Something is very strange here, Harold. Practically every source says
that coin silver is the predominant material for silver electrical
contacts. There is even an ASTM specification for it -- ASTM B617 -
98(2010) Standard Specification for Coin Silver Electrical Contact
Any tips for separating the silver from the sludge in photographic silver
reclamation systems that use steel wool? The silver dust ends up mixed
with iron and iron oxides and who knows what from the used fixer.
I have gotten a couple of brass surprises myself, trying to
silver-braze it with some old braze metal of unknown composition. It
worked a couple of times, and then I watched it turn into a bag of
oxide-covered molten brass a couple of other times.
I imaging it's disconcerting to discover that property when you're
trying to forge it.
The O/A method will work fine. Have someone poke the silver with a
screwdriver and it will fall off when you hit the proper temp. I
used to do it with all my contactor tips but with the price of gas it
just wasn't worth it anymore.
I have a 1948 Metals Handbook. Two pages of Coin Silver alloys, with
specific info on contact material, physical characteristics, and how the
metal is worked for contact applications. Two more pages of Silver alloys
for electrical contacts. Silver-Tungsten, Silver-Molybdenum, Silver-Nickel,
Silver-Graphite, Silver-Cadmium, Silver-CdO, Silver-Lead.
The latter seem to be powder metallurgy, sintering and heat treatments. With
paragraphs on specific applications. Eg. Silver-CdO used in WW2 warplane
gunnery switchgear. Charts of how electrical properties vary with alloy
content, etc. Some info on how some contact pairs used different materials
on each side to reduce arcing. Eg Silver-Nickel in one contact and
Silver-Graphite in the other. Seems like 1948 era materials engineering was
more sophisticated than the casual reader would have guessed.
Silver and iron won't alloy, so you can melt the sludge with soda ash and
borax. Pour to a cone mold to separate the resulting silver from the slag.
If there's sulfates present, a couple pieces of scrap iron (lengths of rebar
work fine) inserted will ensure that the sulfur liberates any silver that's
combined. In such a case, you'll get three layers in the cone mold, the
top one being slag, the second a sulfide layer, hopefully sulfur and iron,
and the bottom silver. The silver should be of good quality, but can be
parted in a silver cell to ensure purity.
Even heavy duty contacts? That's predominantly what I refined. From
switching gear, for instance, not small appliances. Traces of copper
report in the solution, but nowhere near enough to account for the color
you'd expect from coin silver. In fact, the small amount could easily be
determined to be from the solder used to mount the contact.
I have almost no experience with small contacts, so that makes me wonder if,
perhaps, that's the type that may be made of coin silver (90% silver, 10%
Some silver contacts are alloyed with cadmium. I did encounter a small lot
of those. Amazing how little silver they contained.
I suspected that was it, because you certainly know your precious
metals. Coin silver apparently is used for the ordinary types of
contacts, both for consumer and industrial applications, but a variety
of other alloys are used for very high-current or high-voltage
Some low-voltage applications that require the lowest resistance use
fine silver, too.
Awesome tip. I've looked on photo forums and found nothing of value. The
dissolve the silver in acid and precipite it methods don't seem applicable
as iron will dissolve in those acids, and buying huge tanks of nitric
acid doesn't seem worth the effort considering the extra hazards.
I've been sending the used fixer to a lab with an electrolytic cell, so
they keep the silver, but it's more of a hassle for them once you factor
in transporting the stuff and returning the containers.
How much soda ash and borax should be used?
I did notice a hydrogen sulfide smell when steel wool is thrown into the
fixer tank. I'm not really clear on when it's ok to stop adding steel wool
as nobody has any idea how much silver is in the spent fix to start with.
One guide mentioned upto an ouce of silver per gallon. I suspect I need to
get some silver test strips to make sure the leftover liquids are safe
enough to dump. One doc says there can be upto an ounce of silver per
gallon of used fix, but until the silver is removed, I have no way to see
how accurate this is.
I know this is a very old thread, but all I did to remove my silver was take a
sharp chisel, a hammer, and a vise and the contacts just popped right off. I
had a wide variety of contacts, so some removed easier than others, but all of
them came off without too much trouble. Just make sure you use a chisel that
you don't care about.
Be careful, some of the older contacts had cadmium as part of the alloy. Most of
the refiners I talked to would not deal with them.I have several pounds of
contacts still attached to a small portion of brass. I would like to find some
one to buy them.