HT-P (High temperature Pressure) sapphires were started for treatment in 2009. This treatment is not an easy treatment to do, according to our research, its a treatment that is very similar to the standard Heat treatment that is available readily in the market – and since the difference is little (Especially with Microscope the traits were similar to those of traditional heat (Lotus Gemology, 2019). Interesting that this sapphire treatment that is capable of doing permanent deformation of the sapphire lattice, in particular crystallographic orientation, not maybe in the entire direction. So you know some people might say, we are using a kind of press which pushes sapphires from all directions. Ceramics in general, including sapphires are resistant to compression, but they are not resistant to tension. This is a property of all material with covalent or ionic bonding. But if you pull it, it would break apart quite easily or show deformation. In terms of sapphires its not so important – even though you apply compression from all sides, you will still have tension components at particular crystallographic direction, because its an anisotropic material.

The below question and answers are taken from our webinar together (with some additional comments from Navneet Gems): Mansoor, M., Agarwal N., Navneet Gems (2020). Heat Treatment of Blue Sapphire (The potential effects of pressure) [Video].

  1. Role of inclusions in the HPHT process of sapphires – can you explain that in comparison to the conventional heat treatment that we see in the market today?

(translated to simplified version by Navneet Gems)

You say, this is very difficult to answer. When you have inclusions, doesn’t matter if its traditionally heat treated or this new HPHT sapphire – its always more difficult to heat treat included stones at these temperatures. With this process, the addition of pressure; can be good or bad – difficult to say. But overall, it may not be that good to apply pressure to included material. To back this hypothesis we also have here some images from GIT which can be helpful to say that this treatment can produce varying results and isn’t easy to control.

Before and After HPHT sapphire
Image Courtesy: GIT

2. Why is this HPHT treatment mostly carried out with ceylon sapphires – something to do with the types of inclusions in these srilankan stones?

(translated to simplified version by Navneet Gems)

I strongly believe that this treatment is alot more effective on srilankan stones. The reason goes beyond its inclusions – it also has the do with the trace elements (chemistry). If you already have a material too dark, (Example: Australia Sapphire,  Diego) – you would get a significant solubility of titanium in it – meaning you would get darker sapphires which is not that pleasant. On the contrary,  Srilankan stones have, the perfect trace element chemistry to show good result. I also believe Metamorphic material may be better suitable, if the processes & technology are similar what they have mentioned by the GIT.

3.  HPHT has already been in the market since 2009 – the market tends to accept such things because of the high market penetration… our industry is a laid back industry. Like Mr Richard Hues has mentioned for example when traditional heat came out, it was years later they discovered it – so it was grandfathered as “Traditional” and on another hand we had the beryllium diffusion. The beryllium treatment was soon identified by gemologists – and now we see the trade is very critical about this treatment – do you think, Mubashir, this is why the HPHT is an accepted treatment in today’s world?

I think you are right – not completely. Sure, there are aspects to your thesis that I do agree with. This process itself is very complicated compared to the traditional heat treatment. The simplicity of the beryllium treatment – made it hugely available in the market and of course cause alarm. There is a very interesting webinar video between Justin K Prim & Vincent Pardieu (Field gemologist with passion for gems, people and conservation) – that they had with Mr Terry Coldham.

They were mentioning about the beginning of the beryllium treatment – as long as they were not doing this beryllium on the pink sapphires from Ilakaka, changing to the padparadscha’s – the industry was fine with it. But as we started seeing a-lot of the beryllium in large quantities without any control – we started to see things completely change the industry became critical about it. The fact that this process of HPHT sapphire is very complicated makes it very difficult for this material to penetrate the market that easily, unless something very significant changes in the treatment itself or the way they are doing it. I dont know what the technology is behind this. I just explained the physics behind the HPHT treatment – what would happen if you applied pressure at these high temperatures – if you are able to get permanent deformation, its only about time that this treatment can go to the next level. That will be critical. This will make the consumers worry, but I strongly worry the Gem labs should be very cautious about this treatment and keep in touch with the way the process if progressing.

I would like to add here about the experiment we had back in 2016. In one of the experiments, we needed some material to insulate two electrical conductive layers from one another so in between we needed an electrical insulator. The process was taking place in about 2200 degree Celsius but at that point of contact the temperature was around 1800-ish degrees Celsius. Now if those two layers would touch each other we would have a problem and the experiment would be ruined. So we wanted to put something to act as a bier so they dont touch each other. At that point, while I was looking around, I couldn’t find something that would suit the experiment, so we decided to synthetic sapphire that I had in hand as that would stand 1800 degrees easily. So I had placed it in there, the part on top of the sapphire had some weight, after the experiment, (the experiment was really long >10 hours) we opened the furnace. The results of the experiment that with my unaided eye I could see permanent deformation. Thats the reason I say, keep an eye.

4. What is the future of the HPHT treatment?

See it would depend on the market. I have no problems in this treatment, when the Koreans started, this was initially really shocked because in order to keep the sapphires stable under those conditions its really challenging, we put our hats off. So as long as there is proper disclosure in the market, it would be much better then the flux level treatment as this is next level. As long as people are efficiently disclosing it and the market should be aware – this market should not be sold as traditional treatment. If technology improves, there is more influx of such HPHT sapphire goods, that will not be very good in terms of the market sentiment. Initially when the beryllium treatment on sapphires came out – yes it was a brilliant treatment but later it just got in high supply hands. It’s bad reputation became a ruin for all strategy because of non disclosure from the people.

5. At the moment it seems only a few labs are giving a call on certificates for HPHT sapphires – why is it so difficult?

Very good point. Gemology is based on statistical information, unfortunately. So a great deal of what statistical samples of heat treatments to the gem labs – how can we study, analyse – the problem with that it makes it very difficult – if there is a slight difference in treatment technology or method. I am not the best person to ask – maybe one of the Gem labs can answer this question very well.

6. Why is HPHT the right or wrong term? Should we call them HTP or HPHT, or just call these basic heat from your point view because there isn’t a general consensus in this regard yet!

I have been reading geological articles from different labs – I strongly agree with the Swiss Lab – that this material is HPHT. However many people in the industry are comparing it with HPHT in the diamond business which actually the process is much higher in pressure which are like 5 giga pascals, compare to around 100 mega pascals of this HPHT sapphire treatment and therefore we should not call it HPHT. For sapphires if you are able to get permanent (plastic) deformation – so where it the line? That is something for the industry experts to decide on…from what I can say this material has all the possibility of calling it the HPHT sapphire because the pressures for the stone sapphire itself are pretty high.

6) Is the FTIR spectrum the best way to detect HPHT blue sapphires?

Yes and No.  Yes if the kind of techniques that are being used today – continues- then yes for today this is useful BUT the problem is if you use a slightly different setup of the heat treatment process. The peak that people are talking about has nothing to do with the pressure. The entire world of gemology has this beautiful part to it – we dont rely on any single test. We bring about the series of steps. We believe that the ghost fissures would constantly stay on – as its very difficult to remove that. This makes us understand that we should use the FTIR spectrum and the microscope (which is a very close friend of a gemologist).

Microscope is a gemologists’ best friend – Lea Danielle (Carlsbad Campus, GIA)

7) So, You mentioned dis-locations increase in the sapphire. Can we see those dislocations under a microscope and use that as an evidence of HPHT?

No, unfortunately we cannot. Dislocations are atomic level displacements. We can’t use an optical microscope and have a look. These are destructive methods of seeing the microscope. However there are some recent advances in the field of microscopy. Some researchers are developing next technology that will give us create a 3D map – I think in Princeton, Published in the journal nature. (https://phy.princeton.edu/sites/physics/files/bhamre_thesis.pdf) People should still consider that gemologists best friend is the microscope. Maybe going to the next level would be interesting.

8) Many of our listeners today are curious to understand the durability of the HPHT sapphires. Lotus Gemology has conducted some very nice experiments on testing the durability of HPHT sapphires compared to traditional heated blue sapphires- and have concluded that the durability problems of HT+P treated sapphires could not be substantiated by tests, which were carried out by several laboratories. What are your thoughts? 

So we saw two papers in this regard. We saw the claims of Dr Prettyi – GRS – she claims this will cause some problems in durability issues, where as Lotus Gemology says not the same. I think they are both right. You may have seen the old movies where the Ironsmiths are working hardening the material of the swords. The yield strength of these sapphires increase – the deformation becomes difficult. “Usually” the increase of yield strength, the fracture toughness would decrease. With sapphire its behaviour is different, the behaviour is brittle – if you have applied plastic deformation – it could lead to decrease toughness – so in this aspect Dr Peretti could be right. We would like to test the mechanical durability on a synthetic sapphire, I would never do this on a natural sapphire, because of numerous types of factors.

Further Q&A will be uploaded here soon. Kindly see the video for complete answers and research.

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Istanbul & Bangkok have come together to talk about HPHT Treatment Of Blue Sapphires. (Heat treatment of blue sapphires and potential effects of pressure). This webinar was for a Q&A webinar on Zoom with Mubashir Mansoor on Friday – May 22th 2020.  For Citation: Mansoor, M., Agarwal N., Navneet Gems (2020). Heat Treatment of Blue Sapphire (The potential effects of pressure) [Video]

Navneet Agarwal (@navneetgemscom) GG GIA (USA) & Marketing Manager at Navneet Gems & Minerals. Mubashir Mansoor (@materials_scientist) Gemologist, Researcher in Materials Science and Physics. (Ultra High Temperatures Specialist)

This video is strict protected property of Navneet Gems & Mubashir Mansoor, but with correct citation and reference it can be used in research papers, or elsewhere.

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OUR WEBINAR CONDUCTED (WRITTEN FORM)

We would like to welcome everyone on Zoom. This is Navneet Agrawal and I am glad to start today’s webinar which will be about the hot topic of HPHT, or pressure assisted High temperature treatment of Blue Sapphires. So, So, So, I can see that we have a full house and people joining from all across the globe, thank you so much for coming and joining us today. We will be publish this video on NGM’s youtube channel and across our social networks, so if its too late or something – you can always come back and catch up with this webinar later.

For those who are with us….Our speaker on this topic is, Mr. Mubashir Mansoor – he is an upcoming gemologist & a researcher in material science and physics, with special focus on ultrahigh temperature sintering processes. He will be joining us all the way from Istanbul, Turkey.

We will begin with a comprehensive presentation by our guest on the basics of heat-treatment of blue sapphire and the effects of pressure on this process followed by a question and answer session on the topic, later. Mubashir has a tendency of getting very deep into the scientific background of the subjects so feel free to write ANY questions you may have in the Q&A box.

So without further adue, the floor is yours Mubashir. Lets begin.

Watch our full video here on HPHT sapphires with Mubashir Mansoor.