Part 6 of a series on metals. 

#7191 18k gold earrings. 

Some people get into a total tizz about whether their jewelry is 18k, a mere 17K or something else entirely. This may have a lot to do with the soaring price of gold over recent months. 

The term most people use for the metal value of an item of jewelry is 'MELT'. If we take a piece of jewelry, remove any gems and then weigh and test the resulting metal residue, we get the 'melt' value. 

It's true that there is a monetary difference in melt value between 9k or 22k, but there are other factors that in my opinion, override them. 
These include design, workmanship and gems.  Every jewel should be judged on its own merits and not according to the melt value of the metal.

#6818 22k gold emerald ring.  

If a typical brooch weighs well under 10grams, the difference in the value of the metal alone is not a whole lot.
Perhaps the lower grade metal is a lot stronger, more secure and will last a lot better than the more expensive metal.
Could the design and workmanship of the lower grade metal be as good, if not better than something made of high-grade gold? 

So, putting the melt value of a our jewelry into perspective, let's consider a few other factors.

As I mentioned last week, a lot of antique jewelry is not homogenous. Test one area and you'll get 18k, another spot says 14k and a 3rd something else altogether. 
The same item may have different components, some of which are not even precious metal, some are high value and others covered in enamel or dirt collected over hundreds of years. 

Overseas, in the UK and Europe, most auction houses will not specify the metal purity of an item of jewelry. They will mention if it is hallmarked, but you have to go through hoops to get metal information if the item is not marked. What I've been repeatedly told is that they do not want to commit to a specific purity. Testing metals is not as foolproof as one might think and they are open to huge liability if they get it wrong. 

Less responsible sources might use terms to indicate high value metal content, but they will not always stand behind such claims. Do beware.

#4282 14k gold earrings. jl-ear162-1a

So, HOW DO WE TEST METALS?  How do we measure their purity?

                               
 

There are people who claim that they can 'see' the purity of the gold. Ok, if the item is totally tarnished, you know it can't be high karat. Personally, I hold as much stock in the claim to 'see' the purity of gold as the even more outlandish claim of people who claim they can taste it. Yes, there are folks out there who explain that by biting the metal, they can tell whether it is 18k or less. 

In the old days, loadstones were used to divine the purity of metal. Since the metals we are interested in (gold, silver, platinum) are not magnetic, a jewel that was drawn to a magnet indicated high content of iron or other magnetic metals. 
For a long time, including the present, different strengths of acid have been used to test gold. 
Here is how it works: 
You scrape a little of the jewel onto a dark stone. It leaves a line of gold on the stone. You then drop varying strengths of acid on the resulting gold line. If the gold disappears, it means that the purity of the gold is less than the strength of that acid. You then try dropping less strong acid on the gold line until the gold remains. At that point you know what purity of gold you are working with. 
There are obvious disadvantages to this method. The acid may denature (weaken) with time and become less reliable; the gold might not be homogenous at different places in a jewel; it can be very difficult to get a good scraping of gold if the jewelry is very delicate or fine and finally and most importantly, scraping the jewelry leaves scars on your precious jewel. 

There are a number of more sophisticated technologically advanced systems for testing gold. Some use gels- really messy and the gels dry up. There are also a variety of digital testers, some more accurate than others. 

Even though I have acid and I have a digital tester, I usually take 2 more steps to test metal: I take it to an appraiser who has access to XRF technology (it's like a huge gun that gives metal purity results) or even to a pawn shop, where they have the most sophisticated metal testers. And YET, all of the above might not be entirely accurate. 

                                               

That brings me full circle to just how vital 100% accuracy is when testing metals. Yes, knowing the gold content is useful, but we should see it in proportion to the overall value of the design, gems and workmanship.
    

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