While metal detecting in the fields of Europe, I often find coins and artifacts from a time period stretching over 4,000 years. Most of the copper alloy finds have a green verdigris patina, silver is grey and gold is usually gold colored. On some occasions I find an item that appears to be un-hallmarked gold, but because of ground conditions I can’t always be sure.
Fig 1 Roman oricalcum coin from waterlogged silt.
So over the years I’ve amassed a collection of finds that I believe to be gold, but have never been able to reliably verify. I’ve tried an acid tester (Fig 2) with little success. I didn’t like the idea of rubbing off a small amount of gold onto grit paper, to add acid too. So when Minelab announced they were releasing the PRO-ALLOY Gold Purity Tester, I jumped at the chance of testing one.
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| Fig 2 Acid testing kit. | Fig 3 PRO-ALLOY tester, case and leads |
The tester comes packed in a black padded nylon case, with instruction, two leads, a probe and a crocodile clip. The probe is filled with a clear liquid that lubricates the contact area of the probe to test item. It’s important to replace the probe’s cap after use, to prevent premature drying out of the fluid. Once the fluid is used up, a replacement probe will need to be purchased (part number 3011-0309).To use the PRO-ALLOY, connect a RED lead to a positive “+” socket of the meter. Then connect the other end of the lead to the probe. If you are going to place the test item on the silver area of the tester (Fig 4), it is not necessary to connect the black lead.
Fig 4 Silver area, controls and sockets Fig 5 18-karat gold ring calibration
Calibration
Pull off the probe cap and place an 18-karat gold item onto the silver area of the meter. Switch on the tester and touch the probe onto the gold, and adjust the meter needle so it settles at the half waypoint of the 18Kt segment. The meter is now calibrated and ready to be used.
One question I’m often asked since posting the video (below) on YouTube is; “what reading do you get on gold plated items”? I’ve tried a few items with a thin film coating of pure gold, and the results were all in the 10Kt area of the meter. So if you are testing a known gold item, but get a much lower result than expected, then this could be a good indication of a fake gold plated item.
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