Date: 01/03/2021; Subject: glass sold as topaz, similar R.I. 1.62 (but no birefringence) & SG 3.55

Imitation of natural gemstones with glass is common but it is very rare that both refractive index and specific gravity match the natural stone. The two gems in question had "Swiss blue" color but appeared a bit dull compared to natural topazes, so someone used to work with topazes may detect that something is stange. It was also more scratched than usually topazes are - which can be an indication of lower hardness. Although R.I. was 1.62. it lacked birefingence so only by refractometer testing it is possible to tell the "gems" where single refractive (topaz is double refractive). SR was confirmed with polariscope but the two pieces did not displayed the "snakeband" usual with glass - another rare thing. Finally, microscope

Date: 15/10/2020; Subject: Irradiation treatment for yellow sapphires.

Since mid 2020, several gem traders have had the bad surprise of buying unheated golden yellow sapphires and the stone color to progressively fade to a light and pale yellow. These stones were not heated but treated by irradiation, a treatment which is difficult to detect by any method other than keeping the stone for examination during a long period of time and simply looking if the color fades away. In the case of the stones illustrated here below, it took two months for the color to fade from left picture to right picture.

Although this treatment is now new, it was not common in unheated stones. However, as it becomes more common now, in order to make customers aware of such risk, starting from this date, GFCO GEM LAB is to mention the following comment on the left page of the report under Testing Methods & Equipment Used: "Not tested for irradiation and possible impact on color stability". This comment is to feature for all yellow sapphires of intense yellow color which the laboratory has not kept for examination during a period of 30 days in order to witness if the stone color fades away. Please consider this warning valid for all GFCO GEM LAB reports issued prior to 15/10/2020 where such comment does not feature.

Date: 01/03/2020; Subject: Bangkok office moved to Mahesak from JTC

In March, GFCO GEM LAB moved to J.K. Building, Mahesak Soi 3, third floor, room 302. We hope to see you there soon.

Date: 01/09/2019; Subject: Warning! Glass sold as tsavorite

Over the last few weeks, we have had several lots of tsavorites which were mixed with glass. The color of the glass perfectly matches the vivid green tsavorite color.

Date: 01/05/2019; Subject: precious metals testing in jewelry reports

GFCO GEM LAB now checks the purity of precious metals in its "limited jewelry report" using X-rays on a 10 microns depth. Mounted diamonds are tested using microscope observation and fluorescence. Nonetheless, the focus remains on coloured stones.

Date: 01/02/2019; Subject: Assembled stones sold as natural unheated stone, then labelled as glass-filled by some gemological laboratory

This week, we have seen something new. A client gave for certification a blue sapphire he purchased as natural unheated stone. Under microscope, the gem effectively had shiny silk, unbroken needles and others various undamaged inclusions - defintely sapphire inclusions. However, one side of the gem was clean. RI came normal on the crown but SG came close to 4.20, which was too high. Then the obvious came when looking at the gem under polariscope, the sapphire area was blinking while the lead glass area was showing "snakeband" effects; the limit between the natural part and the assembled part of the stone could be seen clearly. What is interesting is that the stone had been certified as glass-filled by a lab with advanced equipment because they had detected lead glass, but this was not a glass-filled stone but an assembled stone between part of an unheated stone and a piece of blue lead glass. By microscope observation, the limit between the natural part and the lead glass part was very difficult to see.

Date: 01/03/2018; Subject: bubble-like inclusions in a stone - can it be natural?

Every gemologist knows that seing bubbles in a gem is never a good sign, it is usually a clear indication that the gem is synthetic, glass or plastic. However, beryllium treatment also results in the creation of bubbles in gemstones. Beryllium is a gaz and such treatment requires high temperature. From an examination point of view with microscope magnification, this treatment in rubies and yellow sapphires transforms natural inclusions in what seems to be bubbles. However, these last ones are different than the bubbles found in synthetic stones because at the center of the bubble stands the remains of the original inclusion which can be seen using high magnification. Furthermore, beryllium can create bubbles near the surface of the stone which can easily be mistaken with the bubbles of synthetics. Finally, bubbles in synthetic stones are usually not arranged in a fingerprint pattern except for some flux rubies which appearance can be very close to natural rubies of Burma heated at high temperature. It is often not an easy task to separate relatively clean rubies and yellow sapphires treated with beryllium from synthetic stones but again with the experience and focus on checking if the bubble is a bubble only or the remain of a natural inclusion, it is possible to do so by microscope examination. We are confident on our testing results as we have submitted such stones for double checks to renowned laboratories which have also proceed to chemical testing and confirmed the natural origin of the stones.

Date: 01/06/2017; Subject: Welcome to our Bangkok office in JTC

We are pleased to announce that our office is now in the Jewelry Trade Center, Silom road, room 341B/C. We look forward to serve you.