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Etching complications


#1

Hello etching experts- I’ve been searching the archives for some
time now on etching with ferric nitrate, and have etched silver a
number of times, but I am still having some complications. The
problem is that the metal is etching deeper in some areas then in
others. One half is very deep, and the other is barely etched. I
have the metal floating face down in ferric nitrate, on a wood
picture frame. There is the air stick underneath blowing bubbles to
keep the acid agitated, and it is on a warming plate. Would the
placement of the bubble wand affect the etch that much that it
etches more where it directly is hitting? Also, I etched for 6
hours, and would check it every hour to see progress. For most of
the time I couldn’t see any progress. I noticed the etched metal
wasn’t falling to the bottom, but sitting on the piece. Only when I
finished etching and scrubbed with a brass brush, could I see how
deep it etched. Am I doing anything wrong? I have been reusing the
same acid (about 5 times with same batch) but I keep adding more
acid each time). It has an orangey brown color. Thanks in advance
for any advice.- Janine


#2

Janine,

Would the placement of the bubble wand affect the etch that much
that it etches more where it directly is hitting? 

This will certainly affect it. The idea of air bubbles is to
agitate the whole liquid … if the bubbles are directed or impinging
just on one part then that area will tend to etch faster. A possible
disadvantage of using air burst agitation is that you will possibly
be creating minute droplets of ferric nitrate solution in the air
above your etch bath, so keep a lid on if possible.

Another thing you could do is thoroughly anneal the piece before
etching, so that it all has the same hardness.

I’m puzzled as to why you’re having to brush the plate to see the
depth of etch, as the etch action will be to form silver and copper
nitrate, both of which are soluble. One possible explanation would
be if you have any chloride in the bath, as silver chloride is
insoluble in water (though I don’t know how it would behave in ferric
nitrate solution). Using chlorinated tap water may be enough to
cause problems.

Good luck!
Kevin (NW England, UK)


#3

Janine:

I hope I can answer your question.

  1. Get rid of the bubbler. The acid only wants to be agitated
    enough for the silver to drop down to the bottom. Instead, use the
    pump only, and strap it to the side next to the bottom of your
    plastic container. Agitation will work very well here from the
    little pump just vibrating away. This should increase the etch
    depth.

  2. Attach the back of your silver with some duct tape. Then add a
    little double sided sticky tape to a little piece of styrofoam. You
    are making little pontoons! These were great for both types of acid
    processes.

  3. When mixing any chemicals, make sure you are using Distilled
    Water. Sometimes when you use tap water, there are minerals which
    can bind up the etching mordant (acid).

  4. I would make up a fresh bath every two times you etch. Silver
    is particularly tricky. Don’t know why, but this seems to work
    better for me.

  5. Concentration should be 1 cup of ferric nitrate to three cups of
    water.

Good luck!
-karen