Fine wristwatches have always been offered in gold cases. While those of us with decades of daily involvement in the watch and jewellery fields under our belts tend to assume that a familiarity with the different types and purities of gold is something that is automatically present in every newborn child, the fact is that a lot of the general public, quite reasonably, are not entirely sure as to what the different figures and associated karat grades actually mean. We are very keen to demystify all aspects of the collectible watch world and thought it was well worth while to take a few moments to compose something of a beginner’s guide to gold in order that even the complete novice with no prior experience can make an informed and educated decision as to whether he wants a vintage gold watch and, if he does, what karat grade he will find most suitable.

While this sounds like rather a bizarre statement of the obvious, the key thing to remember is that gold, in its pure form, is always the same. As a pure element, whether it comes from South Africa, India or even Wales, it is chemically identical. It has the same colour shade, weight and molecular composition.

So far so good. Why things become more interesting is that gold is rarely used in its pure form, but is instead blended with other metals to create an alloy. In its undiluted, pure state, gold is extremely soft and unsuited for applications where it will potentially be abraded. Alloying it in this way not only make it harder, but also makes a limited quantity of pure gold go much further in commercial terms, leading to increased profitability for jewellery and watch case makers. In fact, it is recorded that in 1854 when it first became legal to describe and sell alloy as gold that had a lower than 75% ( 18 karat) gold purity standard, this change was brought about due to pressure put on the British Government by the watch case manufacturing industry.

Things become slightly confusing because a whole variety of different alloys can legally be sold as “gold”. Two items, both clearly labelled as gold, can sit side by side for sale in a jeweller’s window yet in fact, one can contain a much greater percentage of pure gold in its alloy than the other. It is very important to realise that the term “gold” when used by the retail jewellery industry is very general and encompasses a wide range of alloys, and more information as to actual purity should be obtained before a purchase is made.

Clearly, in an environment where alloying in the norm and the generic sales term “gold” doesn’t tell us enough information in itself, an effective method of defining the percentage of pure gold in an item sold under the general term of gold is required. Worldwide, the pure gold content in an item coming under the wider heading of “gold” is defined by its karat and by a stamped indication of its pure gold content per 1000 parts.

The karat scale takes pure gold as 24 karat. The karat then reduces directly in proportion to the amount of pure gold present in an alloy. So, for example, 12 karat gold would contain 50% pure gold, alloyed with 50% other metal. In very basic summary then, the higher the karat, the more pure gold content is present and conversely, the lower karat, the less pure gold is in the blend.

The parts per thousand scale is a literal indication of the pure gold content present. This takes the form of three figures behind a decimal place. So if a watch case was in an alloy with a 50% pure gold content, which we’ve seen above would be 12 karat, it would contain 500 parts of pure gold per 1000 parts total. So its parts per thousand stamp would be .500. If it was 18 karat gold, as we know that 24 karat gold is pure “undiluted” gold, we could work out that it contained 75% pure gold and 25% other metal. So there would be 750 parts pure gold per 1000 parts total. Hence the parts per thousand stamp we find inside 18 karat watch cases is .750.

Theoretically, is would be possible to create “gold” of any karat and part per thousand figure simply by altering the ratio of pure gold to other metal when creating an alloy. So, hypothetically speaking, there would be nothing to stop us even creating bars of 1 karat gold or .042 by blending 4.2% pure gold with 95.8% other metal. In reality, though we’ve used this example to illustrate just how far things could theoretically be taken, British law states that anything with a pure gold content of less than 37.5% ( .375 parts per thousand or 9 karat gold) cannot legally be sold as “gold”.

It is hard to resist adding the note that it seems very bizarre that 9 karat can legally be sold as “gold” when we stop to consider than in fact, more than half of its content, 62.5% to be accurate, isn’t gold at all. It would seem logical that anything that isn’t at least 50% gold shouldn’t be described as such, but of course, we have no influence on the legislation behind these matters. I do know that if our business started offering vintage “Rolex” watches for sale that contained only 37.5% original Rolex components and 62.5% of parts by other, non-Rolex, makers, we’d end up behind prison bars very quickly !

Despite it being theoretically possible to blend gold alloy of any required purity, in practice there are certain standard purity grades that one encounters regularly as the norm. In truth, a familiarity with these is really all that is required in the vintage wristwatch world.

18 karat ( .750) contains 75% pure gold.
14 karat ( .585) contains 58.5% pure gold.
10 karat ( .417) contains 41.7% pure gold.
9 karat (.375) contains 37.5% pure gold.

18 and 9 karat are the two purity grades almost always encountered in the cases of vintage gold watches that were sold new in the UK. 14 and 10 karat cases were typically used for vintage gold watches sold in the American market, though the former occasionally crop up on models intended for sale in mainland Europe, usually with accompanying Swiss hallmarks. Just very occasionally, we have unearthed very early, World War I era, ladies’ vintage Rolex models with 12 or 15 karat gold cases, but these are so few and far between as to hardly merit mentioning. 12 and 15 karat gold was popular for jewellery in the Victorian and Edwardian eras, but even by the outbreak of the Great War this was unusual and from 1932 onwards, these two karat standards were no longer stamped at British assay offices.

The commercial worth of gold as an alloy is entirely defined by amount of pure gold in its makeup. So, for instance, 18 karat gold with always be worth twice that of 9 karat gold, simply because there is twice as much pure gold contained in it.

Having said this, it is important to appreciate that this correlation between gold purity and monetary value applies only to gold as a metal in isolation. It does not apply to watch cases or complete watches, because many other factors then come into play. Fashion, visual appeal and rarity all are very important in defining value. An 18 karat vintage gold watch will almost always be worth significantly more than the same model in lesser 9 karat gold, but it would be pure luck if this enhanced value was exactly double. It may be more than double or it may be less, but we cannot work out the market worth of vintage wristwatches simply by looking at the gold content in their cases. Ironically, there are actually many instances when stainless steel examples will be worth many times that of the same model in 18 karat gold; Patek-Philippe chronographs from the 1940s being a classic example to mention, because very few of certain model references were ever manufactured in steel in the first instance. Gold content plays an important role in defining value, but it can be trumped by both rarity and market taste.

Another subject worth briefly discussing is gold colour. We’ve seen above how the gold used for watch cases isn’t actually pure gold, but is in fact an alloy consisting of some pure gold blended with other metal. The choice of this other metal, or metals, will have a great bearing on the colour of the resulting gold alloy. Pink gold, also correctly known as red gold, is created by increasing the copper content in the alloy. Lower karat white gold contains a high percentage of silver, but interestingly, when 18 karat white gold is found, the silver is largely substituted for nickel or palladium. Years ago now, back in the late 1980s, we bought the most wonderful art deco vintage IWC from the 1930s with a rectangular stepped case in the most vivid green gold imaginable. We didn’t know it at the time, but in fact, the 18 karat gold used for this case must have contained a substantial amount of silver and cadmium to give it this bright green hue. It goes without saying that whatever colour it is, gold alloy of a specified grade, be it 9, 14 or 18 karat, contains the same percentage of pure gold. So, for example, 9 karat pink gold has just as much, 37.5%, pure gold in it as 9 karat white gold, 9 karat yellow gold or any other colour of 9 karat gold you might care to mention, and the same point applies to all the other karat grades also.

A final note that doesn’t actually affect anyone’s understanding of the subject is to note that in the context of gold purity, karat, as it’s spelt in this article, can also be written as carat. Both spellings are correct and entirely interchangeable when discussing gold, but when used to define the weight of gemstones, then carat must always be used. We can’t honestly say why we have always used the karat version for gold since the year dot in our business, but suspect that we originally may have felt that keeping one spelling exclusive to gold and the other for diamonds helped to eliminate the possibility of any confusion.