Etching Sterling with Rectifier

Jewelry Discussion
1

Hi All, I need your help to solve this puzzle! After reading some of
the Orchid member comments re. etching sterling with ferric nitrate,
I went into the archives and retrieved all necessary
Went out and purchased a rectifier (rated 15 volts, 40 amps) from a
jewelry tool supplier here in LA. I assume the rectifier is sold for
use in plating. My settup is as follows: Cylinder shape plastic
container (10.5 cup capacity, 7" high, 6" diameter), filled (up to
1" from top) with distilled water in which ferric nitrate crystals
have been dissolved to achieve the color of coffee. The cathode
(titanium, paddle shape) is attached to the negative lead. The
sterling to be etched (from 24 - 16 Ga, all sizes) has a hole
drilled in the top portion and is suspended in the ferric nitrate by
a 12 Ga sterling wire S hook, to which I attached the positive lead.
The titanium is approximately 4" from the sterling to be etched.
ProceduRe: I immerse sterling in ferric nitrate, make sure that the
cathode and the sterling sheet are parallel to each other, turn on
the rectifier and set voltage to 10. The etching usually takes
1.5-2.5 minutes. Each time I take the sterling out of the solution
(to inspect and clean off the sludge) I turn off the rectifier and
turn voltage to 0. For resist I use PNP, and packing tape on back
and edges of the piece. The first time I used the rectifier, I did
not go over 10-12 volts, it lasted about 3 hours. Then it stopped
working, I have no idea why. The etching results up to this point
were good. I took the rectifier back to the supplier and exchanged it
for a new one (same model). I did some etching on two more
occasions, in the middle of the second session the volts went to
maximum (15) and to 0 amps, and could not be adjusted (fuse was ok).
Since then I have returned the second rectifier. The supplier can
not give me any guidance because they have not heard of anyone using
the rectifier for etching purposes. There are 3 problems I need help
with:

  1. Rectifier (sources, make, description) and what you think I’m
    doing wrong.

  2. The etching is much deeper on the bottom of the sterling piece, to
    the point that I occasionally have small holes in the bottom of the
    piece.

  3. The 12 Ga sterling wire S hook gets etched to nothing (after a
    short while) and the piece falls to the bottom.

I really enjoy etching, if only I knew what is wrong with my process.
I would greatly appreciate every ones help, so that I can get on with
my life and with my etching.

Mimi Grabis

2

Hi Mimi, I’m going to answer your questions in reverse order. Your
sterling S-hook gets etched to nothing because the ferric nitrate
etches sterling silver. Like the holed produced in your sheet, so
too goes the hook. I would suggest a different metal (like titanium)
as a hook. Holes on the bottom - that’s a tough one. Technically, if
your set-up is correct, the area of greatest etch is the side closest
to the titanium where the current density is greatest (at this point
I’m assuming that the titanium and the silver are both flat pieces of
metal). It’s possible that the bottom is where the ferric nitrate
has the greater effect - I’m thinking the reason would be that the
silver nitrate (from the etch) doesn’t have the chance to collect in
any recesses, your metal would therefore always present a clean
surface for etching whereas the body needs to be cleaned. Finally lets
have a look at your set up. For etching I’m assuming that the silver
is attached to the positive terminal (the silver is the anode) and
the titanium is attached to the negative terminal. Your problem
might be that the electrolyte is depleted (thereby slowing or halting
the flow of electrons between metals). You may need to refresh the
solution. It may be that the ferric nitrate is not a good
electrolyte and that the only reason you’re etching at all is the
presence of the ferric nitrate (that would explain the slow etch
times) and not because of the flow of electrons. Try etching using
sodium bicarbonate (15% in hot water) and no ferric nitrate. You can
also double check the electron flow with a multimeter. It might be the
titanium (but at this stage, we’re reaching) - try replacing it with
a piece of corroded iron.

I hope this helps.
Eileen