Understanding P531 Gold Hallmarks: Is It 13.5K?

Question
Hello,
I recently purchased a ring from a local antique store whom purchased the ring through an estate auction.  Its band is a very soft (light)yellow gold color. It has a hallmark of P531.  I have looked up as much as I could find, and all I can find is what 12kt and 14kt numbers are in European hallmarks.  So, if this is an European hallmark, than it seems it would be about 13.5 part gold, but I can't seem to find anything that states there is such a gold combination.  I have also seen the letter markings stating the years in could have possibly been made in, but the "P" text does not seem to match any that I found.  The "P" is also not enclosed in a box.  Any help would be so appreciated.  
Thank You!

Answer
G'day Amy and many thanks for your query.

The International (not just European) marks are a measure of purity in metals, stated in decimals by 'Parts-per-thousand'. Even the USA uses them now - but it's NOT compulsory.

This means if the mark is 375 - it shows there are 375 parts of pure gold mixed with 625 parts of other metals to produce 9kt gold. There is NO decimal measure for 531.

14kt is 585 for example or .925 is Sterling Silver.

It sound like this item is simply stamped with a Makers design or identification mark. The P531 could be a model design and nothing to do with a hallmark at all?

You say there are date letter marks. Do you mean other marks or are you just thinking the 'P' means a date letter?

The 'P' would be more in tune with Platinum, but as I cannot see it, feel it, measure or test it, you are going to have to get your local FRIENDLY jeweler/ appraiser to take a look at it. Get a written report. They will charge you for this, but at least then you'll know for sure, otherwise you are just guessing.

There is also a free Hallmarking course here which you might like to read. It covers British Hallmarks.
http://www.online-jewelry-appraisals.com/free-hallmark-course/

You might also like to add this query to my blog at http://how2valuejewelry.com/ as other may have had a similar problem. Can't hurt anyway and who knows what answers you may get.

Hope this helps...