G'day Lyn; There are several things you can use.
- If the gold is below 18 carat - contains copper - then you can
immerse it in 'liver of sulphur solution', or 'lime sulphur' from
gardening shops which will blacken the whole ring. The blackening is
easily polished off in places where you don't want it. If the gold is
18 carat or higher, then you will need to copper plate
it first by immersing it in used pickle together with a bit of iron,
then immerse in the sulphide solution. Polish off. Fine gold (the
pure metal) does not react with many chemicals other than aqua regia
which dissolves it. Which is why gold is found as the metal
(alloyed with other metals) and not as an ore.
2.Paint the engraving with good quality black enamel paint, allow to
harden thoroughly then sand and polish off.
3.Coat the engraving with mixed 2 part epoxy resin coloured with
black or other colour of powder paint medium, sand and polish off.
Heat the item and flow niello into the engraving. Sand when cool
and polish off.
Paint the item with gunmakers black and polish off.
The most durable of all these is niello; (difficult to get) next in
line is the epoxy resin.
Cheers for now,
John Burgess; @John_Burgess2 of Mapua Nelson NZ