Resolving Tarnishing Issues Plating with Pink Golds
As a Rhodium and Gold plating solution manufacturer, we at Davis K
Products run into every type of Jewelry Plating issue. One of the
most common problems in gold plating is that of Tarnishing when
plating with PINK gold bath and pen solutions. The yellowing or
blackening or brown spot problem usually shows up minutes to hours
after manufacture, but can, in some cases, only show up after you
have delivered your work to the customer.
The most common versions of these products are the well known NON
Cyanide Pink, and the lesser known Cyanide based products. The common
Non Cyanide Pink is what most everyone uses, and is available
everywhere. It typically contains less gold, as the non cyanide base
simply won’t hold as much gold as cyanide, and the resellers to the
hobby industry tend to dilute these to the point where you can buy a
1 liter solution for very little money. Typically, the bath version
SHOULD contain 2 grams per liter, and should be labeled as such.
(Some are labeled in PWT: 1 PWT, or pennyweight = 1.555 grams) No
content label means not much gold. Pen solutions should contain 1/8
to 1/2 gram of gold, but most are diluted to far lower
concentrations.
The tarnishing issue with these solutions stems from the copper
content: it burns easily, reacts with oxygen easily, and can have a
galvanic with your base metals. Plating over “satinized” or
“roughened” surfaces is usually a guaranteed challenge. There
tarnishing can be coming from the surface, but not necessarily, in
many instances, an Anti Tarnish does not help the issue, this can be
due to the copper in the solution reacting with trapped acid from the
cleaning process, or with the base metal itself. Remember, gold flash
is very porous, and doesn’t stop your PINK from making contact with
the silver or other metal underneath.
Several of my customers who had excessive re-work using PINK golds
have found the following steps to be helpful:
-
Clean the hell out of your workpieces: - Ultrasonic, then
Electroclean at 6 volts for a full minute, then rinse WELL, in
multiple rinses. -
If you are plating over Silver and using acid activation, do small
batches, and make sure the acid is well rinsed off. -
If you are pen plating, use the lowest useful setting, the
operators won’t like it, (takes longer) but that can resolve a
“burning” issue. -
If plating over Satinized or Roughened surfaces, try plating with
Palladium first, its inexpensive, far less porous than gold, and
easy to apply. -
Try a higher concentration of gold in your PEN solution. The
diluted solutions have so little gold that the work is left very
porous. (Our cyanide Pink Pen has one full gram of gold in 33ml of
solution, for example, our Bath Pink has a full 2 grams/liter) -
If you are doing all of the above and still have Tarnishing
issues, switch to BATH, and mask of your parts with wax or stop off
or lacquer. -
In bath: Keep your temperature at the specified level, keep your
voltage down, make sure you have a GOOD, low ripple rectifier, and
aim for longer time, lower voltage where feasible. (an old rectifier
can make a lot of difference… and a good digital plating rectifier,
low ripple, for 3 gallons or less bath is only $300 to $500) -
Use Palladium over your base metal, THEN pink plate if you have no
major improvement with other methods. That usually eliminates the
tarnishing caused by galvanic reaction to base metals. -
Reduce the workload in the bath until you have no tarnish issues.
That could mean doing one at a time, but ZERO rework is always less
work!
Hope this is helpful! If you have Rhodium or Gold Plating or Silver
Tarnish issues, feel free to contact us! See www.davis-k.com or email
me offline
Regards,
Glenn Thompson
Davis K Products Inc.