I had used Platinum easy solder sourced through Cooksons in the
UK......and now I wonder how much platinum was actually in the
solder.
Traditional platinum solders such as you were using contain little,
if any, platinum. An easy grade will be mostly palladium and silver,
plus perhaps other metals. If there’s enough silver there, it will
etch, as you found. Also, the lower the melting point, the weaker the
joint. An easy platinum solder like that penetrates the platinum very
little. I like to think of it as a solder seam with about the same
structure as lead solder on gold, ie different metals wetting the
surface but not really penetrating or alloying with the native
metal. I’ve found I can solder a platinum wire down to platinum sheet
with, say, 1100 solder, and grab a protruding end of that wire with
round nose pliers and twisting the wire around the plier jaw, just
peel it off again like opening a sardine can. Might as well be just
glue, for all the better it holds. (yeah, I’m exaggerating a bit, but
it illustrates that these easier grades of solder should be reserved
for repair work only, in most cases, or places where durability is
not an issue.) Use the highest melting grade of solder you can manage.
I wouldn’t recommend using anything less than a 1300 solder for any
new construction, and most times you’ll be better off with a 1500 or
1600 grade, even for fairly delicate constructions. The 1300 grade,
by the way, still won’t have much platinum, and only marginally
acceptable strength. . 1500 has some, but until you get to the
“welding” grades, it’s still mostly palladium based alloys. And as
with much other jewelry making, the fit of the parts and seams has a
lot to do with strength. If the solder is filling big gaps with more
solder, it won’t look as good, and also won’t be as strong.
The plumb solders are vastly different. The “easy” grade is just as
strong as the harder grades. They can be slightly more brittle, but
not so much as to allow your pieces to come apart. Differences are in
color, melting point, and how easily it flows (the easy is more
sludgy and slower flowing, it seems, but nevertheless melts a bit
lower). All seem stronger than any of the “traditional” platinum
solders, in my experience. They ARE slightly more difficult to use
cleanly, as they don’t flow out quite as well. You get fine solder
flow, but the solder tends to leave a visible scar where you placed
the chip.
The stuff comes from “Precious Metals West”, in California. Find
their web site. No doubt you can order direct from them if you cannot
find a local supplier who carries it. As I said, it’s a little more
difficult to use sometimes, but the results are, with practice, far
superior to what you get with traditional platinum solders.
I obviously was wrong in using the nitric pickle at the point I
did, but after having iron contamination issues in the past I have
tended to err on what I thought was the safe side by making sure
there was no ferrous content on the metal surface before heating.
Use, rather than nitric, a hydrochloric acid based pickle. HCL
dissolves ferrous metals just as well as does nitric, but it doesn’t
etch the silver based alloys. And you shouldn’t need to pickle for
more than a few minutes at most. Even a standard sulphuric acid salt
pickle like sparex, if fresh, will remove ferrous contamination,
especially when coupled with an ultrasonic cleaner or steam cleaner
to help with any degreasing.
Hope that helps.
Peter Rowe