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Blue acid?

Hi all,

I work in a pawn shop, where we use nitric acid to determine whether
something is gold or not. It’s in a little glass acid jar with a lid
and a stick. Recently it has turned a lovely turquoise blue color.
Why is this? I figured maybe someone dropped a bit of metal in it or
something. Does anyone know if the color change will affect its
usefulness? I don’t want to neutralize it and throw it away if it’s
only a cosmetic problem.

Please respond off-line, I have rarely had the luxury of enough time
to read the whole list daily recently!

Thanks a lot, y’all!
Julia Newton
Willandjulianewton AT

Hi, Julia.

Copper will turn nitric acid blue. (When I was doing copper
enameling our HNO3 pickle was always deep blue.) I doubt it will
affect its usefulness; the color is just a bit of copper nitrate.
There should still be plenty of nitric acid present.



I had the same thing happen with a batch of 1:1 nitric acid solution
when I used it to etch brass. (I was making a fancy slide clip for a
microscope–I had way too much time on my hands back then!) Anyway,
it too turned a beautiful turquoise (maybe this has something to do
with copper going into solution?), but it continues to work to this
day. I think I’ve had the solution for about six or seven years and
just recently used it with great success.

So, etch on!
Jessee Smith

Hey all :slight_smile:

Pickle turning a bluish or turquoise color is the result of copper
sulfate entering the solution.

Mark Moretti
Alexandria, VA