In the UK It is illegal to sell a piece of jewelry as silver, gold
or platinum without a hall mark. This consists of three marks.
Who made the article - the initials of the maker What the metal is,
and its purity - the fineness mark Where it was tested (Assayed) and
marked - the Assay Office mark.
The piece has to go out to the hall and they will place the quality
stamps on it. You may mark it beforehand with your own mark.
If it fails the hall's test they crush the article and return it to
you. It happens! Yu can't get away with flooded solder, they will not
mark mixed metals as mixed.
You need to talk to the hall beforehand so that they place the marks
where you want them. Sometimes they seem to go to extraordinary
lengths to put the marks exactly where they shouldn't be!
There are exceptions for very light pieces weigh less than 0.5 grams
in platinum, 1 gram in gold or 7.78 grams in silver.
I much prefer the adult sytem of the USA.
Gold and Stone