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 Post subject: Help me identify?
PostPosted: Sun Sep 24, 2017 6:56 pm 
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Good day everyone. I just got started in gemmology and I'm reading Beginner's Guide to Gemmology by Peter G Read. Right now I'm about 40% through. It's a bit challenging (it doesn't illustrate most of its explanations so I'm not sure what it means sometimes) and well, sort of outdated but I'm managing (on a tangent, if someone has a recommendation for a better book I'm all ears).

I got into gemology because I make jewelry. The non-fine kind, with jump rings, wire, acrylic, etc. But I want to get started in stone setting in silver. I decided to buy some Cubic Zirconia from a Chinese provider a while ago. I still have the samples (50 2mm round cut clear pieces and a 5mm round piece from another manufacturer). Recently I've thought of purchasing more and got a quote for a larger order (different cuts, sizes, etc.). However, today I was studying some more on gems and it occurred to me that I might not have ordered CZ at all.

I began examining the stones, but it's really challenging. I ran the culet of one sample across glass and I couldn't notice any scratches on either piece (keep in mind I pressed it with my finger; I don't have tweezers to hold them). I then dragged it across plastic with the same results, so this test proved non conclusive for me. I have some thread counter loupes and a vernier, but the loupes are mementos so I can't create a makeshift calibrated microscope to check the refraction (also I don't see the difference between focusing it on the culet and on the table, if it makes sense). I also checked it under one of those UV light bug zappers, and it kind of shone white with the faintest of blues.

As for the "fire" of the stone: I have never ever seen a CZ tagged as such in a jewelry so I'm not sure what I'm looking for. But my stones shine white under a LED light. They display a few more different colors under the sun, though.

As for the density, I know a 5mm round cut CZ should weigh more or less .5ct but I read flint glass can have a similar density. I'll still weigh it tomorrow when I go to college. I'll also see if we have a short wave UV light to test if the stone shines brown or yellow, and take pictures. I can upload the pictures I've taken so far if requested, as well.

Does anybody have recommendations of other tests I can try, or know if this is indeed just glass? I don't really have much money nor access to a gemologist and just started building up my tool set. I'm tempted to order one of those natural faceted stone sets certified by the GIA but I'm not American (shipping+tariff costs) and anyways the carat is pricey for my budget.


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 Post subject: Re: Help me identify?
PostPosted: Sun Sep 24, 2017 7:22 pm 
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Hi Glasspremia and welcome to the forum.
Cubic zirconia is quite inexpensive to manufacture, so it is unlikely that you got snookered.

1. Forget the scratch test. You can cleave a diamond by trying to see if it will scratch glass. Anything of equal hardness will scratch itself. Glass will scratch glass. *

2. The specific gravity of CZ is between 5.65 and 5.95.
Yttrium stabilized cubic zirconia: = 5.95
Calcium oxide stabilized cubic zirconia: = 5.65

Diamond's specific gravity is 3.52. That makes CZ approximately 1.7X denser.
Therefore, a 5mm diamond weighs just shy of 0.50ct....a 5mm CZ would weigh approximately 0.85ct. (.50 x 1.7=0.85)

When CZ is viewed with a small light from the backside, it will show a monochromatic orange flash on the pavilion:
Image

These clues should help.

* Hardness tests should only be used when you don't care if you destroy your unknown. Use hardness points to scratch the unknown, not the unknown to scratch other stuff.


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 Post subject: Re: Help me identify?
PostPosted: Sun Sep 24, 2017 7:42 pm 
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One more thing, may I suggest you download the Handbook of Gemmology

You will never regret it!


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 Post subject: Re: Help me identify?
PostPosted: Sun Sep 24, 2017 8:00 pm 
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Thank you for your welcome and your response, Barbra. I'm worried mostly because I read flint glass is cheaper than CZ and other suppliers of synthetic gemstones quoted greater prices for a stone of similar size, color, cut, and supposed quality. The 5mm round cut ones cost me $0.028 (USD) each, or basically 3 cents. Meanwhile another retailer is listing them for $0.28 USD.

I don't mind breaking the stone. The 2mm ones were bought on a whim and it's unlikely I'll be able to mount them properly (I only have my dad's tools at my disposal, and he's not even remotely close to a jeweler). So if there are any definitive tests I can conduct that might break the stone I would love to know.

Oh god... I checked size by carat tables for CZ and they stated it was .5ct. Now I'm checking the diamond ones and they say the same. You're right then; it's gotta be 0,85ct. I'll check for that.

As for the orange flash: I have used my phone's flash and a LED flashlight but at most I can see a bit of a rainbow shine. What sort of small light should I use?

Also, I forgot to mention: it does this to a dot. Not sure if glass also behaves like this:

Image

Thanks Barbra. With the recent purchases I made I'll be a bit tight of hobby money these days but I'll definitely buy that one when I get some more :)


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 Post subject: Re: Help me identify?
PostPosted: Mon Sep 25, 2017 1:59 pm 
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glasspremia wrote:
Does anybody have recommendations of other tests I can try, or know if this is indeed just glass?

Touch it to your tongue.


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 Post subject: Re: Help me identify?
PostPosted: Mon Sep 25, 2017 2:36 pm 
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Thank you for your response.

I rinsed the 5mm one because God knows how much stuff I've dragged it through in my tests. Then I dried it off. It felt really cold against the tip of my tongue, so I'm guessing it is glass after all. Again, I've never licked a gemstone so I'm not too sure. But since it shines white and was pretty cheap I guess I got duped.

I'll be able to weigh it in a couple of hours.

I'm still waiting for an order to arrive (you could tell me Mexican couriers travel by giant tortoise and I'd believe you). It cost me a few bucks for 100 5mm round cut clear pieces. Fortunately the larger order hasn't been paid yet (which frees up some money for the book!). I wasn't going to order after all because I wanted to buy through Amazon and the seller didn't make a new post for my order, but linked me to a listing of a cheaper item and told me to buy it 10 times (for a total of 1000 6,5mm round clear cut "CZ" instead of 2000 assorted color and cut 3mm - 14mm pieces). Seemed risky to me; not sure what the Amazon policy would be if I had a complaint.

Reading through the forum I heard Mod Barbra sells stones, but the link to the shop was defunct or otherwise unavailable (I can't remember). Are there any approved sources for a newbie like me where I can buy an assorted lot? My little glass gems look great and all but I don't want to support a possible scammer. Plus I feel it wouldn't be too educational anyways... can I get faceted stones for cheaper than $0.12 the carat, or should I get the ones at that price? They're apparently pretty bad quality but suit my purposes.


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 Post subject: Re: Help me identify?
PostPosted: Mon Sep 25, 2017 4:12 pm 
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You have Dr. Hanneman's suggestion backwards.
Glass is warm to the touch, stone cold.

The weight should be definitive.


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 Post subject: Re: Help me identify?
PostPosted: Mon Sep 25, 2017 8:22 pm 
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Thank you very much for all your help, guys. You've been really attentive.

Sorry. I read CZ was an insulator on Wikipedia so I assumed it worked that way. Looking at the thermal conductivity tables it seems both have very low values (~1 or below for glass, 1.7-2.7 for CZ)... Maybe it was cold because I ran it through water first. Just now I pressed it against my lips and it still feels really cold, though, but again: I'm not sure what I'm looking for.

I estimated the SG of the stone and it's 5.55 going by the "Estimating the Carat Weight of Mounted Gems" link on this forum and 5.73 going by a diamond size chart and using the SG of reference of 3.50. I'm not sure how good the Vernier I used is -I did buy it from China...-, but it measured up to 2 decimal points of a milimeter. Seems the density does check out.

I'm so confused :oops: . I think I'll just get the natural ones and practice with those in the meantime.


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 Post subject: Re: Help me identify?
PostPosted: Mon Sep 25, 2017 10:22 pm 
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Please supply the mm size and the actual weight of a stone.

I'll explain how to get the specific gravity using that information.


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 Post subject: Re: Help me identify?
PostPosted: Mon Sep 25, 2017 11:14 pm 
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Oh, thank you very much! I was wondering if I had used the units wrong when applying the formula; it took me a bit of fumbling around.

Round cut:

5.05mm diameter
3.07mm culet to table
.15~.16 grams (digital scale kinda flickered between the values and didn't give me any more digits, sorry for the inaccuracy).

Please don't be lead glass, please don't be lead glass...


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 Post subject: Re: Help me identify?
PostPosted: Tue Sep 26, 2017 12:12 pm 
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There are 5 carats in a gram.
0.16 X 5= 0.80

Your 5 mm unknown weighs approximately 0.80 carats.

If diamond the 5mm would weigh 0.50
0.50 x 1.7 (The correction for cz) = 0.85

Taking into consideration that your gram scale is not as accurate as a calibrated carat scale, I'd say you have CZ.


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