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PostPosted: Sat May 05, 2007 10:01 pm 
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Lee Little has a great post here that I can't find. He describes diffused stars.

Can it be this one Steve?
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For the star, if it looks imperfect or faint at all, it is probably natural. Experience will help you the most, look at lots of them. The diffused, at least as far as I know, are pretty obvious. Strong clear white star with exceptionally crisp edges, appears to float on the very surface, does not penetrate at all. Shows up in the faintest light. The legs CAN have crooks in them, not absolutely straight.

Here is the link:
http://gemologyonline.com/Forum/phpBB2/ ... ght=#24898


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PostPosted: Sun May 06, 2007 6:56 pm 
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JB wrote:
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The description of the stone using "possible" heat treatment may just be a general disclaimer when the original chain of ownership from mine to dealer is unknown.


Steve wrote:
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with all the treatments going on I feel more comfortable saying possible heat. if i don't know.


Finally, after about 25 posts we get an answer to one of the original questions. The rest was answered with Vincent's post regarding the chemistry. Didn't want to go there in the Beginners Forum but, there aren't easy answers for every question.

This thread is a good example of how simple questions lead to more complicated answers.
Bottom line (if anybody has been following) don't expect to see a lot of heat treated natural star corundum out there. If there's enough titanium in the "original brew" mother nature will do the work ( that's why they add tianium oxide in the heating treatments to diffuse a star). If not, you heat to eliminate or minimize the silk inclusions.
Heating of natural star corundum will probably have minimal effect on the overall quality of the star beyond what the earthly process has already created. It's got the right ingredients to make a good cake or it doesn't. Rebaking doesn't make a cake out of something that lacks the necessary ingredients, unless it never fully cooked (and cooled properly) to start with.
Might help the color a little but, it reaches a limit where the asterism is sacrificed for color.
That's my 2+2.


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PostPosted: Mon May 07, 2007 9:16 pm 
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jb. sorry it took so long to answer your question about how I handle the disclaimer. I must have been tired and didn't see your post. It's just that dealers will say, "not heat treated" for instance if it's most likely to be true. Influenced by the fact that it sounds better. Then there are the guys who just lie, in all types of business. I'd love to say unheated / untreated too but my mom would get mad at me. That's worse.

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If you heat a star ruby or a star sapphire at 1600 degrees with a slow cooling, I'm positive it will be possible in most cases to detect the treatment...


That's what I would think. Just look at the altered inclusions. I'm no gemologist so I only know what we go by in the trade. I appreciate the input from the graduate gemologist here.

Thanks for the Lee Little link. That's the one.

steve


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PostPosted: Thu Jun 05, 2008 6:47 pm 
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The following example complete with AGTA report fits the topic so well, I felt the thread could get a bump on the account old as it is.

Here goes, heated pink sapphire star along with reports saying 'heated' and the seller's explanation of what must have happened to the stone: LINK to source

Pretty much the clincher here:

Image

Image Image

For the record, the story along with the listing goes in line with what was written earlier on here:

"This star was heat treated before cabbing to approximately 1,000 C (1,850 F). This treatment removes a characteristic bluish color from the stone. This does not cause the red color to get darker, but when purplish star rubies are heated they often become a more pure red. However, when temperatures exceed 1,300 C (2,370 F), the silk inclusions that cause the star are altered, causing the star to disappear, so as you can understand heat treating a natural star sapphire is an art form itself. "


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 Post subject: Re: heated star sapphire and rubies?
PostPosted: Sat Nov 23, 2019 6:26 am 
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This is a very interesting thread. I just posted elsewhere asking a few questions about fluorescence in star cabs.
In another thread:
Star Ruby pricing
viewtopic.php?f=6&t=12713&start=15
vincent pardieu wrote:
Hi Barbra,
Star sapphires/rubies are commonly heated with blow pipe in Sri Lanka (for centuries I guess) in order (typically) to make the stone less purplish as such "low temperature" technique does not reach the point where the rutile needles, responsible for the star, will be affected.
For few years you can also find many in the market many star rubies that have been heat treated using lead glass additives. As here again the treatment is performed usually under 1000 degrees, it does not affect the star. Most of these stones are heavily fractured rubies from Madagascar/India. Filling the surface reaching fissures with lead rich glass is usually done on the rough as filling fissures with lead glass enables the stone to be less likely broken during the cutting process. It also improves the stone transparency and general aspect.
Nevertheless as with most filled stones durability is a concern as the filler can get damaged particularly during jewelry making process particularly if the jeweler is not aware of the treatment. If the treatment was done correctly the filled fissures will be invisible for people not aware of such treatment and with a minimum of gemological training.

You can get more details on the following study:
http://www.giathai.net/pdf/Lead_Glass_Filled_Star_Rubies_20100201.pdf

All the best,


Mr. Padieu , if you are active here, the link up above you posted is very interesting. Am researching my own question I put in that other thread about fluorescence in Star Rubies being one possible indicator yay/nay over treated stars/lead glass fill. At least when it comes to the "Madagascar" stones info in the pdf article, it just might? And why would Sri Lankans use the low heat method to "(typically) to make the stone less purplish"? Yes, I'm the nitwit newbie here, but isn't purple also a lovely color? They want to make them more "ruby" colored?

"Introduction: Meeting the Thai burner.
In January 2010 the GIA Laboratory Bangkok was contacted by Mr. Mahithon Thongdeesuk( ), from “Jewel enhancement by Mahiton Co. Ltd” in Bangkok, a Thai burner involved in the development of the lead glass
treatment since 2002. He informed the authors that he had finished developing a new product which he will soon release in the Thai market:
“Lead glass filled star rubies”...

...UV Fluorescence
The 34 lead glass filled star rubies (Figure 1) were observed under both short wave and long wave ultra violet light using a UVP, UVLS‐28 EL series, 8 watt, UV lamp with both 365 and 254nm radiation. Their reactions (Table 1) were found to be more subdued (italics mine) when compared to the strong reaction commonly found in iron poor rubies like those from Burma and quite similar to other iron rich rubies from East Africa and Thailand/Cambodia.
Table 1:
SWUV (253nm) Inert (dark red stones) to weak red to orangy‐red (bright red stones)
LWUV (365nm) Weak to moderate (dark red stones) to strong red to orangy‐red (bright red stones)
...The quantitative data obtained provides some insight into their source type and helps with regards to their origin determination. Their chemistry is characterized by relatively high levels of iron compared to known star rubies from traditional marble type deposits like Mogok (Burma) and Vietnam meaning that these rubies host rock is probably not marble. Thus chemistry seems to be a reliable method to separate these lead glass filled star rubies of reportedly Madagascar origin from star rubies from these traditional Asian deposits..."
Attachment:
lead glass fill Madagascar vs untreated Burma Vietnam png.png
lead glass fill Madagascar vs untreated Burma Vietnam png.png [ 174.11 KiB | Viewed 263 times ]


Does anyone know if these stones have hit the market? Surely by now...

"...As to the best of our knowledge, the product isn’t currently available in the market despite some existing reports on other lead glass filled rubies looking quite similar (GAAJ, 2004, Hainschwang, 2009, Pardieu, 2006), this preliminary study cannot provide information regarding the availability of this new material. Nevertheless it seems that soon large quantities of this material might be available in Thailand.
The reported Madagascar origin of these stones could not be confirmed. Nevertheless the gemological data collected on these stones is very similar to that known for stones from some ruby deposits in East Africa. A visit to the deposit in Madagascar would be necessary to confirm their origin..."

Is microscopic inspection combined with that spammer spectrometry (and fluorescence?) now the only recourse/telltale origin sign to professionals - combined with any known glass-fill use in those countries - that gives away these lead glass filled stars? It seemed that the inspections with 10x loupe were not so easy for the pros in the pdf writeup, very hard to detect. What happened to this company? Some "unheated" stars sell for double digit thousands! Oh my, I had no idea the lead fill extended to stars. silly me...if Sri Lankans have been heating for centuries with a blow pipe (at least it sounds romantic) I suppose I can live with that, but lead glass fill? woe, woe is me... :cry:


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 Post subject: Re: heated star sapphire and rubies?
PostPosted: Mon Nov 25, 2019 4:10 pm 
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tinkie wrote:
Mr. Padieu , if you are active here, the link up above you posted is very interesting. Am researching my own question I put in that other thread about fluorescence in Star Rubies being one possible indicator yay/nay over treated stars/lead glass fill.

Not in my experience, no. The lead glass doesn't fluoresce red like the ruby will but that's not easy to see in the hand. These rubies in general do tend to be more iron-rich and less fluorescent, but they'll still light up.

tinkie wrote:
isn't purple also a lovely color? They want to make them more "ruby" colored?

Purple absolutely is lovely, but it isn't as highly valued as pure red or pink. If it's any comfort, most of the time they're driving off a pretty slight purple off-color, rather than starting with a magnificent purple and ruining it. Pure colors are typically more highly valued, and just a hint of purple isn't always that great


tinkie wrote:
Does anyone know if these stones have hit the market? Surely by now...

Yes, I was sold some a few years back. When I got the stones in I thought they looked way too nice for the price I'd paid, and after finding the above article I was able to locate bubbles with my microscope. They are not as easy to spot as in faceted stones, though! These stones are pretreated with hydrofluoric acid to dissolve out any silicate inclusions, and these tend to run flat and perpendicular to the C axis. As such the glass is distributed in thin layers, so you typically have to view the stone from the side, and the bubbles are a lot subtler than they often are in faceted stones.
In some ways the treatment is better than the typical garbage, firstly because the resulting stone looks better, and second because the star ensures they can't stick multiple bits of ruby together into one piece. There were some preliminary reports that they seemed to be more stable too, though I am not sure about that. Still, lead glass just isn't sufficiently stable and I wouldn't intentionally buy or sell these. So far careful microscopic examination has been sufficient but it's more challenging than usual.

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 Post subject: Re: heated star sapphire and rubies?
PostPosted: Tue Nov 26, 2019 1:40 am 
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tinkie wrote:
fluorescence in Star Rubies being one possible indicator yay/nay over treated stars/lead glass fill.

Stephen Challener wrote:
Not in my experience, no. The lead glass doesn't fluoresce red like the ruby will but that's not easy to see in the hand. These rubies in general do tend to be more iron-rich and less fluorescent, but they'll still light up.

Hmmm, I'm reading this over and have confused myself...so you're saying lead glass in transparent natural (but ff rubies) AND natural but lead glass treated star rubies don't fluoresce like a natural ruby - or in the context per the quote from the GIA video on the top 4 synthetic grown/fake transparent rubies? I'm trying to digest the quote from the GIA lecturer on "transparent" non-star rubies and staying away from anything that glows extremely high in long uv and has a very good reaction in short uv = quote, as "most probably synthetic." and what you've written.
Are you talking solely about "lead glass" as in all-glass rubies/fakes/treated synthetics with additives to make them "glow"? Sorry, long day here haha! So what would it mean when my huge gray purple honker star (but not a visually gorgeous desirable top gem) lights up with a nice solid even pinkish red glow under uv? I'm so sorry, am in the middle of a brain phart lol.
I guess when I get your microscope I can go hunting for glass bubbles :D , but I don't think any of mine are glass filled. I need to prove myself wrong and find out. I guess part of my fascination is how something honestly so ugly closeup can look so nice just an arm's distance away lol.

Stephen Challener wrote:
Purple absolutely is lovely, but it isn't as highly valued as pure red or pink. If it's any comfort, most of the time they're driving off a pretty slight purple off-color, rather than starting with a magnificent purple and ruining it. Pure colors are typically more highly valued, and just a hint of purple isn't always that great


All of my stars are purple, some more grayish, some a nice medium rich lilac, but they have wonderful growth patterns and some have reddish seams with reddish/pinkish areas along the sides if you look closely, more transparency, colored golden brown dot inclusions magnified here and there. Am I safe to believe if it has started out as a krappy grayish purple stone, they have no where to go with it to drive it to pinkish? Hence better chance being no glass fill? So a truly natural star ruby - though in an undesirable color - will fluoresce much better than a lead glass filled natural as long as it has low iron content? Brain salad at this point lol! Maybe the quick method is to pour acid on them and see what happens! :lol:

Stephen Challener wrote:
Yes, I was sold some a few years back. When I got the stones in I thought they looked way too nice for the price I'd paid, and after finding the above article I was able to locate bubbles with my microscope. They are not as easy to spot as in faceted stones, though! These stones are pretreated with hydrofluoric acid to dissolve out any silicate inclusions, and these tend to run flat and perpendicular to the C axis. As such the glass is distributed in thin layers, so you typically have to view the stone from the side, and the bubbles are a lot subtler than they often are in faceted stones.
In some ways the treatment is better than the typical garbage, firstly because the resulting stone looks better, and second because the star ensures they can't stick multiple bits of ruby together into one piece. There were some preliminary reports that they seemed to be more stable too, though I am not sure about that. Still, lead glass just isn't sufficiently stable and I wouldn't intentionally buy or sell these. So far careful microscopic examination has been sufficient but it's more challenging than usual.

Hmmmm, okay, if you don't mind, once I get a microscope I might be pestering you on this. When you're viewing this "flat and perpendicular" layer, what magnification are you using? I find this fascinating. First I will have to know what natural star ruby looks like from the side to compare. Does anyone sell comparison kits of gemstones that are known naturals? What would that search name be? Apologies for sounding so dense on this, truly.


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