Antique & Vintage Jewelry : How To Test for Gold Content

March 15, 2018

Scratch Testing Gold - What is not written on the test kit instructions

Over the years of buying lots, jewelry boxes and estates, little bits and pieces of Antique and Vintage jewelry accumulate. Some of it can be solid gold, some of it can be just plated or gold filled.

Sometime ago, I decided to cash in on these and sent them to my trusted buyer to be melted. There was quite an amount and I thought I was in for a small treasure. Much to my disappointment, 1/3 of it was not solid gold! I had tested each tiny piece by scratching it on the test stone, following the given directions and it had reacted as gold should, so how come it was not right?

As it turns out, rubbing the piece or removing shavings from it is not a sure way to test. Read on and I will share my secret.

The Basics:

It is important to note that gold filled or rolled gold and gold plated are not the same. They are very different and have very different values. Gold filled or rolled gold actually has a gold content. The gold content in plated jewelry is negligible.

The process for making Gold Filled is similar to making a sandwich. One or two sheets of gold and one sheet of base metal are layered. Generally speaking, brass is used for Yellow Gold Filled and Copper is used for Rose Gold Fill. If two sheets of gold are used, the base metal will be in the middle (like a sandwich). The sheets are then heated and passed through a rolling mill, hence the name rolled gold. The heat and pressure cause the sheets to bond permanently.

Gold plated is a different process all together. The jewelry or metal piece is attached to a wire on the negative side, a piece of pure gold is attached to the positive side of the same wire. The two ends are submerged into a special liquid (plating solution). A low voltage current is then applied. The current causes gold molecules to move from the pure gold to the surface of the metal being plated. Older antique and vintage jewelry tends to have a thicker layer of gold, but as you can tell from the process itself, that layer is still very thin, generally 7 microns for better quality. Nowadays, most plating is done with a maximum of 3 microns. A micron is one thousand of a millimeter. That's really thin!

Back to our testing for gold and silver content with an acid test kit.


First let me start with a very big warning:

Use extreme caution! Always follow test kit manufacturer instructions and use loads of common sense.

  • These chemicals are dangerous, they are acids and very destructive, they burn the skin and surfaces of furniture.
  • Do not leave where children and pets can reach them.
  • Work in a well ventilated area. Do not breath the fumes or stand with your face right above the testing area. Do not let it splash.
  • Wear goggles to protect your eyes. Do not get it on your skin!
  • Do not allow testing liquids to touch gemstones, enamel or any ornamentation on the jewelry.
  • Always start with the 10k Gold Testing Solution and go up from there as described below.
  • If the piece is of lower than 10k it might be damaged as well.

     

    Testing for gold with an acid test kit:

    Clean the piece well. Examine every area of it carefully with a jeweler's loupe. If you see that the edges or high profile areas are a different color you can probably stop there, the piece is gold plated. Another sign to look for is the quality of manufacturing. For instance, very rarely you will you see gold necklaces that do not have soldered links. I have never seen one, all of the vintage and antique gold necklaces I have had had soldered links.

    Look for quality marks. I test all jewelry, even when it is marked. Until the 1980s it was acceptable to have some variation on the gold content per karat. So you may come across jewelry marked 14k that might have a content as low as 12k! Once or twice, I also tested jewelry fully marked 14k and it was just plated.

    Now you have looked at the piece carefully and there is no indication that it is plated, no costume jewelry company name on it, no metal quality mark. We go to the next step.

    Some very important things to keep in mind:

    The acid can destroy or at least damage the piece of jewelry tested if it is not solid gold. Be extremely careful and try to find an area where it will be seen the least. Make sure to have a clear surface for the test stone. Have some Baking Soda handy to neutralize the acid right away. Place some in a shaker or small cup, have it with you while testing.

    Because gold filled has a thick layer of gold, rubbing it on the test stone is sometimes not enough to determine if a piece is gold filled or solid gold. My experience is that the older it is the thicker is the layer of gold.

    You need to make a tiny incision in a hidden area. Using a single edge razor blade, carefully make a small but fairly deep cut, no bigger than 1/16" . Take care not to go through it! What you want to do is to get to the metal underneath the surface layer. At that spot, drop the smallest of drops and wait a second or two. If it turns green you can stop, it is gold filled. It will bubble like crazy. As soon as you see the green color throw some baking soda on it to neutralize the acid. Do not breathe any fumes. Then wash the piece well and polish with a Sunshine Cloth (not affiliated, just think it does a great job). If instructions are followed carefully you should have no problem returning the piece to it's original condition and removing all the marks, if any, left by the testing liquid.

    If you had no reaction with the gold testing acid, congratulations! The piece is solid gold and now we will determine what karat it is.

    Take the test stone that comes with the kit.

    Choose an area on the jewelry you want to test that is not easily seen. Rub it carefully and evenly to create a fairly healthy streak on the stone. Avoid keeping the same spot against the stone as it will sand down the surface. Drop the 10k Gold Testing Liquid on to the streak on the stone. If the color of the scratch remains unchanged, it is 10k or higher. Proceed by repeating the process using the 14k Testing Solution. If the scratch color remains unchanged, it is at least 14k and you should repeat the process with liquids for 18k and until 22k or 24k solution, whichever is included in your test kit. When the color changes from one step to the next the last karat solution which caused no change is the karat gold for the jewelry you are testing.

    It is always good to replace the test kit with a new one about every 6 months. I have been told the liquid gets stronger with time, which would cause a karat reading lower than the actual karat weight of the jewelry being tested.

    And one more reminder: Use extreme caution and loads of common sense!

    Please also note that I am not responsible for any mishaps that might occur. This is how I do it and I am just sharing my experience. There maybe a better way for you. And if you do not feel comfortable doing this, by all means, bring it to your trusted jeweler and have him or her do it for you.


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