Jewelry, Gems, & Minerals/question about ring
Joanne wrote at 2014-06-01 17:11:51
The 1/20 PT marking most likely means that the ring is coated with a layer of platinum (which is what PT stands for) that is equal to 1/20th of the total amount of metal (silver in this case). Coating sterling silver jewelry in platinum is a very common practice for many reasons ... There are quite a few people who are sensitive to 925 sterling silver; its typically not the silver that they are reacting to but the other metals that are mixed in with it. The 925 marking means that you are getting 92.5% pure silver mixed with other metals to create a more durable piece of jewelry, pure silver [marked as 999] is too soft for use in jewelry. Copper is the industry standard for mixing with silver, so much of the 925 sterling silver on the market is actually 92.5% silver and 7.5% copper, but there are other metals that can be used as well. Nickel is one that isn't used very often, except in cheaper costume silvertone jewelry, as it is known to irritate the skin of many people, which is why you'll see "Nickel-Free" so often on any silver colored jewelry. Platinum, on the other hand, is one of the most hypoallergenic metals out there - VERY few people have issues with platinum and when you have a piece of jewelry that is coated in platinum, platinum is the only metal that actually comes in contact with the skin so it is an excellent choice for people with sensitive skin, or really for anyone. The only thing better than platinum, in terms of sensitivity and hypoallergenic-ness is surgical grade stainless steel (which is relatively very low in price, will never tarnish, looks just as good as any other white metal out there, and is by far the best choice for piercing). Platinum is also one of the highest quality and most expensive metals used in jewelry making and is typically what the VERY nicest gemstones tend to be set in nowadays. Therefore, choosing sterling silver jewelry with a platinum overlay is an excellent way to get all of the benefits of platinum at a fraction of the price. The industry standard for the amount of platinum coating on a piece of sterling silver jewelry is 1 micron (but the more the better, good jewelers use about 4 microns to ensure that the platinum coating is there for good). Typically only a fine jeweler would have that kind of information, however the 1/20 marking on your piece sounds to me like it's been coated with 1 micron, and although that is speculation, having that marking does give you a way to find out, if you are so inclined.
Additionally, in my google search to confirm all of this information, I saw some mention of rings that have a marking of or like 1/20 which is said to be the carat weight of the gemstone in the ring. I suppose 1/20 would mean that this particular ring has a 1.20 carat gemstone, but this seems like an odd way of marking carat weight plus it is very very rare that the band is ever marked with information about the gemstone that is set into it (I've NEVER seen it or even heard of it until this google search), because unless it is artisan-made, the rings (all jewelry settings really) tend to be made by a different person than the one who sets the gemstones. There are a lot of specialities in the jewelry trade and the master silversmith who creates the beautiful settings is not always the best person to work with gemstones. Anyway, I think that this being attributed to the carat weight is just a mistake (obviously not everything you read on the Internet is correct) and I'm sure that you know the carat weight already so you will probably be able to rule that out yourself immediately.
I hope that this was helpful.