Secondary tube channels in Madagascar sapphires before and after heating. Image by E. Billie Hughes

Here we have a close-up of a “fingerprint” inclusion in a Madagascar sapphire, shown before-and-after heat treatment. In this paired photomicrograph series by E. Billie Hughes, you can see exactly the kind of detail gemologists rely on when assessing evidence of treatment.

Before and after heated to 1500°C

Secondary tube channels in Madagascar sapphires before and after heating
Above: Partially healed fissure, or “fingerprint,” in sample 3 before heating. Note the elongated, tube-like channels. 

Photos using diffuse transmitted light. Photomicrographs by E. Billie Hughes; field of view 1 mm.
Above: After heating the stone to 1500°C, many of the jagged edges of the tubes have become rounded,
and some even “neck down” to form smaller, rounded shapes in place of elongated tubes (Hughes, 2017).

These before-and-after shots are remarkable — not only for what they reveal gemologically, but for the precision of the presentation seen here. To have two images line up this perfectly, allowing you to pinpoint every shift and subtle change, is truly extraordinary.

We spoke with Billie, who explained just how demanding this kind of work can be.

“It does take an extraordinary amount of time and patience to get these before-and-after shots as close to each other as possible,” says Hughes. “I can share a few pieces of advice.

  • Take more ‘before’ shots than you think you’ll need, because it’s hard to predict what will change after heating.
  • Keep notes on lighting conditions, so you can try to keep it as consistent as possible between rounds. But it won’t always be exactly consistent, because the inclusions change and you may need to make adjustments after heat.
  • Leave a little room for yourself to crop things later as needed.

“It can already take real focus to get one good inclusion photo, but doing these before-and-after series is definitely more challenging! Especially in some cases with what we’re doing where we may end up with four or five shots in a series.”

NOTE: Hughes notes that while the article below talks about low-temperature heat treatment, the images above are of a sapphire after heated to 1500°C – considered “high” heat.

Madagascar has become one of the world’s top sources of fine blue sapphire in recent times. In addition to beautiful untreated material, increasing numbers of treated stones have appeared in the market. Some have been heated to relatively low temperatures, below 1350°C, to lighten their color. To help separate unheated and heated Madagascar sapphire, the authors performed experiments to document the changes they undergo with low-temperature heat treatment in air, which is an oxidizing atmosphere.

Tap the image above for the full article on Madagascar Sapphire – Low-Temperature Heat Treatment Experiments
Roskin Gem News Report