I am a professional design polisher & split lapper of fine jewelry.
I have requests for Rhodium plating on most of the gold & platinum
work that I do for customers. I have very white Rhodium, but lately
I find that the whiteness is not consistant. I have been doing
nothing different. (I am using electocleaner, acid bath and all of
the rinses suggested).
I make sure that my Rhodium is:
a) covered, so no dust gets into it.
b) charcoal filter it on a regular basis
c) only add distilled water to it when needed
d) add more Rhodium when needed
Could the problem be that the pieces of jewelry that I do are not of
a consistant in size?
Should Rhodium be heated up at times or kept at room temperature? ( I
keep mine at room temperature, but sometimes I heat it up to give it
a boost, & then I change my bath)
How often should I be changing the bath? ( I have a quart bath size
and I use 2 Platinum anoids) I do large quantities of plating, and
change the bath regularly, but how often is suggested?
Any tips, suggestions, or help would be greatly appreciated.
victor - as a not usually suspicious person it nonetheless tweaked my
suspicions: with rhodium currently above the $2,300 level & with
previous prices always the most costly of the metals, could it be a
tad weaker than your old because of slight dilution? which of course
introduces all sorts of other properties with any diluting agent
thrown in. ive
I have very white Rhodium, but lately I find that the
whiteness is not consistant. I have been doing nothing different.
(I am using electocleaner, acid bath and all of the rinses
suggested).
Hi Victor,
I find this interesting as I had a supply of Rhodium concentrate that
I used to mix myself with a 2% solution of sulphuric acid. In all the
years I have been working I have never had any problems. Bright and
white. Then I bought some new solution from the same supplier (Johnson
Matthey here in NZ ) but they only do pre-mixed now. It seems much
weaker and although bright it has a slight greyness to it. This really
shows up when you have any pave set areas. One of our last minute jobs
at Christmas was a large domed white gold ring with just under 2ct of
diamonds pave set. Although the rhodium was acceptable, I wasn’t very
happy with it. It still had a certain greyness about it. I am forever
renewing the solution unlike the old solution that would last for
ages. The only thing I can put down to is the weaker solution. I am
even thinking of importing some to try and solve this as I am pulling
my hair out over it something I can,t afford to do grin ). So if you
are buying pre-mixed may be you should try and find a supplier who
still sells the concentrate. If my memory serves me right it came in
2grm concentrate. If you solve your problem may be you could let me
know how you did it.
I am having some trouble with our rhodium solution. I know this was a
thread not too long ago but I must bring it up again. I have been
rhodium plating white gold jewelry for 20 years. I have always
purchased our solution from Hoover. In all that time I have had
little no trouble getting a beautiful bright finish our white gold
jewelry. That is until the last year or so. In that time, after only
two or three weeks of use, we get a dark or dark and spotty look
after rhodium plating. We have to replace the solution to remedy the
problem. In the old days we could use the same solution much longer.
Here are some details; We rhodium plate 50 to 100 rings per week. We
dip the item to be plated in distilled water before it goes into the
rhodium. We keep the distilled water and the rhodium covered when not
in use. We use a pure platinum anode and wires to hold the work. We
filter the solution and add distilled water that has evaporated
regularly. We plate at 3.5 volts. We are very careful not to
contaminate the solution. So what is wrong! It seems that for years
we could abuse the solution with no adverse results, now it seems to
have become so delicate. I wondered if the solution was now weaker
than it used to be. I just don’t know, and I am sick of buying so
much rhodium. The one thing I haven’t used is a replenisher, that
might help. But we never used it in the past. Please help. Thanks
Mark
Hi Mark; I’ve been lurking for a few months now but something in your
letter really caught my eye.you say you’re filtering the solution.I’m
not sure of the process your using but that could be where your
rhodium is being depleted.I’m not an expert on plating ,and I only use
a pen in my shop.I was always trying to be perfectly clean and use
only distilled water when I first started with the pen and wasn’t
having very good results.Then I saw a friend abusing his pen with a
dirty tip ,using tap water and getting great results so I’ve since
changed my attitude slightly.perhaps you’re being too
careful as well.I hope you find the source of your problems.Dave
Tom, we did rhodium plate at 6 volts for years but noticed the
manufacturer recommended 4 volts. So we adjusted the voltage. I had
hired a couple of old dog goldsmiths and they both thought 6 was too
high. What changed my mind was frequent dark spots at the contact
point, where the wire hit the shank, we determined that was from
sparking that was related to the voltage being a bit high. Anyway the
lower voltage eliminated that problem. Have you noticed the
life of your solution is not what it used to be? Mark
...you say you're filtering the solution.I'm not sure of the
process your using but that could be where your rhodium is being
depleted
Not unless the filter is some highly unusual material capable of
filtering out DISSOLVED rhodium salts. Not likely. I used ordinary
coffee filters for years with somewhat abused rhodium solution.
Careless use would end up leaving various forms of dirt and sediment
in the solution, which sometimes gave spotty deposits. We’d filter
the solution to remove the sediment, and it would then work better.
No harm to the solution. On the other hand, if the filters used are
contaminated with various organic solvents, or other dissolvable
organic compounds, THAT might contaminate a plating solution easily.
And of course, rhodium solutions don’t have great amounts of rhodium.
They DO get depleted in time, since the anodes used do not replace the
rhodium plated out. Thus you need, periodically, to add rhodium
replenisher solution. The color of the bath is a good guide. Keep a
small sample of the original new solution in a sealed clear bottle for
reference. As the solution gets used, it’s color gets lighter. when
the deposit starts to get spotty or otherwise poor, add replenisher
solution until the color is as dark as the original. Also note that
certain metals should not go in a rhodium bath. Silver, in
particular, can contaminate the bath, giving spotty or dark deposits.
That one is hard to fix. Also, as the bath gets used, over time, some
acid may be lost or neutralized by various means. If the ph of the
bath becomes sufficiently less acid, it will then no longer perform
correctly. Sometimes, adding a small amount of sulphuric acid will
correct a badly performing rhodium bath. The desired ph of rhodium
baths varies with the manufacturer, so I can’t give you a precise
desired measurement. But you can get small test strips that will
measure the ph in these values, accurately enough for routine
maintenance (though a ph meter is better). Measure the ph of a new
bath and record that on your little test bottle too. Then you can
compare as needed.
Dave, You may be right, that abused rhodium is better. I am not sure
about the filtering being the culprit. You see we fill a glass beaker
with fresh rhodium and mark the level on the outside of the beaker.
After a week or so, some of the water has evaporated from the
solution and the results are getting a bit spotty. We will filter the
solution through a coffee filter and add distilled water to bring the
level back up to the mark on the beaker. This removes any crud that
might be in the solution and perks it up to give good results again.
So I don’t think that is depleting the rhodium, but maybe
it is. Mark
It is also a good idea to carbon filter your rhodium solution if you
are having a problem. Add some carbon powder on top of your filter
and poor your solution through the carbon… this should remove
impurities in the solution. Daniel Grandi
I have used the same rhodium solution in a mason jar for two years and
get excellent results. It has a fine layer of mystry “crud” material
at the bottom and the solution has never had any water added. It is
always kept capped so evaporation is minimal. As I said
two years and counting and it still has great results.
Another problem to consider with any plating solution is what is
known as “drag out”. As you take a piece out of the solution a small
amount of rhodium is stuck onto the piece. Over time, especially if
you are doing a lot of plating, a significant amount of solution is
lost. If you think that you are just losing solution through
evaporation and fill the solution up with water, you are, over time,
reducing the strength of the plating bath. This is why it is
necessary to use replenishing solution.
Hi Larry, You are dead on about drag out being a problem for rhodium
loss. My step- father was a polisher for the trade in Los Angeles.
Immediately after rhodium plating, he rinsed the piece in a container
of distilled water he kepted just for this. Eventually, the distilled
water took on the color of the rhodium; or almost. It was then poured
into the rhodium and the process was began all over. Have fun. Tom Arnold
It is also a good idea to carbon filter your rhodium solution if
you are having a problem. Add some carbon powder on top of your
filter and poor your solution through the carbon.... this should
remove impurities in the solution.
An addition to that comment… what works best for me is ACTIVATED
carbon/charcoal. Easiest place to get small amounts of it is at any
pet store that carries aquarium supplies. This is the same filter
carbon used in the various types of water filters for aquariums. You
can either get it in bags with significant amounts, or just buy a
couple small “snap on” filters of the type that fit over undergravel
filter tubes. Break em open for the carbon granules or powder if you
want it seperate from the plastic cartrige… Do note that this stuff
works partly because it’s porous, and it will soak up and retain a
small amount of the expensive rhodium solution as well as helping to
remove organic contaminants. It’s not much, but the implication is
that it’s best not to use enormous amounts of the carbon, or you’ll be
throwing away some of your costly solution in the carbon…
Peter mentioned that activated carbon would be better and he is
correct. I would suggest that you put the powder on your filter and
pour your rhodium through the powder on the filter. After you are
done, take a small water spray bottle filled with distilled water and
rinse the remaining rhodium on the filter back into your beaker.
This will take care of any possible liquid evaporation your solution
may have had over time.I also recomend using the same spray bottle to
rinse the rhodium off of the item when you are done plating back into
the beaker.Using this method, your solutions life will be greatly
extended Daniel Grandi
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