I was testing a new batch of CuSO4 solution for electrolytic etching
on a scrap piece of brass. The result is he

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

I am puzzled at the circular defects which are exclusively associated
with the numbers. The only answer I could think of was more bubbles,
but why? This is a process that does not generate any gas so unless it
is the dissolved air coming out due to heating (about 25W dissipated
in the bath) I just cannot explain it. Also, why are the defects
present only inside or over the numbers? I do not see them anywhere
else.

I have done electrolytic etching with brass before but not a
"positive" etch like this one. Never seen a similar phenomenon before.

On the bright side the steel etching is working like magic:

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

Michael Koblic,
Campbell River, BC