August 24:—SAN ANTONIO, TEXAS: Retail show; Southwest Gem and Mineral Society of San Antonio; Sat. 10-5
Welcome to the GemologyOnline.com Forum
A non-profit Forum for the exchange of gemological ideas
It is currently Sun Aug 18, 2019 7:46 pm

All times are UTC - 4 hours




Post new topic Reply to topic  [ 29 posts ]  Go to page Previous  1, 2
Author Message
 Post subject: Re: Tutorial on Specific Gravity Using the Hydrostatic Metho
PostPosted: Wed Sep 30, 2015 5:03 pm 
Offline
Valued Contributor
User avatar

Joined: Wed Nov 12, 2014 4:12 am
Posts: 102
Yes i agree with you Stephen in all aspects, its modern technology, so as modern times, gemologists can now identify gemstones of their respective treatments and so as if they are synthetic, that maybe was not possible couple of decades back if i'm not wrong, i'm in gemology as well and would definitely seek an advice from experienced people like you.


Top
 Profile  
Reply with quote  
 Post subject: Re: Tutorial on Specific Gravity Using the Hydrostatic Metho
PostPosted: Wed Oct 07, 2015 11:42 am 
Offline
Valued Contributor

Joined: Tue Apr 30, 2013 1:41 pm
Posts: 172
Bill Hanneman wrote:
Nathan Renfro wrote:
Bill, I still don't understand why you think gemologists don't use SG anymore.

How about these reasons? :D :D

1. GIA does not consider SG a necessary instrument for basic gem identification. :(

2. I have never encountered a GG who could easily identify mineral specimens, i.e. faceting rough. :( :(

3. quote=Brabra Voltaire "… we all make mistakes. Specific Gravity is still a major pain in the butt for me. (Thank gawd for the gemmoraman.) …” =D> =D> :( :(
Quote:
I can confirm that myself, and all the gemologists I work with use SG every day. The wire basket is practical, which is why it is used, especially when measurements on several stones in a production environment is required.

It is interesting to note that in the latest Kassoy advertisement for Gemological Instruments, there is no mention of SG or how to measure it.
:smt003 On the other hand, they have shown nine different Scales, but not a single one claims to be useful for SG work, so I guess the secrete lies in the wire basket. I say eliminate it, as very few are interested in production. Use Relative Density. It is cheaper, faster, more easily understood and should be taught to all budding gemologists. :smt003

With the advent of Hodginson's new book, I believe GIA will be forced to revise their teaching methods of gem characterization involving SG, filters, dispersion, Luster, and B:D ratio. If I can be of any help, perhaps we should talk. Be aware, I have in little interest in artificial gems or appraising. I am only interested in what a matrial should be called. :D


Well Bill, it seems some clarification is order.

Regarding point number 1, it would seem that if the GIA didn't think SG were necessary for gem identification, they would have removed that section from their course material and spared the lives of a few trees. Also, if they felt it unnecessary, I imagine there would not be a hydrostatic scale in each GG classroom for the purpose of making SG measurements. However, there is information on SG measurements in the course material and a hydrostatic scale in each GG classroom, so apparently your impression of GIA and the importance of SG is not correct.

Regarding point 2, I have no difficulty in identifying rough material (for faceting or otherwise) and also am a proud GG. However, your claim has some merit as we have yet to actually meet.

Regarding point 3, I'm quite confident Barbra can make an accurate SG measurement especially now that she has her hydrostatic scale permanently set up.

_________________
Professional Gemologist and Microscopist

The views expressed here are the author's opinions and do not necessarily reflect those of the his employer.


Top
 Profile  
Reply with quote  
 Post subject: Re: Tutorial on Specific Gravity Using the Hydrostatic Metho
PostPosted: Wed Oct 07, 2015 10:20 pm 
Offline
Site Admin
User avatar

Joined: Sun Oct 16, 2005 12:22 pm
Posts: 19792
Location: San Francisco
:oops: Actually, I was able to take an SG on a bunch of stuff, now that I have a permanent set-up. Permanent scale, permanent H2O on standby.

Before it was a 3 part task.

FYI, The SG on that golden color glass which was sent to be with the cristobalite inclusions was 6.6. Wild!


Top
 Profile  
Reply with quote  
 Post subject: Re: Tutorial on Specific Gravity Using the Hydrostatic Metho
PostPosted: Thu Oct 08, 2015 2:43 am 
Offline
Gold Member

Joined: Mon May 14, 2007 11:00 am
Posts: 1133
Location: Monterey, CA
Could you tell us approximately how much it would cost to duplicate such a setup and how you get the value?


Top
 Profile  
Reply with quote  
 Post subject: Re: Tutorial on Specific Gravity Using the Hydrostatic Metho
PostPosted: Thu Oct 08, 2015 9:26 am 
Offline
Gemology Online Veteran

Joined: Sun Oct 29, 2006 11:43 pm
Posts: 518
Location: North Carolina
Bill,
For about $300 one can have the best of both worlds.

I have a Ohaus SPJ303 scale, good to 0.001g, The scale has a hook on the bottom that is connected to the weighing platform, so anything hanging from the scale is weighed. I put the scale on a little platform with an opening in the middle and hang some wire and a lower 'platform' from it. When I want to take a S.G. determination I put water in the container below the scale -- weigh the stone on the platform first; note the weight; zero the scale (with the stone on it); put the stone on the lower platform under water and the scale shows the difference in weight, air versus water. Divide the air weight by the difference and get the S.G.

I have successfully determined S.G. for stones as low as .3 carats, thought because it was strontium titanite the high S.G. might have made it easier than if it was lower density...

I am a faceter and I check the S.G. of any and all rough I buy, This setup makes it easy and I still have full use of the standard weighing capability with no fuss.

I have built your direct reading balance (pp 51-64) and found it easy to use, but it takes up a lot of room so I found myself clearing off a desktop and assembling the balance every time I needed S.G. readings. The Ohaus just needs to have water added to the container AND is a good milligram scale.

_________________
Bob K.


Top
 Profile  
Reply with quote  
 Post subject: Re: Tutorial on Specific Gravity Using the Hydrostatic Metho
PostPosted: Thu Oct 08, 2015 11:07 am 
Offline
Site Admin
User avatar

Joined: Sun Oct 16, 2005 12:22 pm
Posts: 19792
Location: San Francisco
I got a GemOro Scale $89
http://www.amazon.com/GemOro-Platinum-P ... B00A4LII4A

Checking accuracy with my Metler.

And this gizmo from Mineralab for $89:
http://www.mineralab.com/Scale.htm


Top
 Profile  
Reply with quote  
 Post subject: Re: Tutorial on Specific Gravity Using the Hydrostatic Metho
PostPosted: Thu Nov 05, 2015 3:25 pm 
Offline
Gold Member

Joined: Wed Sep 02, 2015 10:52 pm
Posts: 1131
Location: Central Queensland, Australia
Thank you Barbra, these are exactly the sorts of things I need to understand how to perform, given the amount of digging for different things in different localities that I do. I have seen various methods but they seemed much more complicated than the ones in the video and I wasn't certain of the accuracy of my scales (I had only kitchen scales back then, I have much better ones now).

Interesting and unusual things pop up, often when you're looking for something else altogether. The more basic tests I can do at home, the better and the more information I can provide to accompany photos.


Top
 Profile  
Reply with quote  
 Post subject: Re: Tutorial on Specific Gravity Using the Hydrostatic Metho
PostPosted: Sun Nov 22, 2015 7:51 am 
Offline
Gold Member

Joined: Wed Sep 02, 2015 10:52 pm
Posts: 1131
Location: Central Queensland, Australia
I must be a bit of a dunce, I can't get any of these methods to return a value even remotely close to that of materials I already know the identity of :( Quartz is rather heavier than 1.8 and zircon a lot heavier than 0.4.

My scales seem pretty accurate but I'm having some difficulty seeing exactly what is happening in the photos and video - the water vessel in which the stone is suspended in the video does not appear to be actually touching the scale.


Top
 Profile  
Reply with quote  
 Post subject: Re: Tutorial on Specific Gravity Using the Hydrostatic Metho
PostPosted: Sun Nov 22, 2015 8:48 am 
Offline
Gold Member

Joined: Wed Sep 02, 2015 10:52 pm
Posts: 1131
Location: Central Queensland, Australia
Edit: these scales are not very accurate and/or my crude approach is affecting the result further.

3 tests on a known piece of quartz returned 2.44, 2.42, 2.35 - quartz should be 2.66?

a known topaz crystal returned 3.45, 3.18, 3.08 - should be 3.5

A known sapphire returned 3.70, 3.26, 3.00 - should be 4.0

A known zircon returned 3.62, 3.58, 3.59 - should be 4.6

A piece of unknown material that closely resembles a colourless zircon returned 3.30, 3.26, 3.26

I think I need better scales for starters


Top
 Profile  
Reply with quote  
 Post subject: Re: Tutorial on Specific Gravity Using the Hydrostatic Metho
PostPosted: Sun Nov 22, 2015 10:24 pm 
Offline
Gold Member

Joined: Mon May 14, 2007 11:00 am
Posts: 1133
Location: Monterey, CA
Lefty wrote:
I think I need better scales for starters

You are wasting you time.You don't need a scale to determine density. You can make your own relative density balance for less than $5. :D :D No weights, unlimited range, and direct reading.


Top
 Profile  
Reply with quote  
 Post subject: Re: Tutorial on Specific Gravity Using the Hydrostatic Metho
PostPosted: Wed Nov 25, 2015 10:27 pm 
Offline
Gold Member

Joined: Wed Sep 02, 2015 10:52 pm
Posts: 1131
Location: Central Queensland, Australia
Well I did the test again, this time making sure the ceiling fan was off and the air in the room was still. Same unknown stone returned three readings very much closer together, consistent with the SG of topaz. I haven't gotten around to doing a bunch of known stones again yet, busy trying to finish a stone for someone. I'll have another play when I'm finished.

Can you tell me meore about this relative density balance Bill?


Top
 Profile  
Reply with quote  
 Post subject: Re: Tutorial on Specific Gravity Using the Hydrostatic Metho
PostPosted: Fri May 10, 2019 2:07 am 
Offline
New to the Forum or The Quiet Type

Joined: Mon Apr 15, 2019 10:45 pm
Posts: 8
So here is another really dumb question. Why go though all the fuss and why not just drop the stone in a vial of water after it is tared out? Do you really need wire holders, etc.?

Thanks,
Mitch


Top
 Profile  
Reply with quote  
 Post subject: Re: Tutorial on Specific Gravity Using the Hydrostatic Metho
PostPosted: Fri May 10, 2019 2:23 pm 
Offline
Moderator
User avatar

Joined: Mon Apr 02, 2012 9:31 pm
Posts: 3354
Location: North Carolina
That does not work. The stone's weight does not vanish in water, if it is not supported by anything all the weight is pushing down on the scale whether it is in or out of water.

_________________
https://www.etsy.com/shop/angryturtle


Top
 Profile  
Reply with quote  
 Post subject: Re: Tutorial on Specific Gravity Using the Hydrostatic Metho
PostPosted: Fri May 10, 2019 3:14 pm 
Offline
New to the Forum or The Quiet Type

Joined: Mon Apr 15, 2019 10:45 pm
Posts: 8
Yeah, when I woke up this morning, I realized that I was having a "Senior Moment" when I posted this, but it was too late to stop it :-)


Top
 Profile  
Reply with quote  
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 29 posts ]  Go to page Previous  1, 2

All times are UTC - 4 hours


Who is online

Users browsing this forum: No registered users and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
Powered by phpBB © 2000, 2002, 2005, 2007 phpBB Group
Gemology Style ported to phpBB3 by Christian Bullock