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

On Sat, 26 Nov 2011 20:07:42 -0800, mkoblic wrote:

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

The brass stuff does look an awful lot like bubbles clinging to your
resist. How opaque is your CuSO4? Can you visually monitor the process?

If you are using something like vinyl letters for resist, and there is
air trapped under the letters then it might expand and come out with heat
-- but if that were the case I would expect some undercutting.

When folks etch circuit boards they gently agitate the etchant, the
board, or both -- the two methods that I've experienced personally are to
keep tilting the tray with the board and etchant, or to put the board
edge-on into a bath that has a bubbler on the bottom.

--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?

Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com

fired this volley in
:

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

Mike, as is the case with ferric chloride and copper, although the CuSO4
etch is gassless, produces regions of 'depleted' plating solution (in
this case, overloaded with zinc salts and copper that hasn't yet joined
up with a free sulphate radical).

I suspect, too that there are small convection currents rising from the
surface that might cause "cells" much like the granularity you see in
thinned aluminum paint, when it's stirred.

In any etching I've ever done that required completely uniform action, I
agitated it with a fish tank aerator and an air stone (if the stone was
compatible with the solution). Sometimes etching "face down" will also
benefit when there are heavier-than-water things crashing out of solution
during the process.

LLoyd

On Sat, 26 Nov 2011 20:07:42 -0800, wrote:

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


They are obviously plugs put into the base metal.
What was the base..some sort of saw blade? It has the knock out in the
center

Gunner

One could not be a successful Leftwinger without realizing that,
in contrast to the popular conception supported by newspapers
and mothers of Leftwingers, a goodly number of Leftwingers are
not only narrow-minded and dull, but also just stupid.
Gunner Asch

Gunner Asch fired this volley in
:

They are obviously plugs put into the base metal.
What was the base..some sort of saw blade? It has the knock out in
the
center


That was odd, but I assumed he'd soldered a thin sheet of brass to a saw
blade backing.

He did say he was etching brass, not steel.

It's not out of the question that the conductivity of the whole affair is
different over the "cutouts".

Lloyd

On Sun, 27 Nov 2011 12:32:45 -0600, "Lloyd E. Sponenburgh"
lloydspinsidemindspring.com wrote:

Gunner Asch fired this volley in
:

They are obviously plugs put into the base metal.
What was the base..some sort of saw blade? It has the knock out in
the
center


That was odd, but I assumed he'd soldered a thin sheet of brass to a saw
blade backing.

He did say he was etching brass, not steel.

It's not out of the question that the conductivity of the whole affair is
different over the "cutouts".


The brass piece is 2.5"x2.5" of 0.020" stock. The hole in the middle
allows a 10-32 screw to hold it to a 1" plastic spacer. The other end
of the spacer is attached to the cathode:

http://www.flickr.com/photos/2768312...57625256724344

I had the assembly with the anode "face down" i.e. on top as there is
a lot of copper chunks falling down on the cathode. I was not
observing the process very closely as I have done it hundred times
before the same way with other pieces and had no problems. That was,
however, using a commercial copper-plating electrolyte. I do not have
enough of it so I made a bigger batch from scratch. The main
difference: I omitted the sulphuric acid.

I should probably get some and try it again with it as well as watch
more closely for the bubbles.

Michael Koblic,
Campbell River, BC

fired this volley in
:




Mike, I don't know what picture you think you showed us, but that was
definitely a saw arbor knockout (or a perfect imitation of one) in the
middle of that brass face.

I don't know of any brass circular saw blades, so I assumed you'd
soldered brass to a steel blade.

You need to look at the picture you showed us.

LLoyd

On Sun, 27 Nov 2011 20:49:38 -0600, "Lloyd E. Sponenburgh"
lloydspinsidemindspring.com wrote:

fired this volley in
:




Mike, I don't know what picture you think you showed us, but that was
definitely a saw arbor knockout (or a perfect imitation of one) in the
middle of that brass face.

I don't know of any brass circular saw blades, so I assumed you'd
soldered brass to a steel blade.

You need to look at the picture you showed us.


This one?

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

It's what I said in the previous post.

Michael Koblic,
Campbell River, BC

fired this volley in
:

It's what I said in the previous post.


So what the heck is the diamond-shaped object in the middle, partially
obscured by un-eroded brass, and partly _clearly_ parted from the body
material?

Lloyd

On Mon, 28 Nov 2011 20:35:47 -0600, "Lloyd E. Sponenburgh"
lloydspinsidemindspring.com wrote:

fired this volley in
:

It's what I said in the previous post.


So what the heck is the diamond-shaped object in the middle, partially
obscured by un-eroded brass, and partly _clearly_ parted from the body
material?

Actually it is not a diamond. They are just two lines at an angle
(they are really three if you look closely - the right side is a
double line). They are lines left over from the previous use of this
particular piece which got partly obliterated when I cleaned the piece
for this experiment and then got obliterated completely by the etching
process everywhere else except in this particular spot where they were
protected by the spacer.

Michael Koblic,
Campbell River, BC