Does anyone have experience with test results of specific gravity? I have tested two so far, 1 ounce cast bars of gold from one of the smaller Australian manufacturers of gold bars. One bar has a specific gravity of 19.33 and the other tests as 18.75. Both bars are stamped GOLD 9999. Could this bar with the specific gravity of 18.75 actually be only 96% pure and 29.8 grams AGW or could there be another reason like an air bubble inside the gold?
depends if u using tweezers or .. to put the coin in the water also u have to make sure u control all the variables for both and that you be careful not to make any errors in reading, scale has been zeroed etc. one last thing is u said its a small manufacturer ; maybe they are not as pure as they say
You have to correct for water density which changes with temperature. You'll be able to find tables on the internet somewhere... http://www.simetric.co.uk/si_water.htm I would only bother going to 3 decimal places. for example water between 29-30deg = .995g/ml 26-28deg = .996g/ml 21-25deg = .997g/ml Also remove any airbubbles that may appear on the sample or your tweezers etc.
Thanks for the tips all, I have done a second round of measurements, this time with four bars from the same manufacturer and a sovereign and a 24k ring. I even went as far as using two strands of hair to suspend the first bar in the water but I like the glad wrap idea and will try that on the next measurement test. The sovereign was only measured with tweezers, the ring was suspended with a hair. I have three digital scales, two are 100g at 0.01g accuracy and the third is 20g at 0.001g accuracy and a 10g reference weight to calibrate them. I performed the tests as controlled as possible with my current understanding. 1oz cast bar 31.14 18.759 1oz cast bar 31.13 19.335 1oz cast bar 31.13 19.21 1oz cast bar 31.14 19.342 1967 sovereign 7.997 17.384 24k ring 12.970 19.35 I still need to correct for temperature with the above numbers but this shows the first bar still does not seem dense enough in comparison. Is the third bar at 19.21 ok? What would you do? I will be taking this first bar into them sometime soon and have a quiet chat with someone I know from there who works behind the sales desk.
Air bubble sounds most likely but since it has correct weight its an easy question of purity. An acid test or better XRF will settle your question. If the sellers allow it you could swap it for another and not bother with it further. Also is the reason I never buy any bars other than pamp or Perth mint.
Take those (under 19.25 ) back if you can and swap em for some other ones, and kindly explain to them why. If they decline you, than come back here and let us know.
