Precious Metal Testing: A Beginner's Guide
inNovember 20, 2007 - 1:48pm
If you buy and sell vintage and antique jewelry long enough, you will acquire some pieces that though unmarked, seem to be made of fine metal. Maybe it is their heft, their color or their style, but something tells you these are “better” pieces.
Many fine jewelry items of karat gold and sterling silver are not marked, either because of their small size or because they were made prior to 1906, when karat marking became mandatory in the US. In some instances, you may even find contemporary artist-made jewelry pieces that are unmarked for metal fineness.
In order to obtain the best price for your jewelry, it is essential to determine whether or not it is actually made of precious metal. All jewelry appraisers can determine the karat of an unmarked piece, as can many bench jewelers who routinely test unmarked items before making repairs. However, with the right supplies and a little practice, most jewelry sellers can learn to test their own jewelry items for precious metal content. It is a skill that can save you money at the jeweler, and make you money on the sale!
FIRST CLUES TO METAL CONTENT
As with any jewelry analysis, the first test involves visual inspection to rule out other metals. Using a 10x loupe or magnifier, examine the jewelry piece to see if there is a tiny mark hidden in an inconspicuous spot. And of course, be aware that the presence of a mark does not necessarily mean the metal in the item actually matches the mark. As in any area of antiques and collectibles, there are fakes both new and old.
Next, use the loupe to look for evidence the article is not gold or silver. Look first at the areas most likely to receive wear: the clasps on bracelets, the point where chain links rub together, the back surface of a pendant where it may have rested against skin. If you see brass or copper showing through in any areas, then your article is not made of either gold or silver and no further testing is necessary.
If your visual inspection reveals even color and tone to the finish of your piece with no areas of plate loss, then further testing is suggested. There are digital gold testers available, but most jewelry professionals rely upon the age-old acid or scratch test.
WHAT IS AN “ACID” or “SCRATCH” TEST?
Most jewelry professionals use the “Acid Test” or “Scratch Test” to analyze metal fineness. Testing kits can be readily purchased from major jewelry supply houses either online or in person. A basic testing kit consists of a wooden box containing three bottles of acid solution for testing 10kt, 14kt and 18kt gold. If you purchase your kit online or by mail, you will need to obtain nitric acid from a local chemical supply company to have a complete set of testing solutions. Also included in the kit should be a black basalt touchstone and a set of test needles. These needles are metal tapers tipped with gold of 10, 14 and 18 karat. (Test needles with a wider karat range are also available.)
If you have never conducted a scratch test, begin by practicing on items that you know are not made of precious metal. Scratch testing can be destructive if not carefully and properly conducted, so chose items of little value to practice on and hone your skills. In addition, remember to exercise extreme care in handling gold and silver testing solutions, as they are corrosive acids. In case of skin contact, flush with large amounts of water and sodium bicarbonate or baking soda mix. If swallowed, contact a physician or hospital at once. As with any other product that contains caustic chemicals, keep your test kit out of the reach of children and pets.
Due to the corrosive nature of the tests, you will also want to have an area prepared for testing. A piece of Formica, slab of marble, or old glass baking pan, covered with a white paper towel make good work surfaces. Make sure to mark the items clearly so that they are not accidentally used for food or other substances in the future. Keep a large cup of water with baking soda added at the test station should an emergency arise where you need to quickly neutralize acid that has come in contact with your skin.
Although acid testing requires you to take safety precautions, it is a valuable skill worth developing by serious jewelry sellers. In experienced hands, a scratch test is sensitive to within about +/- ½ karat. In the hands of a novice, sensitivity is more likely to be about +/- 1 to 2 karat.
HOW TO “SCRATCH” TEST GOLD JEWELRY
To test an object that you believe to be karat gold, draw the piece to be tested over the surface of the black touchstone provided, pressing well so as to leave a visible deposit, and making a line of one to one-half inches long. (Keep in mind that you need to bear down and make a heavy streak, in case the surface of the item alone is plated with precious metal.) Use the testing needle marked 10K to make a parallel streak just above the one made by your jewelry item. Place a drop of the 10K solution across both streaks. Compare the speed at which the scratches dissolve. If the test scratch dissolves more quickly than the needle scratch, the object is less than 10 karat gold or not gold at all. If the solution leaves the scratch intact, it means the object being tested is 10K or greater than 10K.
In the second case, clean and dry the surface of the stone and repeat the test with a fresh scratch from your object, a streak from the 14K test needle, and the 14K solution. If the solution dissolves the scratch on the stone, it means the object is less than 14K gold (if the scratch dissolves slowly and leaves rusty color particles, it is probably 12k gold). If the solution leaves the scratch intact, it means the object being tested is 14K or greater than 14K.
If the object has been determined to be 14K or greater, clean and dry the stone and repeat the test again with fresh streaks, using the 18K needle, and the 18K solution. Whenever the solution being used dissolves the scratch slowly and leaves rusty color particles it is probably two karats lower than the karat solution used.
HOW TO “SCRATCH” TEST SILVER
Testing silver requires the purchase of a separate acid solution, and does not require a test needle. This technique works for both jewelry and other silver articles such as flatware and hollowware.
To test silver, scratch the piece to be tested over the surface of the touchstone, pressing well so as to leave a large thick visible deposit in a line of one to one-half inches.
Transfer a drop of the silver solution to the scratch made. A streak from a sterling silver piece, with 92.5% pure silver, will turn the solution a creamy or milky white color. A streak from a piece of Continental or Coin silver, with 77% - 90% pure silver will turn the solution gray. If the solution turns green, or if there is no reaction at all, the item is made of some metal other than silver.
HOW TO “SCRATCH” TEST PLATINUM OR WHITE GOLD JEWELRY
Testing for platinum and white gold is similar to that of silver, but requires the use of yet another acid solution. Scratch the piece to be tested over the surface of the black stone provided, pressing well so as to leave a large and thick visible deposit in a line of one to one-half inches long.
Transfer a drop of the platinum test solution to the scratch made. If the material on the stone is platinum, it should keep its white, bright color. If the material is 18K white gold, the material on the stone should start changing to a light bronze color in about 3 minutes. For 14K white gold, the material on the stone should disappear in about 15 seconds.
NOTES ABOUT APPLYING ACID DIRECTLY
Although some jewelry dealers, historians and appraisers recommend filing into a piece to test, or dropping acid solutions directly on the item, these techniques should be avoided by all but the expert in metals testing as they are highly destructive. And though a gold-filled Victorian locket may not have the same value as a 14-karat locket of the same size and style, it still has value in the antique jewelry market. Careless or clumsy testing can destroy this value altogether. Nothing is more disheartening than finding an otherwise beautiful antique gold filled jewelry piece destroyed by an obtrusive file mark or a piece of vintage Mexican silver jewelry with a large, dull acid mark on the front.
If you master the basics of precious metal testing, you will find yourself recognizing unmarked jewelry with “potential” everywhere you shop. Just remember, if you are selling unmarked jewelry as having a certain composition or fineness in your e-commerce shop, you should mention your testing method in your description.