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Author Topic: Specific Gravity test  (Read 463 times)

Percy1

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Specific Gravity test
« on: June 01, 2019, 06:27:08 PM »
Just new at identifying sapphires and was wondering if someone could explain what and how you do a Specific Gravity test thanks.

Aussie Sapphire

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Re: Specific Gravity test
« Reply #1 on: June 03, 2019, 05:54:01 PM »
Hi, 

If you download this document, it will explain the whole process:

http://aussielapidaryforum.com/forum/index.php?action=downloads;sa=view;down=9

Basically you need a good set of scales and a "rig" so you can weigh the stone in air and in water.  Use the calculation in the document to work out the specific gravity value - it is an excellent non-destructive id test.

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leah
Aussie Sapphire - The Lapidary Warehouse

roughcreations

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Re: Specific Gravity test
« Reply #2 on: June 16, 2019, 01:28:02 PM »
Just new at identifying sapphires and was wondering if someone could explain what and how you do a Specific Gravity test thanks.

This is the method I use - e.g. for aquamarine:

Weigh aquamarine: 2.06g


Tie some cotton to it


Zero a beaker of water on the scales


Measure the weight of the water displaced by totally immersing stone supported by cotton, just below surface, not touching anything: 0.76



Divide 2.06 by 0.76

Answer: 2.71

Walter Schumann Gemstones of the World says for aqua SG: 2.68 - 2.74

Bang in the middle!

MALACHI

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Re: Specific Gravity test
« Reply #3 on: June 16, 2019, 02:06:15 PM »
I like the way you have demonstrated the technique. It looks very simple to apply!
Cheers  beers

roughcreations

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Re: Specific Gravity test
« Reply #4 on: June 16, 2019, 05:57:14 PM »
Thanks, yes - simple and easy to apply, so encourages one to use the SG value more often as an aid to id. If you are doing the SG reading on a small faceted gem, it is possible to fashion a little sling out of cotton to hold it. The cotton is good as it absorbs water, therefore has little effect on the amount of displaced water. I doubt it would have any effect at all on the second decimal place anyhow, maybe the third or fourth.
RC

Percy1

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Re: Specific Gravity test
« Reply #5 on: June 17, 2019, 07:05:39 PM »
Thank you everybody for your help will try some of the techniques you have explained.

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