Only if you want to legitimately stamp that piece 18ct.
In Australia we have a voluntary standard, that I follow
religiously, and a certain organisation would love to see as a
Within the Australian standard of precious metal fineness, you can
only stamp an 18ct yellow gold ring 18ct if it is entirely made out
of 18ct, including the solder. There ae exceptions to the rule, but
this is generally the case.
The tricky part come in when you use white gold. In Australia our
yellow gold solders match the karat of the gold. This is not the
case for white gold solders (I’d be interested to see if this is the
case in other countries).
White gold solder comes in hard, medium and easy. The hard is 18ct,
the medium is 14ct, and the easy is 9ct. There is not 18ct medium, or
easy solder. There is no 14ct hard or easy, and there is no 9ct hard
or medium solder.
An excerpt from the standard :-
"Solders used in the manufacture of gold alloy articles shall not
contain less than the article itself except as follows :
(a) In the manufacture of white gold articles containing at least 750
parts per 1000 by mass of gold, the solder used shall not contain
less then 585 parts per 1000 by mass of gold."
What this means is that you cannot use easy solder to on an 18ct
ring and stamp it 18ct. Any repair work done on an 18ct ring, with
white gold easy solder, will render it 9ct, as you stamp the piece by
the lowest karat gold. Any repair work, or construction work must not
use white easy solder if you are using 18ct or 14ct.
This is the Australian voluntary standard, I think the American, and
British standards are very different.
Kindest regards Charles A.