Hi everyone, recently joined the forum hoping to learn more about gemstones. All replies and feedback will be appreciated:)
Having been researching for vivid yellow sapphire lately, I found there’s a particular “kowangu” type heated yellow sapphire variety from Sri Lanka which can reach an extremely high saturation. Such variety is said to be able to stay lit even under low and dim lights, while persistently performing well across various lighting conditions, is this an accurate description in terms of its performance and colour behaviour? If it’s correctly said, is heating kowangu rough the only way to achieve that saturation level, or can untreated stones reach that colour intensity?
Thanks in advance~
Hi everyone, recently joined the forum hoping to learn more about gems, replies and feedback are all appreciated:)
I’ve been researching for vivid yellow sapphires lately and found the true Ly strongly saturated ones are usually associated with the “kowangu” sapphires or rough in Sri Lanka while most we normally found say on the internet are more pale in colour.
My questions are: -The strong yellow kowangu type sapphires are said to be able to stay lit even in low or dim light compared to sapphires of other colours which often gone dark in such lighting. Is such performance difference truely descripted. - within yellow sapphires, Is heating kowangu rough the only way to achieve the mentioned colour intensity? Can untreated stones reach that level? - How rare is such strong yellow sapphires?
Joined: Fri Jun 25, 2010 12:04 am Posts: 257 Location: Idaho
Interesting - Google the term "Kowangu Pushparaga" and you find that it is a (local Sri Lankan?) term for one of several types of geuda sapphire from Sri Lanka. That particular type is known for heating under oxidizing conditions to a yellow color.
Yellows in sapphire can be weirdly finnickey. Some fade, particularly unheated ones (though some of them I guess can be restored with UV exposure??) while heated stones are totally stable from what I understand. I assume the unstable or tenebrescent yellow color is related to the unstable colors that can be induced in sapphire by artificial irradiation, but the exact relationship I am unsure of.
Precisely speaking it’s true I got the said info from a vendor based in Sri Lanka. I understand the concern to be conjured by vendor especially when dealing with a close to source one that you have never dealt with, thanks for such remind. However, I found the conversation with them quite transparent and honest after starting communicating. I’ve never been pushed for any purchase, my original enquiry was not for yellow sapphire, and I have even not committed for any stone in deed, and was shown a great willingness to just talk about different things about different gems.
With the mentioned yellow sapphire topic being one of the aspects that caught my attention and curiosity more, I do wish to gain more views and understanding on that.
Interesting - Google the term "Kowangu Pushparaga" and you find that it is a (local Sri Lankan?) term for one of several types of geuda sapphire from Sri Lanka. That particular type is known for heating under oxidizing conditions to a yellow color.
Lotus Gemology (Richard Hughes & Co.) might have something on the subject, or maybe a good dig thru the GIA site...
Yes “Geuda” is a term that is more talked about or better documented. What my vendor also shared with me was kowangu is traditionally blowpipe low heated, which by no means is any sort of heavily or unacceptably treated stone.
As for my description of the potential performance of kowangu yellow sapphire, apologies if I made it sounds exaggerated. More technically speaking, I believe the vendor was just solely trying to express the saturation intensity is hard to surpassed by untreated ones. Or I may revise my question in such way, while many untreated yellow sapphires are relatively lowly saturated, what is the roof of its colour intensity despite its rarity? Can untreated ones be truly vivid? Appreciated of example or pics shared:)
Joined: Tue Apr 05, 2016 7:58 pm Posts: 1424 Location: San Marcos, CA
I will have to stick with beliefs that it is just a lot of puffing by your blowpipe. If it were as your vendor is blowing smoke about, do you not think that any one of the world renowned gemological authorities would have if front and center. All I found as well was just what has already been stated, just "gouda" corundum heated to achieve a yellow. Whether it be a vivid yellow or holds some magic phenomenon is not commonly found or it would be a topic of wide controversy to understand. I do not find any images of this gouda to be a vivid yellow. Please post some of your vendors images.
I will have to stick with beliefs that it is just a lot of puffing by your blowpipe. If it were as your vendor is blowing smoke about, do you not think that any one of the world renowned gemological authorities would have if front and center. All I found as well was just what has already been stated, just "gouda" corundum heated to achieve a yellow. Whether it be a vivid yellow or holds some magic phenomenon is not commonly found or it would be a topic of wide controversy to understand. I do not find any images of this gouda to be a vivid yellow. Please post some of your vendors images.
I actually understand your logic. To be honest I have no idea why it’s rarely talked about or there’s a lack of info even from the big authorities. May be due to yellow has not been as desired as other mainstream colours? Or could it be even the heated vivid yellow is still exceedingly rare that it simply can’t create a market? I don’t know, really. Sometimes even rarity, beauty are in place, lack of or low demand would still adversely impact the intention to promote or even talk about it. Just my guess anyway.
Below are some of the stones from the vendor.
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Joined: Tue Apr 05, 2016 7:58 pm Posts: 1424 Location: San Marcos, CA
In my reading of these articles, it is has already been established with extensive testing of many yellow sapphires. In this case puffing or just an excited color gemstone conversation between gem lovers of yellow sapphire. I took note especially in the Market Trends article of two sentences and looking at the Op's images. "Any hue of yellow will be compromised for quality once there is a brown modifier which is seen more than often." And. "Of course, the safest practice is always to use advance testing techniques to establish the origin of color, especially in larger stones.
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