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Rodium plating is coming out to dark


#1

A client is having a number of different issues with his rhodium
plating system. Mostly the finished product is coming out to dark!
They are using a console system sold by Gesswein Inc. it has three
stations. They have been instructed to “Not heat the rhodium” by the
tech department there. They use the electro clean(+rinse), and acid
activator(+rinse), as well as a palladium plate before the Rhodium
plate. Still with poor results. They have filtered and re-filtered
the solution. I have heard from a local jeweler, that he uses borax
to clean the solution? Apparently he sprinkles some into the
solution and stirs/dissolves it (it eventually settles to the bottom)
They have taken identical pieces to him and his rhodium comes out
perfect bright white. They have tried everything at this point except
a new / fresh rhodium solution. They have ordered solution from Rio
Grande and are waiting its arrival.

After being directed by different suppliers to use different
techniques there doesn’t seem to be a clear path.

If anyone has any suggestions, or directions, or secrets it would be
greatly appreciate it.

Thank you


#2
If anyone has any suggestions, or directions, or secrets it would
be greatly appreciate it. 

Borax? Unless there’s some bit of chemistry I’m missing, I can’t
imagine how that would help. Rhodium solution is sulphuric acid
based, and borax is a base, which would neutralize some of the acid.
But it’s more common for Rhodium solution that’s been in use a while,
to have too little acid, as some of it degrades over time So larger
platers routinely check the ph of their baths, and adjust, adding
acid if needed. Rarely, one might need to raise the ph, but again, I
doubt borax would be the recommended way (but I could be wrong on
that)

What might well help is to filter the solution. Rhodium can be
contaminated by a number of unfortunate impurities. You can get some
of them (mainly the various organic compounds) out of it be filtering
the solution. Put some “fish tank” activated charcoal in a coffee
filter, in a suitable funnel or other holding container, and allow
the rhodium solution to percolate through the charcoal. In many
cases, this can cure or at least help an otherwise messed up bath.

Be sure your various rinse solutions are distilled water, if you
live in an area with hard water. Even with good low hardness water,
it’s a good idea. Take care not to let the electroclean residue get
into the rhodium. It’s basic, and is one way the ph of the bath can
end up too high. The rinse you use after the rhodium will then
contain rhodium itself in small quantities. So that’s the liquid you
use to replenish any evaporation losses in the rhodium itself. That
way, your rhodium bath doesn’t get depleted by drag-out.

Try a lower voltage and a larger anode. Voltages/current density on
the low side sometimes can get a damaged rhodium bath to still work
acceptably, but too high voltages can darken the deposit with even
the best bath. And you almost always in plating, want the surface
area of the anode to be equal to, or larger than, the surface area of
the workpiece, in order that the workpiece surface area is the part
of the circuit that limits current flow, rather than the anode,
which can lead to indeterminate plating conditions at the workpiece
surface. Platinum or platinized titanium are the two anode materials
you normally can use. don’t use things like stainless steel, or other
metals, unless the bath is specifically designed for such an anode
(most aren’t) And agitate the workpiece a bit during the plating
operation.

Your source is correct in that rhodium solutions generally are
intended to be used at room temperature. The same is not true of the
electroclean. It works a lot better steaming hot, and at a
sufficiently high voltage/amperage/current density so you get
vigorous bubbling action. Be sure it’s mixed to the proper
concentration if you buy it as a powder rather than premixed
solution.

I’m also curious about the palladium underplate. In our
manufacturing, we make part of our line in a 950 palladium, and have
found it does not rhodium plate well at all. The rhodium bath leaves
the palladium castings with a worse (dull/matte) polish than they had
going in, and a color that is not an improvement over the palladium
itself. Palladium is indeed used as an underplate for some things,
but have your client check to be sure it is appropriate as an
underplate for both the specific rhodium bath used, and on the types
of metals he’s plating. I would not be surprised if there is a
mismatch there that might cause at least some of the problem. What
kinds of metal is he plating? White golds need no underplate at all.
(Neither do yellow golds, if you happen to be rhodium plating
that…) The rhodium can go right over the gold. With silver, the
traditional underplate sequence is first, a copper flash, and then,
bright nickle over the copper (the copper color makes it easy to see
when you have complete coverage with the nickle, and the nickle
adheres better to the copper than it does to silver directly.) Now, I
can imagine the desirablity of using something other than nickle as
an underplate on silver, if one wishes to avoid nickle in the
product. But be sure that both the palladium bath, and the rhodium
bath, are compatible with each other.

Hope something in there helps.
Peter Rowe


#3

First, make sure the item being plated is as clean as possible.
After ultrasonic and steamer, Electro clean it and rinse it in
distilled water. City water has chlorine which will affect the out
come. Make sure the volts and amps aren’t too high. Sounds like this
could be the problem.

Here is a link with very good guidelines for all plating needs. If
you buddy follows these instructions, he should have no problems.

http://www.shorinternational.com/PlatingInstrGen.htm

Best of luck, Steve
Arista Designs


#4

When I first started rhodium plating I had the mistaken belief that
I should reverse the wires (+ & -) as is done in stripping when
electrocleaning.

It made more sense to me than “plating” with the electrocleaner.
Many pieces came out too dark. I was told by the friendly folks at
Stuller bench that I was doing it backasswards.

Now everything is perfect.

Oh and I use the products Stuller sells: The allegedly earth
friendly powdered electroclean, some stuff called activator.


I use the cleaner at too hot (I usually forget it’s on the fire and
it boils) and I only use distilled water to rinse.

Fresh distilled water between solutions and I rinse multiple times.
(I use 30ml Pyrex beakers for the rinse & dump the used distilled
rinse water down the drain. Keeps the earth on its toes.)

The activator and the rhodium plating solution are both used at room
temperature and I electroclean and plate at 4 volts.

Oh and I rinse the rhodium solution off in a solution of baking soda
and water. When it gets too yellow I give it back to Mother Earth
from whence it came (more or less.)

I don’t work for Stuller, blah, blah, blah.


#5

Try removing the palladium bath, heating the rhodium to 110, and
rinsing in distilled water between steps. I start with a tivaclean
solution at 160 degrees first, using a stainless steel anode. You
better have a plating hood to suck away the fumes.

Peter B. Wolff
Gold Wolff Jewelers


#6

One thing to check is electrocleaner temperature. I’ve found that
once overheated its best to discard and make a new batch. Typically I
use it now at a cooler than recommended temp, still works well, I use
the calibrated hand technique, if it doesn’t hurt its OK, if its
steaming like spaghetti water its way too hot. Sometimes the lead
wire can make a diff. Too small and it doesn’t conduct enough. Don’t
agitate too vigorously, can cause sparking and pits.

Never put bare silver in.