plating, anodizing, & finishing Q&As since 1989
Specific gravity table for gold
Danib, specific gravity is not an accurate way to determine purity of gold. The element tungsten has a very high specific gravity (19.22). While it is very close to that of gold (19.32), it is a relatively cheap metal. A bar of nearly pure tungsten could be coated with a thin layer of pure gold, and it would fool many experts into believing the entire bar was close to pure gold using any type of specific gravity method. It is helpful as a double check but not for certainty.
The most accurate ways to determine gold's purity is for it to be melted down and separated from its base metals or to use an X-ray Spectrometer device specifically designed to analyze its alloy concentration. These are very expensive -- in the multiple thousands of (USD) dollars to purchase.
There are even companies that specialize in making tungsten jewelry plated with gold!
- Woodburn, Oregon
January 12, 2023
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Q. After I melted my unused jewelry and make it into gold bar, how do I know how much percent that gold is it? I use specific gravity theory. And I need the table of specific gravity. eg. 19.33 for 99.99% of gold ... I need complete table from 10% of gold until 99.999% of gold.
Thanks.Jendy M [last name deleted for privacy by Editor]
A. This method will not work if more than one alloying element is present.
Different alloying elements have different SG's, e.g., 8.90 for cobalt and nickel, 8.94 g/cc for copper, 10.49 for silver, 12.0 for palladium, 12.4 for rhodium, 21.45 for platinum, etc. It is possible for alloys of different gold concentrations to have same SG, and for alloys of same SG to have different gold content. An alloy of 83 vol.% platinum and 17 vol. % copper will have roughly the same SG as 100% gold. Even knowing the composition (wt.% or at.%) of a multi-component alloy, it is difficult to accurately calculate the exact SG because non-ideal thermodynamic interaction of atoms will affect the volume. Porosity is another problem.
From an Internet search, you can find data for simple alloys such as gold-silver and gold-copper. But because of multicomponent effects noted above, 9 carat gold has SG range 10.9-12.7, 18 carat yellow gold 15.2-15.9, 18 carat white gold 14.7-16.9, 22 carat 17.7-17.8, sterling silver 10.2-10.3.
The World Gold Council (www.gold.org) describes methods of analysis under heading assaying. The density method is listed as poor for accuracy and only for binary alloys.
- Goleta, California
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A. I have been testing items for gold content for many years now and found using a grain scale a fairly accurate specific gravity (SG) can be attained enough so that the tester will know if the item has gold in it. Like the last article stated without knowing what other metal has been used it is hard to judge carats. I assume copper as second metal being most common and if my test comes back with a SG over 12 I am reasonably certain it is gold most tests of jewelry have a SG of 12 to 14 meaning gold in the range of 10 to 14 carat. Very seldom have I been mistaken. Tonight I just finished a SG test on a ring with the SG of 15.3 tomorrow I will find out if it 18 carat gold as my test showed. It may not always work but a SG test is an inexpensive means of testing gold.no chemicals or damages to item just a grain scale thread and a glass of water.Robert S [last name deleted for privacy by Editor]
- Tujunga, California, USA
Q. Dear All,
I have been asked to develop a software to test gold purity. We don't know anything about possible metals and their combination alloyed with that particular gold bar. But still they are using this software for testing gold purity commercially in Gold test laboratories. I am sending you few calculations.
First Weight (Dry Weight) 7.808 gm
Second Weight(Suspended spring scale in water) 7.384 gm
Total Impurity 0.3368 gm
Total Pure Gold 7.4712 gm
First Weight (Dry Weight) 10.3340 gm
Second Weight(Suspended spring scale in water) 9.783 gm
Total Impurity 0.3365 gm
Total Pure Gold 9.9975 gm
Any help will be greatly appreciated.
July 30, 2012