Gemstone Treatments: A Historical Perspective

raw lapis lazuli

Raw Lapis Lazuli

Few consumers realize how common gemstone treatments are. Gemstones are regularly heat-treated, irradiated, fracture filled, laser drilled, and subjected to diffusion treatments. Examples include the following:

treated lapis lazuli

Treated Lapis Lazuli

Dyeing, Waxing, Oiling, Filling, Impregnation, or Coating—coral, diamond, emerald, lapis lazuli, onyx, opal, pearls, peridot, ruby, sapphire, and turquoise.

Heat Treatment—amethyst, aquamarine, citrine, diamond, ruby, sapphire, tanzanite, topaz, tourmaline, and zircon.

Irradiation—citrine, diamond, pearls, topaz, and tourmaline.

navajo turquoise


With regard to diamonds, Cuellar (2000) estimated that “one out of every three sold in the United States has been treated to some degree, including doublets [assembled stones], coating, and irradiation.”

raw gemstones

Untreated Gemstones

And new treatment protocols are constantly being developed. Although trained gemologists can usually spot the telltale evidence of gem treatments, there is often a critical gap between the time when a new treatment protocol is introduced and when a laboratory acquires the ability to detect that treatment.

But the truth of the matter is, gemstones have been treated for centuries. There is ample evidence, for example, that people on the Indian subcontinent heat-treated their gemstones in antiquity. The Puranas (250–1000 CE) indicate that stones can be improved by means of fire. And when Duarte Barbosa traveled to the East in the early 16th century, he noted that gemstones were put into fire for a number of hours, from which some emerged “very bright and of great value.”


Al-Biruni’s (AD 973–1048) Book on Minerology (Trans. Said, 1989) describes how rubies were heat-treated in the Near East:

“The practice is therefore, to roast the reddish [stones] so that the mixed colours are made to disappear…A ruby stone having been roasted is re-examined, and, in case it does not gain clarity, it is re-heated. Iraqi traders possessing the dark kind, desire that it should fetch a higher price. They heat it in a crucible…and the roasting process results in its becoming lighter…This process of heating is continued for a period sufficient to meld a mithqual of gold. A poultice is applied to the stones for cooling them. The stone finally cut rubycrystallizes as a clear and transparent gem, and fetches a higher price.”

ostrich treatmentAlthough this description of the ruby treatment process is almost identical to methods used today, not all recorded gem treatments were as conventional. Al-Biruni continued with the following story:

“[Concerning an] incident of a gem which belonged to a certain person. It fell from his body and an ostrich perambulating nearby happened to swallow it…It was told by someone that the ostrich had swallowed the stone…[and] at last the ostrich was killed and its gizzard laid open. It was found that the stone had become lighter and its colour clearer and more beautiful. The heat of the gizzard had performed the function of fire. This incident gained wide fame.”

Indian GoldsmithsAccording to S. M. Tagore’s Mani-Mali, a 1879 translation of ancient Indian texts,“ all gems are refined by steeping and boiling them thrice seven times respectively in the juice of ghritakumárī, little natiyá thorn, and the milk from human teats.”

diamond ring men's

The same source provided an old recipe for purifying diamonds:

“The process [of refining a diamond] is on some auspicious day to dip a diamond in the juice of a kantakári [solanum jaquiri plant] and then to burn it in a fire made by dried pieces of the dung of cow and buffalo. The burning should be carried on for a whole night; in the morning the diamond should be put under horse’s urine, and again burnt. By this process of burning being continued for seven days together, the diamond will be refined.”

three pearlsThe Papyrus Graecus Holmiensis (c. AD 300), also known as the Stockholm Papyrus, contains many recipes for creating and improving gemstones and precious metals. Below is a recipe for whitening pearls (Trans. E. R. Caley, 1926):

“Take the pieces of mother of pearl and put them into bitch’s milk. Put the cover upon the vessel and leave it there two days and two nights. Draw them out, as they lie there strung on asses’ hair, and observe whether they have become white. If not, put them in again until they become excellent in this respect. If you afterwards besmear a man with this [concoction] he becomes leprous.”

jeweler workshopIn today’s market, dealers’ attitudes vary with respect to the use of treatments, which are aimed at adding value to inferior gemstones in order to maximize profits. Regardless, ethical business practice in the gem and jewelry industry requires that sellers disclose any known treatments or enhancements—especially when they have a significant impact on the value of the gemstone. When purchasing gemstones, it is always wise to inquire about their treatment history. Do not buy from any dealer who cannot give you a complete answer.

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