[be advised, it's a long one]
FWIW, I just did a whole lot of etching in silver with ferric nitrate
- it was a learning experience, but a pretty successful one. I used
pretty much the method described in Karen Christians' article; the
2:1 ratio of water to ferric nitrate crystals worked out very well.
(The ratio was mixed by weight, not volume, using filtered water.) I
experimented with a more dilute solution, unscientifically reduced to
the color of weak redbush tea, but found it too pokey and went back
to the strong stuff. I did all the etching in a largish, rectangular
Pyrex dish, about 8" x 10" x 2 1/2", and suspended the pieces,
several at a time, on a chunk of styrofoam.
I started out using air stones and an aquarium bubbler, but I
removed it after only an hour or two because it was causing large
bubbles to form on the underside of the pieces being etched. (Maybe
the container was too shallow?) Placing the air pump (with nothing
connected to it) against the side of the pan seemed to speed etching
just a teeny bit, presumably because of the vibrations generated,
but I got tired of the noise and stopped using it. Maybe it took a
little longer, but sanity was allegedly preserved!
The etching was checked for progress every 30 min. at first, and
then every hour when I realized how slowly it progressed. The
unprotected areas of silver developed a dark grey or black coating,
which could be rinsed off under a steady stream of water. Gentle
brushing with a synthetic Testor paintbrush removed all of the scum
without damaging the resist.
PNP Blue was used as the resist, as the designs featured many rather
fine lines. (I was doing pseudo-champleve with Durenamel on the
final product.) The resist worked well, but began to degrade after
3-4 hours in the etchant. Burnishing it well with the iron during
the transfer process seemed to make it a little more durable - I
found it unnecessary to use a sheet of paper during the transfer
process, as the instruction sheet suggested. Fortunately, the PNP
stayed on long enough to etch the design in quite clearly, about 0.1
to 0.2 mm deep.
To replace the PNP resist when it began to peel off, I tried two
methods: handpainting with oil enamel, and applying nail polish with
a printing brayer in the same manner used for inking linoleum blocks.
Handpainting was a tedious process, and the oil enamel degraded after
about three more hours in the etchant. However, rolling nail polish
over the raised design worked well for detailed designs and could be
done quite quickly. Several coats were usually required to ensure
that all raised areas were protected, and the polish was allowed to
dry between coats. On designs with large, open areas, the polish
often went where it wasn't wanted, but it could be scraped off after
it had dried. I sometimes had to re-scrape areas after an hour in
the etchant to make sure that no polish residue was causing problems.
The nail polish was by far the best "paintable" resist, and lasted
about 6 - 7 hours before beginning to degrade. (The backs of the
pieces were covered with plastic shipping tape, which worked just
The final etch, which had to be at least 0.015" deep for the
Durenamel, took about 8 - 10 hours to reach; I did some pieces over
the course of two days, and didn't notice any ill effect from
interrupting the process. Some fine lines did get broken when I
placed pieces that were already deeply etched in fresh solution, so
it might be a good idea to check pieces more frequently when the
solution is new. Baking soda was used to clean pieces when the
etching process was complete, and left a nice sheen on the metal.
I hope these notes will be helpful to anyone wanting to try this
technique - it really wasn't difficult or even that expensive, and
yielded some very nice results.
near Lecanto, FL, where the air is full of dragonflies!