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Introduction

Since the supply of fine quality rubies and sapphires is limited, many techniques have been developed to enhance their appearance. In fact, no other gem species is subjected to as many types of treatment as corundum. Heat treatment is accepted as a common practice and has little effect on value, where other treatments have considerable impact. Some rubies are worth as little as 5% of similar appearing, untreated gems.

Some of the treatments are very subtle, invisible even with a loupe or microscope. To make matters worse, many treated rubies and sapphires will have natural inclusions. You have to examine them very carefully to tell if they are treated or not. Taking the value of these gems into consideration, finding evidence of treatment can be critical.

Below is an outline of testing procedures. Though difficult, they must be used on all rubies and sapphires. First, here is a review of corundum treatments.

Heat Treatment

Silk in untreated sapphire

Stress fractures

Most corundums have rutile inclusions that are in the form of long thin crystals. These are so fine they are referred to silk. Rutile melts at a temperature slightly below that of the surrounding corundum. By heating it to the proper temperature and with…