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Plated sterling, the plate "bubbles" under heat


#1

Dear Jewelers, etc., There is a plating used on sterling with the
appearance of sterling in color, not the harsh rhodium look. This
plate has been around a few years now. When soldering is attempted,
the plate forms “bubbles” and refinishing to the surface metal is
needed for even a “half decent” look. There appears to be nickel and
or copper underneath. If you have encountered this, you know exactly
the plated surface in reference. On new items, the plate is
difficult to recognize. Yet, worn items do show characteristics
"edges" of wear. Also, in a well used pickle, the plate causes copper
deposition on the item.

My question to anyone who knows it this: What is this plating? What
is the metal?

Thanks for any replies.
Thomas Haynes


#2

My question to anyone who knows it this: What is this plating? What
is the metal?

You sure it’s not rhodium? Over sterling, it’s usually got first a
copper, then a nickle underplate if it’s done correctly. and the
surface color isn’t always so harsh either. Rhodium behaves exactly
as you describe, and so far as I know, is by far the most common
plated finish on sterling. I say that simply because there may be
others I don’t know about. Every bit of plated sterling I’ve ever
seen is a rhodium finish. Like I said, there may be others I
haven’t seen or recognized as such… But I do know rhodium isn’t
always so harsh. As with any plated finish, it’s surface depends
much on the condition of the underlying surface, and with a new bath
working right, it’s color can be quite bright and white, and not
always obviously different from well polished sterling unless you’ve
got a comparison piece right there… One easy test is to try
polishing it. rhodium is hard enought that with normal polishing
compounds, it’s very slow and difficult to polish off (use platinum
polishing compounds, such as sold by Gesswein, which are based on
Aluminum Oxides. These take off rhodium just fine) Most of the
other metals you might plate, while likely to produce a plated
surface that’s harder than sterling, would still be softer than
rhodium, especially after you’ve heated the piece enough to blister
it.

Peter Rowe


#3

Hi , This is a pure silver plate… very thin as far as plating
goes… In this particular case, as in many cases, it has been
copper and nickle plated…The reason for this is to hide defects
in these particular castings… The reason I say this is the
following. If the item was plated to only give a bright silver look,
it would not be neccessary to copper/nickle plate the item … some
people like this color as it does not oxydize as easily…l

However… when it has been copper/ nickle plated before hand, this
is done usually to hide manufacturing defects in the item… This is
becoming common as many of the larger production houses are having
serious problems getting good castings in sterling. If the plating
were fully removed and the silver where polished,some of the signs to
look for would be grey spotting ( not pits) another sign is kind of a
dark crackly look . this would appear in the highly polished smooth
surfaces of the item. It will not come out , no matter how hard you
polish it. This surface problem is associated with casting deox
metals at the wrong temperature. Plating a silver piece this way
would also hide firescale from normal silver. If these problems were
apparent in the underlying metal, using a silver plate will not hide
the defects however, copper plating is used to smooth defects ,
Nickle is used as a barier plate to stop the copper from leaching
through. There are other explanations, but this is the general
reasoning. I feel that this is cheating and should not be done .
another reason I don’t approve is that the copper and nickle would
actually change the sterling content if it were fire assayed.

Daniel Grandi We do casting, finishing, assembly soldering, model
work, cnc, and a whole lot more


#4

Hello Thomas! I couldn’t tell what kind of plating it is but I’m
quite sure that the metal underneath is base metal as I have
encountered the same problem with what I thought was a bronze
statuette earring. My girlfriend had bought a single earring to this
retailer (she said that it was the only left(?)) and she wanted to
have two, so I was on the way of making a mold out of it when
bubbles appeared on the surface during sprue base soldering. It
looked like lead or pewter, but I could only presume as bubbles
showed up under little heat.

Hope this little tip helps!
Benoit Hamel


#5
   My question to anyone who knows it this: What is this plating?
What is the metal? 
  You sure it's not rhodium?  Over sterling, it's usually got
first a copper, then a nickle underplate if it's done correctly. 
and the surface color isn't always so harsh either.  Rhodium
behaves exactly as you describe, and so far as I know, is by far
the most common plated finish on sterling.  I say that simply
because there may be others.." 

New Post: Dear Peter, perhaps more specific experience with this
unknown plating will clarify somewhat. First, the color is very,
very close to that of raw sterling although with a slightly "harder"
visual appearance. In many cases, as with curb chains, the chains
are not finely finished in the first place and the plating is
extremely difficult to recognize with the eye. Therein is the
problem. The effects of heat to the plate are discovered after it is
too late and the blisters have formed. (Possibly I will simply
reserve some used pickle for a quick dip to see if a copper deposit
forms as a warning indication!) Obviously, the plate is to prevent
tarnish, as is a standard rhodium finish plate. The reaction when
soldering is like a thief in the night, unwanted and unexpected.

Slightly worn items, such as a heavy chain or bracelet will show
some discoloration or darkening of metal where the plate has worn. I
do not think this plate is quite so hard as rhodium.

When heat is applied, the blisters form and these can be up to 1.5mm
across. Beneath that is a darker color, perhaps nickel and
sometimes a copper layer. The metal is deeply discolored, more
deeply than with heat effects to quality rhodium finishes. (I do not
accept rhodiumed sterling for work in the first place.) The bubbles
plate may be buffed down with bobbing compound and finished but the
discoloration and a telltale ring remains from where the blisters
were, an orange peel effect.

My recourse to being the item to consistent color is abrasives such
as medium Cratex or the new and wonderful silicon rubber based
wheels(so called medium grit) on the polishing lathe spindle. From
here, the sterling is exposed and all can be finished to similar
color. Of course, tarnish will occur there and the customer is
advised.

As you suggest, it might be rhodium of a lesser sort than the
quality I am used to. I simply do not know. I do know it is a real
mess to deal with. Thanks for you reply.

T. Haynes.


#6
           perhaps more specific experience with this unknown
plating will clarify somewhat.   First, the color is very, very
close to that of raw sterling although with a slightly "harder"
visual appearance. 

I’ll trust your statement, and that of others, that fine silver is
now a common such plating. The mere fact that it’s likely a
"brightened" plating might well explain the “harder” look all by
itself. Eletroplates often have a somewhat different look than the
same metal when prepared by usual means.

       In many cases, as with curb chains, the chains are not
finely finished in the first place and the plating is extremely
difficult to recognize with the eye. Therein is the problem. The
effects of heat to the plate are discovered after it is too late
and the blisters have formed. 

since the bubbles are most likely a function of the copper and
nickle underplates, rather than the outer silverplate, this would
account for my experiences with rhodium doing the same thing, as it’s
also applied over copper and nickel underplates when on sterling.

    (Possibly I will simply reserve some used pickle for a quick
dip to see if a copper deposit forms as a warning indication!) 

That would only work, I’d expect, if the nickle is chemically
available at the surface, meaning the silver layer is either too thin
or worn. If it was thicker, your pickle test might not detect it.
You might also want to experiment with some liver of sulphur or
similar silver oxidizer. These, while they may affect fine silver
some, do it markedly less than sterling, if even at all. And since a
bit of “tarnex” will take the mark back off, it would be easier to
remove your test than would a copper flashing. Just a thought…

 My recourse to being the item to consistent color is abrasives
such as medium Cratex or the new and wonderful silicon rubber based
wheels(so called medium grit) on the polishing lathe spindle. From
here, the sterling is exposed and all can be finished to similar
color.  Of course, tarnish will occur there and the customer is
advised. 

You may also find the 3M radial bristle disc products to be of
considerable use in this type of situation. They get into details
well, yet also are good at maintaining surface contours, meaning they
don’t buff off high spots as aggressively as do normal buffs or
rubber wheels. And the metal removal rate is very uniform and easily
controlled. Try them. You’ll like them.

Peter


#7

I haven’t been following this thread religiously, but I would like
to throw out an opinion. Back when I did a lot of repir work I
often came across silver jewelry that had this heavy electoplate
that did not take heat. I was curious as to what it was. Though I
never did an acid test to see if it would react as a platinum based
metal, I always assumed that to use such a heavy plating of rhodium
on an piece whose obvious intent was to hold down cost was
illogical. Equally illogical was the fact that to rhodium was an
extra and not neccesarily needed step that would again drive up the
cost.

My assumption was that it was a heavy nickel plating. Nickel has
always been an easy metal to blame things on, so it worked for me.
I have always found that rhodium burns off rather cleanly even
though it does require fairly high heat; it never bubbled. As well,
the feel of the plating on silver always had a very slick feel to it
when put to a sawblade; much more like nickel platings.

One question that came to my mind that I never tried to answer was
if chrome platings were actually nickel type platings? If so then
it makes sense to assume that these pieces were chrome plated.

Any comments?

Larry


#8

When confronted with a repair like this the best solution I have
found is to strip ALL the plating and then refinish. Around a 60%
sulphuric acid solution, 6 volts and lead CATHODE removes all the
plating. The resulting frosted white silver surface can then be
polished (maybe tumbled with steel first if needed). This sounds like
a lot of work (it is :slight_smile: but it’s usually faster and better than
trying to polish off the plating. The real trick is to recognize that
the piece is going to blister BEFORE starting and then selling the
customer an upgraded repair.

Jeff Demand
http://www.aztec-net.com/~jdemand