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.