I am etching this:

http://www.flickr.com/photos/2768312...in/photostream

The electrolyte is 3500 ml H2O, 800 g of CuSO4 and 360 ml of H2SO4
(battery acid concentration - say 32.5%). The piece (anode) is
recycled brass thingy of uncertain provenance. The cathode is copper.

I turn on the current. I get 1 A with hardly any voltage at all. I do
not see a short circuit. Nothing happening in the bath.

15 minutes later the voltage goes to 2 V with the current increasing
slightly to 1.2 A. There is now a small amount of gas being produced
on the anode. It stays like this for the next 45 minutes.

The result is as shown.

Questions:
1) Is the gas oxygen? Sulphur dioxide? None of the above?
2) Why the change in behaviour 15 minutes into the process?

BTW beautiful copper coating on the cathode. Shame it was copper to
start with...

Michael Koblic,
Campbell River, BC

wrote in message
...
I am etching this:

http://www.flickr.com/photos/2768312...in/photostream

The electrolyte is 3500 ml H2O, 800 g of CuSO4 and 360 ml of H2SO4
(battery acid concentration - say 32.5%). The piece (anode) is
recycled brass thingy of uncertain provenance. The cathode is copper.

I turn on the current. I get 1 A with hardly any voltage at all. I do
not see a short circuit. Nothing happening in the bath.

15 minutes later the voltage goes to 2 V with the current increasing
slightly to 1.2 A. There is now a small amount of gas being produced
on the anode. It stays like this for the next 45 minutes.

The result is as shown.

Questions:
1) Is the gas oxygen? Sulphur dioxide? None of the above?
2) Why the change in behaviour 15 minutes into the process?


As the ( non conducting ) oxidation gets etched away, the amount of (
conductive ) surface area in contact with the electrolyte increases.


BTW beautiful copper coating on the cathode. Shame it was copper to
start with...

Michael Koblic,
Campbell River, BC