Spot etching without total immersion

Hello Orchidians,

Is there a technique by which one can create spot etching without
total immersion of the piece?

I’m working on a necklace using copper and silver. There are several
units which will comprise the finished piece, each of which is
intricately cut and layered with the two metals and each has several
minute half rings on the back, so I’d rather not remake the units if
I can get around it.

The source of the inspiration is the movement of underwater kelp
beds on the Pacific coast. Now that I have all of the layers
soldered, rings in place on the back, and the stones set, I see it
differently. I keep looking at it and seeing how it would "really"
work so much better (sigh) with a tiny etched pattern like a strand
of bull kelp in a particular shade of blue/green patina running
along three of the units. I thought if I ignored it for awhile this
vision would go away but it hasn’t.

I obviously can’t emerse the pieces in ferric chloride. I’ve
experimented with a test where I coat the back with the rings in a
few layers of beeswax and then, using a tjanting build the wax up on
the front of the unit into a dam around the area I want to etch,
coating the rest of the top in wax. The unit, now blob like with all
of the wax protection, is stuck onto a square of wax for stability,
keeping the top level. This sits in a glass bowl for safety.

The design is created with a fine point paint pen on the metal
surface. Into this “lake” with its wax levee (which is the only place
left where there is a bit of bare metal showing in the design), I put
ferric chloride until I get an etch and then I neutralize it. I can’t
agitate it so the etch process takes longer than it normally would.

This worked on the test, but I wonder: is there is another way to do
this? I made some tests using various surface treatments and none
gives the kind of watery, flowing image that an etch can do. I also
would like to make this work for future use because it uses so much
less chemical to just put it on the spot rather than make a bath.


Is there a technique by which one can create spot etching without
total immersion of the piece? 

I don’t know if anyone does this as an etch process put consider
using a galvanic electo-etch technique with a pen plating system. I
have lots of on electro etching and do it but not with a
pen technique. However I also do some pen plating. It doesn’t take
much to put the two together as a technique. SEE: The first one
includes a cyanide etch which I wouldn’t recommend but here it is for
Acid Free Non Toxic Etching
Galvanic processes. Polymetaal.

Remember that plating is the reverse of etching. the equipment is
the same -electrical connection is reversed. The electrolyte is
simpler for etching in that it just needs to be conductive. no
special metal is needed for the Cathode (Negative -) the (Anode Plus
+) is the material removed. The cathode may be able to be your base
piece. The electrical supply for a small system can just be a small
battery. Dalmar makes inexpensive pens. pens are available from most
jewelry supply houses.

Study for more ask.