How Accurate is Acid Testing for Gold?

September 18, 2019

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How Accurate is Acid Testing for Gold?

Given that gold is both expensive and popular in nature, you can find many supposedly gold knock-offs on the market. This problem has existed for thousands of years with people reducing the real thing into various alloys. In fact, that's where the karat system comes from. In this article I discuss one of the basic ways to test gold: the acid test and how accurate acid testing for gold is.

There are multiple basic methods for determining gold's authenticity. Many of them have been around for as far back as the metal itself. Unfortunately, the age of a testing method tends to correspond to its accuracy. For instance, a money lender of 100 B.C. would have probably felt enough gold coins to be able to use the "skin test," i.e. feeling the density (weight vs. size) and warmth.

Unfortunately, this can be highly unreliable especially with the rise of counterfeit precious metals and currency. Next came hallmark (national and eventually private) and more recent "simple" ways of testing the shiny metal involve the use of magnets and water displacement.

Why am I writing about how accurate is acid testing for gold? For most readers involved in working with gold in any capacity, the acid test is the most affordable and fastest way of testing gold.

The reason that we can even ask how accurate is acid testing for gold, and the reason there exist multiple ways of testing gold is because of its chemical properties. Gold is long lasting and extremely stable in technical applications, and by extension in financial ones, for the following reasons and many more.

A Short Summary of the Properties of Gold (Au)
  1. Gold is resistant to oxidation - it does not rust.
  2. It is non-magnetic.
  3. Gold can conduct heat and electricity better than most elements
  4. You can only dissolve gold with nitro-chloric acid
  5. Technically, gold is extremely malleable, ductile, and sectile.

Because gold is sectile (you can split it by cutting), for instance, it needs to be alloyed with other metals. Gold's alloys are typically measured using the Karat System. One karat is the unit which is equal to the 1/24 part of genuine gold in the alloy. 24k of gold is pure gold. 18k gold is only 18 parts pure gold and 6 parts other metal (karat system).

Gold's purity can also be examined based on the millesimal fineness system, where the gold is indicated by parts per thousand of real gold by mass in the alloy. According to Canada's competition bureau, those items having less than 9K are not recognized as gold in a commercial sense.

Okay, so now you are familiar with gold's properties. Next, you probably want to find out whether your gold is "real or not." In focusing on whether or not it is accurate, it may be worth doing some reading about how to test for gold with acid before proceeding. If you've covered that, let's move on to how accurate is acid testing for gold.

Why Determine How Is Accurate Acid Testing for Gold?

If you've not read our article on how to test gold with acid, the gold acid test is the most popular and accurate tests you can do just about anywhere.  You can use it anywhere for jewellery or even as part of how to tell if a gold bullion is real. This is because it can only harm or damage fake materials. Please note that it is not advisable to use this test on jewellery that you plan on keeping or reselling. This test is recommended for scrap gold. The acid test is also the cheapest method used to check gold. A simple acid test kit usually comes with a black touchstone and several acid solutions.

You need to know how accurate is acid testing for gold for two reasons. First, because you want to figure out if gold is real and a false positive could sink you a lot of money. Second, you want to figure out exactly how much gold is in what you have or are buying. In other words, where does it fall on the karat or fineness scale? And most importantly, can you trust it?

So How Accurate Is Acid Testing for Gold?

Considering it traces back to the 8th century, using the "aqua regia" in the acid test is as much art as science. First, let's talk about technical precision. Acid tests have a relatively high tolerance. In other words, they are a good rough estimator of gold using the Karat scale, and even then, you shouldn't rely on it to the decimal point. Simply put, acid testing isn't always the most accurate.

Most acid kits contain materials to test 10k, 14k, 18k, and 22k gold. The acid rounds to the nearest testing solution. It will not tell you if it's 13k or 18.5k... Another problem with the acid test is that certain types of stainless steel may pass as 18 karat gold. As counterfeiting techniques are getting stronger and more advanced, it is becoming harder to spot. What we do is rely more heavily on the 14K acid and the 22K acid. That way you're testing two very different amounts of gold, rather than potentially having a murky distinction. More often than not, an acid test using 14K acid can tell the even lightly trained eye 10K gold. Likewise, a 22K acid will very clearly show you that something is not 18K whereas 18K acid is less reliable. But that's just my experience. Oh, and be sure to check that the acid is not expired.

A more technical point of not-so-common-sense is that for best results, let the acid eat into the gold. That is to say, cut into the metal or break it because the acid can't see what's inside.

Should You Go for "Safer" Alternatives?

It is essential to note that acid testing can damage the jewellery as you need to physically scratch it before applying the acid. The acid is also very corrosive and dangerous. You should wear gloves and apply care when performing the test. It can also be destructive to the metal if that metal is significantly lower than the acid's strength. Otherwise, acid testing is probably the most pragmatic method for testing gold.

When dealing with precious metals, accurate analysis is key. The XRF analyzer is a more advanced method for testing gold. It is very specific in determining which metal is in the jewellery. It is of course much more expensive and not a traditional "do-it-yourself" test. The XRF is what companies dealing with precious metals will most likely use. The XRF also does not go to deep into the metal, in fact only microns, whereas with the acid test, you go a little deeper. In both cases, cutting inside and testing that helps. Thus, the acid test is probably the most cost effective and accurate from all the "at home" tests. Just don't rely on it for precision.



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