Dear Tan, a separate note about the tarnish on platinum. This
one puzzles me because the platinum I use doesn’t tarnish. Then I
remembered you mentioned your jewellery repair activities.
Perhaps the tarnish you are seeing is rhodium plating which will
burn and discolour if it is not protected with boracic and
metho’. Even when it is protected rhodium plating will
occasionally discolour, and the only way I know to remove it is
the hard way - meticulously emery it off the surface where you
can, and repolish. This may sound slack to the more meticulous
jewellers out there, but I hardly ever rhodium plate over
platinum. I like platinum the way it is, and I prefer to choose my
platinum solders carefully so that they are as close to the
platinum colour as possible so I don’t have to worry about
plating. I insist on doing any repairs and alterations on my own
pieces that might be necessary, so I know where all my solder
joins are, anyway. Frankly, I hated doing repairs on other
people’s work when I had to, and now refuse to repair or alter
anything I haven’t made for the very reason that I was always
coming undone because of unexpected solder joins in unexpected
places that were often hidden under the ubiquitous rhodium! Whew!
got that off my chest, didn’t I? Hope this helps, Tan, and good
luck. kind regards, Rex from Oz
Rhodium plating will burn off soldering on simple 14k gold, If
you are trying to solder or heat platinum no matter what you
will burn off the plating. It could be an oxide from the rhodium
that’s left but if it’s not and your getting tarnishing on
platinum, it aint platinum! Might want to get more info on what
your working with. then again I could be wrong. But…
Matt the Catt
i’ve missed a lot of this thread, but it seems that we’ve
experienced an oxide on platinum while heating it? could be the
alloy…plat / iridium and plat / ruthenium will retain their
beautiful polish even when heated to welding temperature, but
plat / cobalt will not. although this alloy is more commonly
used in Germany, i do find it occasionally here. i use it
often, when i want a hard platinum alloy, but it’s harder to
polish and to set into. when you heat it, it will oxidize to a
gray color. it will also work harden faster than the other
alloys, so i use it for die forming and anticlastic
forms…thin but strong and hard.
zaruba
Hi all,
In reply to the tarnishing of the platinum piece of
jewelry.There could be a couple of reasons as to why this is
happening. Firstly from the casting side of things, if the caster
uses an induction method of casting and is using crucibles with a
high silica content then an oxidation atmosphere must be
introduced to avoid the reduction of silica from the crucible
therefore contaminating the platinum. Secondly is bench
cleanliness. Platinum has a thermoelectric attraction to other
metals such as iron, silicon and manganese which may diffuse
into the metal if a reducing flame is used. After working the
platinum be sure to before annealing to pickle the piece in hot
hydrochloric acid to remove whatever iron may have combined with
it from the tools used. Regards. Neil George.