practice. It does not bring down the value of the stone but rubies with a report that state that there is no evidence of heat are very rare and therefore very expensive.

The GIA suggest this: To be sure you are purchasing an authentic piece, it is always best to consult a jeweller or gemologist who could use their expertise to determine the authenticity of your stone.

We at Vintage Tom/Charles Hart stand by everything we sell and you can at least be confident in the knowledge that you have purchased an item from a reputable source.

October 28, 2020 — CG Hart