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Etching copper and chenier rings


#1

Hi everyone! I have been working on some silver chenier rings, and
used copper wire inside to hold the form while these were bent
around a mandrel to create the ring shape. Now I am stuck with
chenier rings with copper inside, and am wondering what I can use to
etch out the copper. I have read that you can use Nitric acid, but
am not sure as to the proportions/recipes for this process. Can
anyone enlighten me? And is there an easier process to create
chenier rings without having wire inside to hold their form? Thanks
everyone!

Catherine Chandler


#2
   Now I am stuck with chenier rings with copper inside, and am
wondering what I can use to etch out the copper.  I have read that
you can use Nitric acid, but am not sure as to the
proportions/recipes for this process. 

Don’t use Nitric. While it certainly will etch the copper very
nicely, it will etch and dissolve the silver just as quickly.
Instead, use sulphuric or hydrochloric. HCL won’t dissolve the
silver, but will leave the surface slightly “smutty” looking, with a
silver chloride surface. (The reason it doesn’t destructively
attack the silver is that although it DOES initially attack the
silver, it quickly creates a thin silver chloride surface layer
which is insoluble, sealing the surface and preventing much further
attack.) Sulphuric, if hot and concentrated, will slowly attack the
silver, but use it fairly dilute, and not quite so hot, and you’ll be
fine. In that form, it’s no different from your pickle solution in
terms of it’s effect on the silver. The copper will take some time
to etch out. For a safer, and yet slower, etch, use ferric
chloride, a salt of hydrochloric acid which retains the ability to
etch/dissolve copper, though more slowly. It’s used to etch circuit
boards. You can expect this etching process to take quite some time,
if the silver tube/chenier has no seam that’s open on the side to let
in the acid. If you use the actual acid (sulphuric, I assume), it
will etch faster if it’s diluted than if it’s very strong. (odd, but
that’s how this works). Any dilution from about ten percent acid to,
I’d guess, thirty percent acid, will work. Like I said, this is
going to be sloooowwww, if that’s properly seamed tubing. Like,
days…

 Can anyone enlighten me?  And is there an easier process to create
chenier rings without having wire inside to hold their form?  

A wire core is commonly used when drawing tube smaller in a draw
plate, if one needs a core to define the interior size. After
annealing, the core can then be drawn back out. And it can be used to
bend tube, as you did, if the tube is open on the side, an
incompletely closed tube, since then the open seam on the side allows
acid easily into the tube to etch out the copper or other core… Then
it’s not so bad to etch out, and chain manufacturers sometimes use
this method to form thin tubes into chain link.s but with solid,
seamed, tubing, you are much better off using something a lot easier
to remove. Sand, pitch, or one of the very low melting metals like
babbitts or woods metal, which can be removed by simply heating the
tube till the stuff melts and pours back out, are much better
choices.

Peter