How to Test Gold, Silver and Platinum
If you are not sure about your gold jewelry purity you can check it with a simple Gold Test Kit.
A simple test Kits include a test stone, set of gold test needles and testing solution acid.
The acid solutions include Hydrochloric Acid and Nitric Acid combined together since there is no single acid that can eat gold or platinum.
The test stone is usually black and is referred to as a touchstone. A touchstone is a small tablet of dark stone such as textured glass, field-stone, Slate or Lydite used for assaying precious metal alloys. It has a finely grained surface on which soft metals leave a visible trace.
When testing First check if there is a gold purity mark stamped on the jewelry to have an ideal of which solution to start with. Second choose an unimportant part on the jewelry and rub it on the touch stone until you can see a clear mark on the testing touch stone. Third if using test needles rub the nearest Karat needle next to the mark from jewelry to make a comparison mark. There is another option, if you do not have gold test needles you can use another piece of gold that you are sure of the purity level for your second mark. Fourth place a drip of acid with the Karat rating that you want to check. If the mark disappears or significantly changes that means the acid is dissolving the gold and the gold purity level is lower than the acid Karat rating of the solution. If the acid solution does not dissolve the gold then the gold Karat level is higher than the acid Karat level of the solution that was dripped on it and the metal is likely gold and you should test with a higher Karat solution.
Different Karat ratings:
•24 karat = 100% gold: usually considered to soft for jewelry
•22 karat = 91.7% gold: also soft and not recommended for jewelry
•18 karat = 75.0% gold: this level is usually recommended for fine jewelry
•14 karat = 58.3% gold: 14K is very popular and recommended for most jewelry
•12 karat = 50.0% gold: 12K is usually used for lower cost jewelry
•10 karat = 41.7% gold: The legal karat limit considered as real gold in the United States. Used in many low cost jewelry settings.
More interesting info on the solutions:
Gold Plating or filling:
With this test the jewelry piece will likely need to at least polish the piece up to a full repair of any damage done during the testing. It is necessary to guarantee the piece is real gold. To test for plating or filling I suggest to cut the piece to be tested in half and apply a drop of 14k test solution. Other less damaging but not as accurate ideas are use a test stone to rub deep in the metal, more then 6 millionths of an inch, to take a good test streak including inner metal to be laid down for testing on the touch stone. Another option is also to cut a small groove with a filed on an inconspicuous place of the jewelery and test. Some of the reactions you may see are, the object turns a bright green it is gold plated or gold filled on base metal. If the object turns a pinkish or cream color it is plated or gold filled on silver. 10 karat gold will turn dark brown. 12 karat gold will turn light brown. 14 karat or higher will have little or no reaction.
Testing White and Green Gold:
White and green gold react slowly, but will still leave a brown mark after applying acid.
Rub the article on the test stone and apply a drop of Platinum Solution. Platinum will not mark or tarnish and will remain the same white color with no reaction to the solution.
Rub the article on the test stone and apply a drop of Platinum Solution. If it is genuine, the scratch will turn red.
Rub the article on the test stone and apply a drop of Silver Solution. If it turns green, it is plated. If a cloudy cream, it is sterling or better. Remember, most Mexican silver generally contains less than 90% fine silver.
Testing Below 14 Karat and Base Metals with Schwerter Salts:
File a deep notch in the test piece and apply a drop of Schwerter’s Solution in the notch. The color reaction of the solution with the metal will be as follows:
Brass – Dark Brown
Copper – Brown
Nickel – Blue
Palladium – None
Gold – None
Silver Pure – Bright Red
Silver .925 – Dark Red
Silver .800 – Brown
Silver .500 – Green
Lead – Yellow
Tin – Yellow
Pre-Mixed Test Acids:
Pre-mixed gold, silver, and platinum test acids are available for those who do not wish to mix and handle acids. Generally a selection of these pre-mixed test acids are kept on hand to test for a variety of karats and metals. These acids can be used on test stones or directly on jewelry. If used directly on jewelry it will likely cause tarnish that will need to be cleaned and buffed.
Using Pre-Mixed Acids with a Test Stone:
Rub the jewelry on the test stone using firm strokes (two forward and two back) so that a very noticeable streak of metal is left on the stone
Apply a drop of pre-mixed acid to the center of the streak:
◦If the metal streak noticeably changes color or disappears than the metal is less than the test acid karat.
◦If the metal streak changes color only very slightly, then it has the same karat as the test acid.
◦If the metal streak does not change at all, than it has a higher karat than the acid.
Example: When using a 14K test acid, a 12K gold streak will exhibit a large, change color change or completely disappear, a 14K gold streak may have a very slight color change, and if the gold is higher than the 14K it will not change at all.
Using Pre-Mixed Acids on Jewelry:
Find a place on the piece of jewelry where you can file a small groove without ruining the jewelry – the intent is to penetrate the thin surface layer of plated metal ( if it is plated ). Try testing behind a link of a chain if you can – beware that it is not uncommon to use karat gold for clasps on chains that are only plated with gold.
Apply a drop of pre-mixed test acid in the small groove that you filed.
Note the color changes if any ( as above when testing on a stone)
Most jewelry pieces have areas of wear that can be good places to test. Occasionally the wear is sufficient to remove any plating and testing these areas without filing can confirm that the jewelry is a lower karat that the test acid. If you do try this and there is no color change, file a small groove and try again to be sure.
Test Acids Easy-to-use plastic bottles with, color-coded caps. Use with test stones or on a portion of the jewelry that has been sufficiently field to reveal the base metal ( if any ). Pre-mixed test acids are available for 10K, 14K, 18k, 22K gold, platinum and silver.
The test stone or touch stone can be used to test a streak of metal laid down from the jewelry, or a small groove can be filed on an inconspicuous place of the jewelry and tested.
Testing Silver additional information:
Rub the article on the test stone and apply a drop of Silver. The color reaction with the solution will be as follows ( take in to consideration that the background of the test stone used ) Remember , most Mexican silver generally contains less than 90% fine silver.
925 Silver – Dark Red
800 Silver – Brown
500 Silver – Green
Note: With the silver solution, it is possible to test directly on the piece being tested, however, the solution will dull the finish on the piece and leave a tarnish mark where the acid was placed.
Each bottle contains 1/2 fl. oz
The above information is for informational purpose and we do not guarantee results from testing. As with most things with practice you will become better at testing and get an eye for the results. Any new user should consult a professional before assuming any result is correct.
KEEP OUT OF REACH OF CHILDREN