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Rhodium plated repairs and sizing


#1

We frequently run into this problem: sterling silver that has been
rhodium plated for repairs and sizing. The plating is not detectable
until we saw into the piece; then its hardness gives it away. We
need to know how to test for rhodium finished BEFORE we get involved
in soldering or brazing processes. Is there a way to test an item
for rhodium plating, rather than by its’ resistance to sawing and
high hardness?


#2
Is there a way to test an item for rhodium plating, rather than by
its' resistance to sawing and high hardness? 

This is totally not my area of expertise, but I can’t resist…

Put some Black Max on it!

I bought a beautiful sterling chain that I wanted to “antique”-- it
was WAY too shiny-- but found that nothing I did would change that
white gleam. QED

Noel


#3

Hey William

I have a lack of experience in this but is it the rhodium or the
nickle plate that is giving all of us trouble? I thought it was the
nickle plateing that made it hard. But on that line this is a good
question, when sizeing and soldering plated silver there tends to be
cracking and/or the plateing melting and bubbleing (with rhodium
being so high cost right now I think that it is a coating of some
sort that bubbles) any suggestions on how to avoid the named above
conditions? It looks like with the price of gold the bench will see
more and more silver, so I was hopeing to head the problem off at the
pass. Thanks for any

Happy Profits,
Sean


#4
Is there a way to test an item for rhodium plating, rather than by
its' resistance to sawing and high hardness? 

How 'bout silver testing acid?


#5

One cannot put silver items into a rhodium bath without destroying
the rhodium bath. One must nickel or copper plate first.


#6

Hi William and Sean,

I think the culprit is chrome plating. Rhodium is far too expensive
to use for brightening silver, and neither rhodium nor nickel are
particularily hard; they will bend and cut without much problem.

Chrome on the other hand is extremely hard and brittle; the saw
blade or file will skid on the surface and only cut with heavy
pressure. That is the surest test - try to file it with normal
pressure and the surface remains unmarked. Chrome plating will crack
with the slightest bending, revealing razor sharp edges that cannot
be removed. They can be dealt with by over-filling with silver solder
so that the edges are covered.

Basically, chrome plated silver is unworkable. Chrome is sometimes
used for cheap silver items because it is truly tarnish resistant.

Regards, Alastair


#7

Alistair:

I am not aware of silver jewelry being chrome-plated at all; it has
been traditional to plate nickel first, followed by rhodium,
although what you said about chrome is possible. The problem with
rhodium plating is that the plated metal has unusually hard
properties, much harder than the metal itself. This alone resists
sawing and filing like you said about chrome. The problem results in
the pickling, which will plate out copper from pickling solutions
unless they are brand new. Checking the standard electrode
potentials of rhodium vs. copper, it is not possible for the copper
to plate out on rhodium, but if the nickel is exposed, it is
possible. I see that there’s another thread dealing with this
problem, but just removing the copper plate is not enough. The
rhodium must first be removed by a bath of hot, concentrated
sulfuric acid, followed by a bath in hot hydrochloric acid to remove
the nickel underplating.

All of this is a major nuisance, and if the client wants it, the
rhodium finish must be restored after whatever sizing or soldering
processes are completed. The best possible proceedure is to identify
the rhodium plating in advance of any work, at least getting a
"head’s up" on whatever processes need to be followed. It is far
better to warn the customer in advance of charges involved with
plating removal and replacement; these fees can far exceed the value
of simple sizings or repairs, resulting in “sticker shock”. Also,
and soldering is far better accomplished if the rhodium and nickel
have been removed.

The first response to this topic was the best: test for silver. This
means that a drop of dilute nitric acid will react (or “fizz”) when
applied to a non-plated item; in contrast, rhodium will not react in
dilute nitric, revealing the true content of the metal. Thanks for
the advice!

William C. van Laer
ASTERISM Services
Butte, Montana


#8

oh how I hate bumper chrome as we call it, it is a layer of copper
then nickel, the copper bubbles and causes a big mess, most silver
you can scratch with you finger, at least mine callused, and the saw
will slide acroos the finish. if you have access to a laser you can
minamize damage, and in most cases it is not an option to take the
plating off, and when you do say an end cap on a chain and remove all
of the plating it will discolor sooner than the rest of the piece.
and in the long run, the plated silver turns dull grey and does not
clean very well. I wish they would stop using it

ringdoc