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[Technique] Photoetching


#1
    But ferric chloride won't etch silver. You do need strong
nitric acid for that, or it can be done electrolytically in a
sodium cyanide bath.  Don't like cyanides either? Sorry, but I
don't know of anything else which dissolves silver easily. 

Try ferric nitrate. It is much safer to use and to store than
nitric, although it may be harder to find. Try buying it in dry
form from a chemical supplier. Commercial grade will do fine –
reagent grade costs too much. Ferric Nitrate etches very slowly
and gently, giving a clean cut with little undercutting [unlike
nitric]. You can use very thin resists [rosin, soft ground, hard
ground, paint markers, graphics tape, PnP tranfers, etc.] and get
lovely results, even on very fine detail. I do a lot of niello
inlay of very fine line drawings on silver using hard ground as
my resist, and the results are beautiful. Ferric nitrate should
be used with rubber gloves since it will turn your skin a bright
and durable yellow.

I use my anodizer to get a faster etch. This was an idea that
Charles Lewton-Brain discussed at a bench tips free-for-all at
SNAG '97. He suggested using electricity to speed up reactions,
and this really does work. I use a titanium cathode in my ferric
nitrate bath, and the piece to be etched is the anode. The
amazing thing is how little voltage it takes to make a huge
difference: I never go higher than 20V, and usually work at 10V.
For some of my applications, I have been able to get an etch in
45-90 seconds that used to take nearly four hours. And the
quality is better because the resist isn’t sitting in the bath
all that time, getting ratty around the edges. Note: don’t do this
with ferric chloride since the electricity will break down the
chemical and you will get chlorine gas, which is toxic to you.

When etching in ferric nitrate, it helps to hang the piece
upside-down in the bath, and to periodically brush it with a
feather, since there is a rapid build-up of sludge on the metal
that will slow and even stop the etch unless you remove it.

     At sunny  Nelson NZ  in late winter/early spring with
lambs, daffs, tree blossoms, Cold starry nights, cold sunny
days 

In muggy late summer Franklin MA with rampant tomato vines, pole
beans run riot, goldfinches on the feeder, and a woodchuck
hassling my gourd plants…

Anne Hollerbach


#2

Thanks Anne for the great tip about the ferric nitrate! I’m
definitely going to try this. Do you need to neutralize it with
anything after you’re done etching? What concentrations do you
use? (I’m assuming it comes as a dry salt.) If you don’t use an
anodizer, how long can you expect to leave silver in the etch
bath for a significant etch? (Textural, not just visual.)

A good chemical supplier for artists is Bryant Laboratory, Inc.
in Berkeley, CA. They do a lot of mail order. Phone # is
(510)526-3141 or (800)367-3141. When I read your post about
ferric nitrate I pulled out their chemical list and they carry
it. It’s $15.95/pound and there’s a hazardous materials charge on
the shipping.

So we can use PnP on silver! Fantastic!


#3
 The amazing thing is how little voltage it takes to make a
huge difference: I never go higher than 20V, and usually work
at 10V. 

Interesting, the difference in perspectives on voltage between
those used to reactive metal anodizing, and those used to
electroplating. electroetching is essentially the reverse of
electroplating, with similar voltage requirements. Silver nitrate
chemistry, either plating or etching (the bath doesn’t care
whether your anode is just an anode, or whether its your
workpiece, as is the case with electroetching as your doing)
requires only very low voltages, on the order of 2.5 to 3 volts.
higher voltages will increase current density and etching speed,
but are not actually required for the process to work. To the
precious metal electroplater, voltages much over 12 volts are
almost never needed, and many baths are designed to run in the 3
to 6 volt range.

Anodizing, on the other hand, asks the process to force an
electric current through an insulating oxide layer, with the aim
of increasing the thickness of the oxide until the interference
colors produced by that oxide layer’s thickness are what’s
desired. Doing this takes much higher voltages than ordinary
electroplating, which are sending currents through highly
conductive solutions and through highly conductive metal
surfaces. Reactive metal oxidizing/anodizing takes higher
voltages than the other main anodizing process, aluminum, since
aluminum’s oxide layer is initially porous and somewhat more
conductive.

One thing you’ll note, though, if you think about it, is that
although anodizing titanium or niobium (etc.) takes higher
voltages, the actual current density (amps) is often very small
or even negligable. If your anodizer has an ammeter, you’ld be
surprised at how many amps can be flowing through your siver
nitrate bath and silver workpiece with even a few volts. These
highly conductive solutions pass current easily, making it
actually quite difficult to get a high voltage through the
solutions if the workpiece has any significant surface area
involved, since fuses on the power supply blow out from high
amperages before high voltages are reached…

Peter Rowe


#4

A good chemical supplier for artists is Bryant Laboratory, Inc.
in Berkeley, CA.

Rene - Thank you for your !! I had just had a
dreadful experience with one supplier (which was referred to me
by the person who taught my granulation workshop). They wouldn’t
do business with me because I did not have an appropriate
degree…and then they asked me for the name of the person
who recommended them !

Your will shorten my search considerably.

Laura Wiesler
Towson, MD.


#5
Do you need to neutralize it with anything after you're done   etching?

I rinse the piece thoroughly in warm soapy water. The reaction
between ferric nitrate and silver is slow and steady, not
carnivorous they way nitric acid is. When I have the depth I
want, I rinse the piece, remove the resist [more on that later],
and scrub the whole thing with an old toothbrush and a sloppy
paste of baking soda.

What concentrations do you use? (I'm assuming it comes as a dry  salt.) 

It comes as a dry salt and as a liquid. I highly recommend the
dry salt over the liquid since the liquid does have a shelf life
[not a short one, but it does fade with time]. I mix enough dry
salt into distilled water to make it look like good coffee [with
a yellow tinge…bleh]. Use a high quality tupperware-type
container with a lid that seals tightly. Work in an area that
will contain all spills; ferric nitrate has the odd
characteristic that it doesn’t seem to “dry” – little splatters
stay wet and kind of sticky for a long, long, time. And they
stain like the dickens. It might be worth a glace at Oppi
Untract’s big jewelry technologies book to see if he gives an
exact amount to mix with water. If you don’t have the book, just
holler…

If you don’t use an anodizer, how long can you expect to leave
silver in the etch bath for a significant etch? (Textural, not just visual.)

Since I didn’t use an exact formula to mix my bath, I won’t get
the same results that you will. Always do test strips – and if
you’re using the bath heavily, do one every now and then to see
if the solution is becoming exhausted. This is also a great way
to test different resists. Start out with the entire strip
covered [see diagram below] and etch for 30 minutes. Remove some
resist and etch for 15-20 minutes more, having brushed off the
sludge with a feather. Pull it out and remove more resist, and
put it in for another 15-20 minutes. Keep this up, with a
careful record of your times until you get the depths you want.
It can take up to four hours, with periodic gentle brushing, to
get a really deep etch. But it will be a clean etch, with
little undercutting and a very uniform result. Great for detail
work. Try this pattern for your test strips:

|  resist				|
|_______________________________________|
|					|
|  area used for test							 |	
|_______________________________________|
|  resist				|
|_______________________________________|

Be sure to cover the edges and back. I use a permanent paint
marker for the edges and well-burnished-down contact paper for
the back. By leaving some resist on the sides and doing your
test down the middle, you will get a sense of how much
undercutting will/won’t happen over time.

Agitating the bath will noticably speed the etch, since it
shakes the sludge off and mixes air into the reaction. Get a
cheap little bubbler motor from your local pet store and a length
of air tubing. Punch a hole in the top of the tupperware near
one corner [the old hot nail technique – smelly but effective]
that will allow the air tube to enter the bath. Suspend your
piece etch-side-down and run the air line in under it [not in
contact, but nearby]. Snap the lid on, plug in the pump, and let
it burble away. The lid will intercept the fine spray from
popping bubbles.

A few notes on resists:

  1. Daniel Smith Artists Supplies in Seattle WA carries a wide
    range of resists for etchers. Some of these come in forms that
    cost more to ship because they contain flammable solvents; others
    can be purchased in ball or lump form, ready for you to mix at
    home – a lot cheaper and easier to store. I use hard ground,
    stop-out varnish [used to touch up leaks in hard ground], and
    rosin. Buy the rosin in lumps, then grind it up in a mortar and
    pestle. Sift the crushed stuff through a couple of gradations of
    screen or cloth to get different sizes of particle. You then
    sprinkle or sift the particle onto your squeaky clean metal and
    GENTLY [like with a distant Bic lighter] heat the metal until
    the little fragments melt and adhere to the metal. By using
    gradations of large to small particles, it is possible to get
    stunning textural transitions on a piece. I enamel over the
    resulting etch, then stone back to the original level of the
    metal, giving a fabulous color effect either by itself or under a
    transparent color.

  2. Remove resists with the least toxic solvent possible. To my
    considerable delight, the commercial cleaner “Goo Gone” works
    perfectly on every single resist I use. Orange oil in its pure
    form works faster, but it will irritate your skin and can be hard
    to find at a reasonable price. Goo Gone uses orange oil as its
    active ingredient, but its gentler on the skin, easy to get, and
    cheap. No more mineral spirits in this house! Be sure and use a
    good detergent [e.g. Dawn] after the Goo Gone has taken all the
    resist off, since it will leave an oily film [and a lovely citrus
    smell] that must be removed.

Let us know how it goes!

Anne Hollerbach
@alhollerbach