Ruby''s color indicate synthetic/natural?

[suchende]

I know synthetic/natural questions have been posed before, but I have searched and searched and not found the answer.

I have a ring belonging to a relative. I can't read the top half of the stamp, but the setting is either 10k or 18k white gold and there's what appears to be a J in a square, but it's so worn it's hard to tell, it may be in an oval or some other shape. It's a plain 6 prong setting.

It's a "diamond" cut, so it looks like a round diamond shape, I couldn't say if it most closely resembles a round brilliant or OEC or anything more specific. In indoor lighting it looks very dark, sometimes almost black. In sunlight or halogen lights, it sparkles some purples and blues. This darker color, not the brilliant, slightly orange-y red of my synthetic ruby, makes me wonder if it might indeed be a natural ruby.

I brought it into my local jeweler and told him the relative believed it to be a natural ruby. He examined it under a loupe (or maybe a microscope? His big, jeweler's equipment, I can't be certain) and said he would have to send it into GIA to be certain about it, but didn't find any obvious giveaways either way.

Any thoughts?
Thank you in advance!

Edited to add: I can't say exactly how big it is, but it faces up approximately as large as my 1.01 carat diamond (that is 6.5 mm) but it looks shallower.

 

[chrono]

Rubies come in many shades so colour alone will not tell you anything. Checking for a lack of inclusion and the type of inclusion will help somewhat. Another way to help guess is to figure out how old the stone is (to see if it matches up with when synthetics were first made).

 

[suchende]

It''s about 60 years old, so synthetics were definitely long since on the market.

 

[The Joker]

If I had a ruby I wanted checked out, I would send it to Richard Sherwood. Read this old thread and see why.
https://www.pricescope.com/community/threads/pink-sapphire-lab-or-natural.36589/

Joker....

 

[Pandora II]

How included is the stone?

If it''s very dark, I would be very surprised if it was synthetic. All the ones I have - from early versions through to modern have perfect ''ruby'' colour and are incredibly clean stones. If you look carefully you can also normally see the curved growth lines.

It could well be an almandine or pyrope garnet.

You could try buying a chelsea filter - both naturally and synthetic ruby will be brilliant glowing red (synthetic more so than natural), red garnets will be very dark red.

 

[suchende]

It's not included to the naked eye at all, I can't find anything under 10x and it's dark, but still very pretty, IMO. I originally suspected garnet, but now I'm convinced it's some sort of ruby.

I guess that's ultimately my question-- would a synthetic ruby that's 60+ years old be anything other than purest red?

 

[Pandora II]

What makes you think it''s not a garnet just out of interest?

I have never seen a synthetic ruby that didn''t look ''ruby red'' - my earliest known synthetic example is pre-1906 (jewellery is hallmarked with a date-stamp in the UK)

 

[suchende]

Well, for one thing my jeweler said it was doubly refractive, also the relative who owned it thought so, and when I hold it really close to my eye only red and blue fills my peripheral vision. Are there any other home tests?

I didn't know UK jewelry gets a date stamp, that's interesting!

 

[DiamondExpert]

Garnets are of the cubic crystal habit and therefore singly refractive, but the red garnets (rhodolite, pyrope, almandite) can appear to show double refraction in polarized light (ADR = anomalous double refraction), and even a good RI reading to separate corundum from Rhodolite garnet, which has the closest RI (~1.76) compared to corundum (1.762-1.770), can be difficult. So the optic character needs to be determined in polarized light for separation of true single refraction or double refraction from ADR.

Spinel, another possible candidate red stone, is singly refractive also, so that would be ruled out if the stone in question is found to be truly doubly refractive.

 

[suchende]

Interesting, thank you!