I am looking for points on removing all traces of lead and white
gold from a platinum piece I will be restoring on the laser.
Any suggestions??
The standard practice for removing unwanted metals from old repairs
in platinum restoration work is to immerse the piece in aqua regia
(a mixture of nitric and hydrochloric acids) until all traces of
foreign metal are removed. Using one acid or the other alone doesn’t
work well but the mixture does the trick. Don’t know why, maybe one
of our chemists can explain. I’ve always wondered.
Aqua regia will dissolve many platinum solders too, so be aware that
original fabrication work done using some of the older low-temp
gold-bearing alloys may un-fabricate, or become significantly
weakened. Sometimes you end up with a bunch of little pieces in the
bottom of the beaker and a whole lot more restoration work than you
bargained for.
There are many safety and environmental hazards involved with the
mixing, use and disposal of aqua regia. Check with your acid
supplier (the place you get industrial chemicals, not the guy down
the street with the pony tail and black light posters) for details.
Joking aside, aqua regia is potent stuff. Approach its use with
extreme caution.
The only other method I know of is physically removing the offending
metals with files, burs and gravers, but that won’t get rid of all
of it. Using that method, assume it is still contaminated with other
metals and proceed cautiously.
Dave Phelps
precisionplatinumjewelry.com
For lead use nitric acid if you have some handy. If not or if you’d
rather not screw around with acid you can remove both the lead and
the WG mechanically. (I hate working with acid, no matter how
careful I am my fingers itch, such a sensitive human being)
First you have to identify just where the goop is. For the lead, if
its an older repair, you should be able to see it, dull grey Grind
it, sand it, polish it, whatever you like, just avoid breathing it.
To check if you got complete removal just heat the piece up to lead
solder temp. It’ll get shiny for a minute. Grind some more if needed.
For the WG, heat it also, but just enough for it to discolor, then
grind it, whatever.
It might not be a bad idea…before you do the actual laser welding,
go low on power and a wide aperture and just go over the areas in
question. It should show any minute residual goop but shouldn’t
materially effect the surface finish of the Plat.
Try boiling in Aqua Regia.
This is a “Don’t Try This At Home Kids” technique. Very dangerous,
but effective. If the platinum piece is soldered together, beware,it
will also remove platinum solder too.
Good luck.
Jo Haemer
www.timothywgreen.com