Hodgkinson method to determine filled ruby...

[soberguy]

Ok... I have done this on every ruby I have (around 50), and in every store I've been in for the last year'sh. Hold the ruby up to a bright light (I think incandescent works best). You should see distinctly red/pink/blue in the refracted light passing through the stone. Please note I am NOT a gemologist or geologist, so my terms may be mistaken lol! If you see red/orange (in my experience after 100's and 100's of dollars in tests...), you have a "lead glass" filled ruby. This will NOT determine natural origin! Synthetic rubies react the same. Just an interesting thing I noticed after seeing some "fine" rubies in a certain store of GREAT repute that has been discussed on this very forum. Just because something has been certified natural does NOT mean it hasn't undergone extensive treatment... Even in high end stores. BE CAREFUL! It's a wretched jungle out there for colored stone fiends! Read the fine print regarding treatments allowed.

This test also will not determine traditional heating, as I have several heated/unheated examples that react the same to this test, red/pink/blue. Not a single one of my rubies that is natural and NON filled show anything but those colors. All of the rubies that tested filled with a foreign substance do NOT show red/pink/blue, but red/orange.

Just an interesting thing! Hope you are all well!

 

[LD]

This is very interesting because I was always led to believe that if you see a blue flash it MAY be indicative of filling. I wonder if anybody else has thoughts on the subject?

This talks about blue flash also - see bottom of page 26

http://lgdl.gia.edu/pdfs/gemsandgemology/articles/Sp06-G&G-article-on-lead-glass%E2%80%93filled-rubies.pdf

 

[soberguy]

I think that is true if you're seeing it as a sort of wispy haze in the stone. I'm talking about something different. When the light goes through the stone, and you see the color of the refracted light. In the traditionally heated/unheated NON filled certified rubies I have that is what I see. In the stones that have come back filled I do not see those colors, but red/orange/yellow.
I know exactly what you're talking about, and I see the exact result pictured in my "filled" rubies. Just thought this was a kind of quick test before buying something . I saw a ruby in a certain high end store that looked filled, thus the research. I have sent so many stones out for testing it's scary . Gratefully, the prettier ones were natural, and several unheated/untreated. But a LOT were filled. I was just looking for some way to tell them apart.

 

[LD]

No soberguy I'm not talking about a haze. I'm talking about blue flashes.

I really think it's very dangerous for anybody to identify filling or not based on colours seen. It really takes a lot of experience to ID fillings. Seeing a blue or orange flash is really on an indication of something but not actual evidence. It's a warning sign.

 

[soberguy]

I am not talking about flashes, I am talking about refracted light. I saw the exact picture you linked to. That is not what I'm talking about. I also do not think I was suggesting this was a sure test of any kind, more of an interesting observation... This is what I'm talking about:

 

[Pandora II]

With regard to lead-glass filling, the easiest way to look for this is with a x10 loupe and a light source. Using reflected light you look for differences in lustre and polish that are due to the lower RI and softer nature of lead-glass. They are pretty easy to spot if you are looking for them and know what to look for (silica glass is easier to spot than lead-glass). They also tend to show gas bubbles and the flash effect - mainly blue but sometimes orange. If areas of filler are large then it can look pink or yellowish.

(You could also always stick them in a bit of lemon juice as that doesn't agree with them at all - household cleaners are extremely aggressive to them!)

I've always know the Hodgkinson method as one for distinguishing ruby from other red gemstones by using spectral images - I've never seen it promoted as a test for filled rubies (do you have a link?) In any case, it is a 'confirmative' not a 'diagnostic' test and I wouldn't recommend it as one to try unless you have a firm background in IDing gemstones in general and a lot of practice with this method on known stones or in a situation where you can try it and then back it up with further testing. It's a fun one though.

 

[Pandora II]

Is this something that you have discovered yourself through trial and error? If so then you ought to drop him a line and discuss it, could be very interesting.

 

[T L]

Are you talking about birefringence when you see this blue light? Some gems break up light in two beams along the pavillion facets when looking through a gem, and one of the beams can come back a different color than the primary color of the gem. This is caused by birefringence, but I'm not sure if that's what you're talking about, and I don't know if I would conclude it as a definitive test without proof. I have some pink tourmalines that do this, and you can see the blue flash, but it is not indicative of filling, as sometimes blue flash is indicative of.

http://en.wikipedia.org/wiki/Birefringence

 

[Michael_E]

If you see red/orange (in my experience after 100's and 100's of dollars in tests...), you have a "lead glass" filled ruby.

Sorry, but this method will not tell you anything about whether a stone has been glass filled. Seeing red/orange is normal for a ruby...the red/orange part of the transmitted spectrum is what makes a ruby red. Adding glass filling will not change the colors seen in the ruby spectrum unless the glass absorbs colors which would otherwise be transmitted by the ruby and that would change the color of the stone. The only way to see glass filling is to look at the stone through a microscope and look for the tell tales signs of filling. These are color flashes and filled surface fractures, with the filled surface fractures being very obvious after you've seen a couple of them.

 

[Michael_E]

Are you talking about birefringence when you see this blue light? Some gems break up light in two beams along the pavillion facets when looking through a gem, and one of the beams can come back a different color than the primary color of the gem. This is caused by birefringence, but I'm not sure if that's what you're talking about, and I don't know if I would conclude it as a definitive test without proof. I have some pink tourmalines that do this, and you can see the blue flash, but it is not indicative of filling, as sometimes blue flash is indicative of.

Birefringence causes facet doubling and the double rainbows seen in the previous image. It can be used to separate stones which are birefringent from those that are not such as ruby, which is, from spinel or garnet, which are not. Having different colors along different crystal axes is called dichroism and it is caused by different absorptions of colors along different axes. Even though they are not really related, I suppose that a strongly dichroic material could show slightly different colors in the doubled spectrums with the Hodgkinson method, depending on the entry and exit angles of light compared to each crystal axis. I've got to try this, as the color differences would change as the stone was tilted... might be neat looking.

The blue flashes seen in some stones can be caused by things other than filling. Some small inclusions can flash different colors as can twinning planes such as in moonstone or unfilled fractures in nearly anything. When viewed through a microscope, the blue flash from glass filling is very recognizable as such and an easy thing to pick out after you've seen a few of them, (particularly in colorless stones such as diamond). In filled stones the flash is not always blue. The interference colors seen depend on the width of the fracture

 

[soberguy]

Did anyone try it before commenting???? Just wondering....

 

[Richard M.]

Did anyone try it before commenting???? Just wondering....

That's what I've been wondering too. I use the Hodgkinson Method almost daily to check for items that aren't what they're supposed to be or isolate stones for more intensive testing. It's very helpful when buying stones without having the usual instruments available. I'll test your technique as soon as I have a known glass-filled stone to work with (I wouldn't buy one for any other reason). Your test makes some sense to me because glass in a fissure could easily change the internal optics of a stone by interfering with or blending normal spectral hues. If the method tests out it could be a very helpful as a preliminary caution flag.

Richard M.

 

[whatmeworry]

Did anyone try it before commenting???? Just wondering....

Doesn't work for me. I got red/orange in a quick test with a synthetic ruby.

 

[LD]

Didn't work for me also. Before replying I tested to see what I could see.

I have a number of Rubies and one that I know is filled. That flashed blue. According to the first post, this method means that the ruby is natural and not filled. That is absolutely 100% incorrect.

 

[Pandora II]

Didn't work for me also. Before replying I tested to see what I could see.

I have a number of Rubies and one that I know is filled. That flashed blue. According to the first post, this method means that the ruby is natural and not filled. That is absolutely 100% incorrect.

Just to check LD, are you doing the method to see the spectrum colours or are you looking for the internal flash off fillings?

I don't have any filled rubies to try it...

 

[LD]

Both. I tested both by holding up to a light and then by louping and rotating but with the light behind. It's actually quite difficult to do this test with set gemstones however as I think the light may not come through the stone correctly (or may be limited by the setting) - does that make sense?