However, I know that rodium is fussy and easily contaminated and cynaide
is downright dangerous.
As I don't know the model of pen plater you are refering to, I can only
give some general hints:
1. yes, rhodium baths are easily contaminated, you should work cleanly and
replace the felt tips when they start to discolour. have them sharpened
with a scalpell to a very slender point.
2. cyanide can be lethal, deadly dosis is said to be about 0.2g (3 grains
troy) if one would swallow it. It also releases prussic acid (HCN) into
air on contact with any acid, even the carbonic acid naturally contained
in the air; lethal dosis 0.1mg per kilogramm bodyweight. So, you should
have some form of ventilation, even as you are working with very small
amounts. Keep the containers closed when not in use, use a working
container with just enough liquid for the job at hand. NEVER use the pen
for rhodium with a cyanide bath!!! Rhodium plating liquids are acids.
However, I never heard of anyone poisoned in using a pen plater (and I've
been working in Pforzheim and Idar-Oberstein where every third house
contains some kind of jewellery workshop).By the way, poisoning is by
blocking the transfer of oxygen from blood to body cells, so one is
actually suffocated, body just stops breathing.
Can they be built?
You'd need only purchase the pens and tips from your jewellery supplier.
There is a platinum wire in the pen due to the highly corrosive liquids
used. Buy any transformer that gives you the necessary output (up to about
5 volts). Wire the plus outlet to the pen and the minus to a self locking
tweezer to hold your ring. This should be much less expensive than buying
the whole unit (here at last).
Soak the tip until it is satiated. Have it "floating" in the liquid on the
surface and don't press to hard or you will scratch the metal without
getting a satisfying plating.