I keep asking myself “is it just me?” or what the heck am I doing wrong? I posted some time ago about purchasing several hundred gemstones from a coin dealer who was buying jewelry for the metal and basically ripping out the stones with whatever was handy. Thank goodness only a handful of the gemstones were damaged and I was able to get the rest for a song… not once, but twice!
Now, I have all of these gorgeous, sparkly stones in a plethora of colors and yet, with the exception of a few, I have no idea what they are!
So, I got to work and learned how to do the SG test. I set up my jewelers scale, a SG testing kit and went to work! The results I came up with were no where close, well okay, they were sorta close… kinda… but they definitely didn’t fit within the numbers I found online. The numbers I found online were all consistant with no variations. I did have two that came out correct. Sapphire and Topaz. After these two matched up, I couldn’t get another match to save my life. I was testing KNOWN SAMPLES ONLY! I wanted to make certain I was comfortable with the results being accurate before I dove into the abyss!
Please help me! The kit I used was made of three long wires attatched to a circular wire at the top which held a cup for water( 70 degrees) this whole thing sits on your jewelry scale. Then, of course, before setting the cup of water into the holder, you weigh the stone dry, next, place cup into holder, zero out scale and weigh stone then do math. I used a pink topaz, diamond, sapphire, garnet and a ruby. Only the sapphire and the pink topaz were within their given SG numbers. The others were so far off it was ridiculous! I was tired, frustrated and terribly disappointed! I’ve tried this without the kit and haven’t had any luck either!
So, instead of asking myself, I’ll ask the community ~ Please ~ I need some help! I really need to know what these gemstones are. Its making me crazy 
Thank you so very much!
Hi Teri,
From what you have described, the test setup and procedure seems correct. Let’s look at this from the test setup perspective as we cannot build confidence in our test results, unless we have confidence in our test setup.
Does your scale have a calibration weight? If it doesn’t, you can purchase a set from various on-line venues. Amazon carries way too many versions to recommend a particular set.
The purpose of these weights is to verify the scale repeats measurements consistently and accurately. As long as your scale repeats consistently, you will have more confidence in the test result.
SG measurements can become very inaccurate measuring really small stones, if the scale can measure 0.001 gram or 0.005 carat precision, it should be able to measure SG for most stone sizes except for pave` or melee. Most portable “pocket” sized scales are less accurate typically down to 0.02 g. Which may not be accurate for stones less than 2mm in its largest dimension.
If you have confidence in your test setup with the above information, then consider the possibility that the SG measurement is telling you a different story about the stone. 
It is always fun to be surprised by the test results, especially when we have a pre-determined conclusion already in our mind of what the stone “should be”.
Cheers!
Part of the error could be that you are not taking into account the volume of the wire that supports the stone. Something to try: weigh the stone dry, then tie the thinest thread that you have (or hair) around the lump. Put a small cup of water (make sure that the cup of water will not exceed the capacity of the scale), zero the scale and dip the suspended stone in the water.
Possible sources of errors for this test include: resolution of the scales is insufficient (ideally you should be using something with a resolution of 0.01g); air being trapped on the wire; the capacity of the balance being exceeded (ie if the balance has a capacity of 50g, and the cup, water and frame weighs 48g prior to taring, putting a 5g stone in the water will likely exceed the capacity of the scale as the taring doesn’t extend the capacity of the scale); smaller stones will have a tendency to give greater errors; disolved solids in the water (ie salt) will throw off the result; this method is a bit of a fudge method.
Note that if you are doing the test properly (ie accrediated laboratory) the test would be undertaken in a density bottle with the test normally taking a couple of days to complete with multiple steps, some very expensive gear and very precise measurements.
Several testing devices exist.
About 7 various devices which help identify specimens of different types.
GIA has gold standard but you can identify on own with right equipment.
Most on market today floating about are Labratory grown gem stones mostly of Moissanite colors.
Do not get discouraged.
What are types of machines available?
Diamond tester works to identify conductivity or hardness upon sample.
Moissanite tester works to quickly identify moissanite samples goes immediately to Moissanite.
Other devices exist.
Each costing significant amounts of cost.
Diamond testers typically $10 because they fail so often and should be avoided.
More expensive option costs $500 or so gives better conductivity test.
Still not perfect.
Keep trying.
Stone looks to be a compressed granite with composition of other items.
Cut into layers for optional testing.
Most likely compressed mineralogy composite.
another source of error could be zeroing out between measurements. A picture of the device would be helpful… show it with and without the stone.
Thanks so much for your help with this! Also, I apologize that it’s been so long in getting back to you… geez! I can’t believe it’s been almost a year… actually, I got so discouraged that I finally decided it was time for me to get my gemologist certification and that’s what’s been taking up all my time… it’s definitely not for the faint of heart.
So okay, here’s where I left off: I am using a professional jewelers scale which comes with
Ooop! Sorry, I didn’t mean to hit that button! I wasn’t finished with my reply. I’ll continue…
My scale is a professional jewelers scale and it came with the calibration weights. I always make sure it is calibrated correctly each time I use it. I purchased a SG kit from Mineral Labs and make sure that it is set up properly and not interfering with the scale in any way whatsoever.
Next, I make sure to weigh the tool that I use to place the gem into the distilled water by placing it into the cup which already has the water in it and is already set up on the scale and zero it out. Next, I do the weight in air about four or five times to make sure I get appx the same readings, add all five together and / by 5 to get the mean #, and write down that number. Then do same steps for the weight in water. Then I do the calculations and go on to the next gemstone.
After doing a few I’ll come back and check the numbers against a paper I printed off of the GIA website.
I have learned while studying from my gemology certification that I should have been using distilled water with a drop of dish soap in it and I should also have had the water at room temperature or at least 70 degrees. I also remember reading that you can use baby oil to this test rather than using water.
I’ll be learning in my next unit, how to use my refractometer, my microscope, and my spectra- scope. Of course, these tools will all be wonderful tools in helping to tell me what gems I own and I can’t wait to get started on this next chapter!
Thank you all so very much for your great advice. I took everything you said to heart, combined what I could and was able to figure out that I had a couple of rare (very small, but rare) gems. I found 3 blue rubies, and 5 pink topaz. As I was going through the stones I came across a box that I had set aside, they were all unusual colors and I simply had no idea at the time, what to put them with. I am chomping at the bit to see what they are! I do know they are genuine because of the inclusions. The brilliance in each of the 5 is enough to take your breath away… I will let you know what they are as soon as I know! In the meantime I’ll attempt to do my very best to take pictures of them that will do them justice. If I can’t, then I won’t send them.
Again, many thanks…
Teri
Hi Teri,
Thank you for the response. Your scale and the apparatus from Mineral Labs is a good combination. Recommend doing the air test first, then the water displacement. This is to ensure the dry tests are not influenced by additional moisture from a wet stone or the SG apparatus. Adding a drop of dish soap to the water helps prevent air bubbles collecting on the stone. It does not take much. Just one or two drops of concentrated dish-soap in a gallon of water seems to work fine.
Water is my preference and have not tried another liquid like mineral or baby oil. Have read other suggestions to use an alternate liquid and its probably fine. Just not sure how temperature changes could affect the displacement volume of a different fluid. Water (distilled) for instance, is at its most dense value at four degrees Celsius (39.2F) and changes only 0.003 g/cm3 from 4 to 25C, a very small number. Not sure how other fluids behave with temperature. A reference article demonstrating the effect
As long as the setup environment doesn’t vary, the results should be fairly repeatable.
Looking forward to hearing how your next module goes with learning the refractometer, spectroscope, and microscope. They have their own unique challenges, but practice is the best way to become familiar with them.
Post any questions, if you find something not working or confusing.
Those blue stones you have, if they are corundum, they would be Sapphire versus Ruby.
Cheers!
-Troy
Hello Troy,
Thank you so much for responding. You don’t know how much I appreciate it. I haven’t really had a chance to look at my message to see whether anyone had answered me or not until now, so I wanted to let you know that you made my day!
I’ve been studying now for what seems like every waking moment for the last six months (and maybe a few of my sleeping moments too)! I did actually take some of the work with me to the beach but decided that was really pushing it and shoved it back into my bag! I mean, there ARE limits to everything right? I haven’t been in my shop for what seems like an eternity except to kill spiders! I HATE SPIDERS… so, I just wanted to let you know that I’m finally going to get that specific gravity kit out tomorrow morning and just DO IT!
Yes, apparently, at least according to your message, I have everything I need and the only thing I can do is do it. I have a pretty accurate list of gemstones and their specific gravity that I found on the GIA website (I’m pretty sure that’s where I got it anyway), and there was also one that came with the kit from Mineral Labs. If I have concerns, I’ll go with GIA.
I also have a couple of known gem species to start with. I’ll use amethyst, sapphire and blue topaz. I’ll make sure to check their SG’s are correct first …. So, again, thank you so much! I can’t wait to get started! I’d head down there right now but, I know myself too well and I wouldn’t come back up until sunrise…
So, I’ll finish watching the Seahawks play the Blue Jays, it’s a 3 - 4 game and Toronto just hit a three run homer a few minutes ago… IT’ A NAIL BITER… UHH OHHH BASES ARE LOADED!!! OHHH NOOO! WHO’DA THUNK IT? BLUE JAYS WIN !……BLUE JAYS WIN!!! BLUE JAYS WIN THE PENNANT! WHO CALLED IT? No, really… who called it? THE JAYS TOOK THE PENNANT!
Not that I care…. BECAUSE I’M A CUBS FAN! GO CUBS GO… GO CUBS GO… HEY CHICAGO WHAT YA SAY… CHICAGOS GONNA WIN TODAY… so.. okay, maybe not! But there’s always next season… we got heart 
Colts fan all the way all day!
Thanks again my friend. You’re the best!
Teri