The Story Behind the Stone: Assume Heat

When looking at gemstone reports, one might see the notation “assume heat” on the document. Ruby in particular is known to be subjected to this ancient treatment.

No Heat Means Top Dollar

Ruby, a member of the corundum family of minerals has been a desirable gemstone for eons. When it shimmers in its vibrant red glory straight from the mine, it commands top dollar. And when it goes to auction, there’s likely to be a serious bidding war to secure this ‘no heat’ variety. “No heat” ruby’s high price reflects both its desirability and its scarcity with serious collectors.

All Ruby – All Treated

Today, experts may assert that virtually ‘all’ rubies coming to market have been heated. Assume heat treatment is the phrase applied to ruby products whether or not the vendor has documented their provenance.

But for most of the material being found that lacks the splendid ruby-red tint, heating it to bring out its optimum beauty is the way to go. Performing this process means that more truly beautiful goods are available in the marketplace. A consumer will pay up to 50% more for heat treated stones than those less attractive untreated ones, but the post-treatment colors are worth it.

Not a New Treatment

History records that early Arab and other Middle Eastern traders were heating corundum as far back as 1240 AD. So they knew a thing or two about the beauty treatment for ruby to make a sale.

The reason corundum – both sapphire and ruby – is heated is to alter its color to a more desirable hue or improve its clarity. Some rubies have naturally occurring silk-like inclusions which dissolve under heating. But since not all ruby is produced with this silk, seeing none under the microscope is not necessarily proof that it was heated.

Not all heat treatment is the same however, and those conducting this method have certain goals in mind prior to its treatment. For example, rubies that are cooked above 1,100 °C or 2012 °F, are done to remove unwanted brown, purple, or purplish tones in the crystals. Firing these stones above 1,450 °C, or over 2,642 °F, will also dissolve those fine rutile silk inclusions. In some cases, this heating also improves the stone’s transparency.

Change with New Discoveries

Mozambique rubies have become popular today for those wanting the true lipstick red tint of ruby. Since about 2009, Mozambique ruby has taken lead in providing the global supply of fine quality ruby. Stones from this region may undergo routine high temp heating. But insiders also have pointed to Mozambican stones being sent to Sri Lanka (and maybe Bangkok) for heating at much lower temps. The result, they say removes any blue color within the crystals and produces that desired pure red hue.

Nothing to Hide

Irrespective of what temperature ruby has undergone in its heating, this procedure is an industry accepted form of gemstone treatment to increase salability through more attractive color stones. Since corundum – ruby or sapphire were initially formed under conditions of extreme heat, some professionals say the additional heating is merely a continuation of what nature was doing to these crystals.

Heating rubies is a permanent and stable treatment. And it’s one that should be explained in a positive way to consumers. Part of the allure of these gemstones aside from their beauty after treatment, is the story of their exotic discovery. Adding details about this ancient heat treatment to maximize the stone’s allure is part of its mysterious voyage. That can become a key aspect in your presentation in educating your customers on the backstory of their purchase. So arm them with the fascinating knowledge of this stone’s passage from mine to their jewel box.