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

Previously when I saw pits like these I thought it was caused by pin
holes in the resist. There was some discussion about its here. I
firmly believed that it was the hydrogen bubbles cavitating causing
this. However, in this case there is *no* resist!

Michael Koblic,
Campbell River, BC

On 10/26/2011 10:54 PM, wrote:
http://www.flickr.com/photos/2768312...in/photostream

Previously when I saw pits like these I thought it was caused by pin
holes in the resist. There was some discussion about its here. I
firmly believed that it was the hydrogen bubbles cavitating causing
this. However, in this case there is *no* resist!

Michael Koblic,
Campbell River, BC


Looks like your etch found some weak spots to exploit.

Is it like that all over? Or just along the bottom?

On Wed, 26 Oct 2011 20:54:22 -0700, wrote:

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

Previously when I saw pits like these I thought it was caused by pin
holes in the resist. There was some discussion about its here. I
firmly believed that it was the hydrogen bubbles cavitating causing
this. However, in this case there is *no* resist!

Michael Koblic,
Campbell River, BC

Was the original metal some type of casting? In that case, it could be
porosity in the original casting uncovered/opened up by the etching
process.

BTW: The sun dials you make are way cool. Do you sell them on a web
site?
Dave

On Thu, 27 Oct 2011 01:24:12 -0400, lid wrote:

On Wed, 26 Oct 2011 20:54:22 -0700, wrote:

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

Previously when I saw pits like these I thought it was caused by pin
holes in the resist. There was some discussion about its here. I
firmly believed that it was the hydrogen bubbles cavitating causing
this. However, in this case there is *no* resist!

Michael Koblic,
Campbell River, BC

Was the original metal some type of casting? In that case, it could be
porosity in the original casting uncovered/opened up by the etching
process.

BTW: The sun dials you make are way cool. Do you sell them on a web
site?
Dave

Thank you.

I have a few on Etsy:

http://www.etsy.com/shop/crquack?ref=pr_shop_more

The original metal is a 2" washer!

I have a stack of pictures of this phenomenon but in all other
instances there was an intervening resist. I thought I solved the
problem at one point by having the cathode on top so the hydrogen
bubbles would not have to go past the work piece (anode). I am now
wondering if the distance between the electrodes is critical. I did
another piece on the same day which I did not photograph. Because of
the shape of it the distance between the electrodes was very small
(1/8"). The piece was full of holes such as those shown in the
picture. This however, was a negative etch so the holes were all under
the resist. In fact you could tell the result was going to be bad when
I spray-washed the piece after it came out of the bath - the resist
starting coming off in spots exactly where the holes appeared
underneath.

Previously I attributed it to foul biting but seeing it without an
intervening resist makes me re-evaluate.

FWIW I never see this when doing brass which is a gasless process.

I am going to run a trial with several electrode distances to see if I
am right.

I have read a lot about cavitation but it is still black magic to
me:-)

Michael Koblic,
Campbell River, BC

On 10/27/2011 8:00 PM, wrote:
On Thu, 27 Oct 2011 01:24:12 -0400, lid wrote:

On Wed, 26 Oct 2011 20:54:22 -0700, wrote:

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

Previously when I saw pits like these I thought it was caused by pin
holes in the resist. There was some discussion about its here. I
firmly believed that it was the hydrogen bubbles cavitating causing
this. However, in this case there is *no* resist!

Michael Koblic,
Campbell River, BC

Was the original metal some type of casting? In that case, it could be
porosity in the original casting uncovered/opened up by the etching
process.

BTW: The sun dials you make are way cool. Do you sell them on a web
site?
Dave

Thank you.

I have a few on Etsy:

http://www.etsy.com/shop/crquack?ref=pr_shop_more

The original metal is a 2" washer!

I have a stack of pictures of this phenomenon but in all other
instances there was an intervening resist. I thought I solved the
problem at one point by having the cathode on top so the hydrogen
bubbles would not have to go past the work piece (anode). I am now
wondering if the distance between the electrodes is critical. I did
another piece on the same day which I did not photograph. Because of
the shape of it the distance between the electrodes was very small
(1/8"). The piece was full of holes such as those shown in the
picture. This however, was a negative etch so the holes were all under
the resist. In fact you could tell the result was going to be bad when
I spray-washed the piece after it came out of the bath - the resist
starting coming off in spots exactly where the holes appeared
underneath.

Previously I attributed it to foul biting but seeing it without an
intervening resist makes me re-evaluate.

FWIW I never see this when doing brass which is a gasless process.

I am going to run a trial with several electrode distances to see if I
am right.

I have read a lot about cavitation but it is still black magic to
me:-)

Michael Koblic,
Campbell River, BC



Are you agitating the solution?

On Thu, 27 Oct 2011 21:35:27 -0500, Richard
wrote:
[...]

Are you agitating the solution?


No, I am not.

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

Previously when I saw pits like these I thought it was caused by pin
holes in the resist. There was some discussion about its here. I
firmly believed that it was the hydrogen bubbles cavitating causing
this. However, in this case there is *no* resist!

Michael Koblic,
Campbell River, BC

What I remember from chemistry lectures long ago is that the components of
an alloy separate as the cast ingot cools, giving crystals of the more
stable composition surrounded by a less organized mass of somewhat different
proportions. Rolling the metal into sheets spreads out the crystals and
depending on their size (cooling rate) may make the alloy vary with location
at visible scales, like granite rock.

The junction of two different alloys has an electrical potential that is the
difference between their attraction for electrons, like a thermocouple or
battery. In a corrosive environment these slightly different alloys act like
weak batteries, so the more active material will dissolve faster than the
less active one. This is part of why rust forms isolated deep pits instead
of cutting in evenly.

Notice the uncertainty:
http://en.wikipedia.org/wiki/Pitting_corrosion

Another part:
http://en.wikipedia.org/wiki/Crevice_corrosion

HTH
JSW

On Thu, 27 Oct 2011 07:51:16 -0400, "Jim Wilkins"
wrote:


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

Previously when I saw pits like these I thought it was caused by pin
holes in the resist. There was some discussion about its here. I
firmly believed that it was the hydrogen bubbles cavitating causing
this. However, in this case there is *no* resist!

Michael Koblic,
Campbell River, BC

What I remember from chemistry lectures long ago is that the components of
an alloy separate as the cast ingot cools, giving crystals of the more
stable composition surrounded by a less organized mass of somewhat different
proportions. Rolling the metal into sheets spreads out the crystals and
depending on their size (cooling rate) may make the alloy vary with location
at visible scales, like granite rock.

The junction of two different alloys has an electrical potential that is the
difference between their attraction for electrons, like a thermocouple or
battery. In a corrosive environment these slightly different alloys act like
weak batteries, so the more active material will dissolve faster than the
less active one. This is part of why rust forms isolated deep pits instead
of cutting in evenly.

Notice the uncertainty:
http://en.wikipedia.org/wiki/Pitting_corrosion

Another part:
http://en.wikipedia.org/wiki/Crevice_corrosion


I read both several times. Interesting. I can sort of see the pitting
type of corrosion more than the crevice type. I am not sure that it is
the whole explanation. Some of the considerations that puzzle me a

1) Why would a weak local battery not be swamped by a 2.5A current
passing through the whole system?
2) Why are the pits, if they develop as described in the article, so
deep and apparently so uniform in shape (I enlarged the photo - most
of them seem comma shaped)?
3) Why does one not see similar phenomenon with brass? There I am
removing copper from zinc. One would have thought that local batteries
would if anything be "stronger".

There are other considerations derived from the previous experience of
similar pits developing under a resist. However, I am not even sure
this is the same phenomenon. The pits sure look similar.

I am going to run a few test and see what gives.

Michael Koblic,
Campbell River, BC

wrote in message
...
On Thu, 27 Oct 2011 07:51:16 -0400, "Jim Wilkins"
wrote:
....

I read both several times. Interesting. I can sort of see the pitting
type of corrosion more than the crevice type. I am not sure that it is
the whole explanation. Some of the considerations that puzzle me a

1) Why would a weak local battery not be swamped by a 2.5A current
passing through the whole system?
2) Why are the pits, if they develop as described in the article, so
deep and apparently so uniform in shape (I enlarged the photo - most
of them seem comma shaped)?
3) Why does one not see similar phenomenon with brass? There I am
removing copper from zinc. One would have thought that local batteries
would if anything be "stronger".

There are other considerations derived from the previous experience of
similar pits developing under a resist. However, I am not even sure
this is the same phenomenon. The pits sure look similar.

I am going to run a few test and see what gives.

Michael Koblic,
Campbell River, BC

The undergrad chemistry courses skimmed lightly over a very wide field of
industrial applications. They told us we weren't really chemists yet, but
when (if) we got a job in industry we knew enough theory to understand the
explanations, many of which were proprietary trade secrets. Electrochemistry
is particularly secretive about the details that make one battery better
than another. It's still black art, or FM as we say in electronics.

I did check other references. Do you really want to dive into the theory of
redox potential?

jsw

On Fri, 28 Oct 2011 08:18:53 -0400, "Jim Wilkins"
wrote:

[...]

The undergrad chemistry courses skimmed lightly over a very wide field of
industrial applications. They told us we weren't really chemists yet, but
when (if) we got a job in industry we knew enough theory to understand the
explanations, many of which were proprietary trade secrets. Electrochemistry
is particularly secretive about the details that make one battery better
than another. It's still black art, or FM as we say in electronics.

I did check other references. Do you really want to dive into the theory of
redox potential?

Not especially. Not beyond what I read in the books I have.

I spent this PM making components for a test set up (time I should
really be spending otherwise, but until I have this sorted it is hard
to move forward). I hope this will provide some insight and
confirm/refute my theory.

I should mention that I have never seen similar pitting on steel when
using a non-electrolytic process (e.g. Ferric Chloride).

Michael Koblic,
Campbell River, BC

On 2011-10-27, wrote:
http://www.flickr.com/photos/2768312...in/photostream

Previously when I saw pits like these I thought it was caused by pin
holes in the resist. There was some discussion about its here. I
firmly believed that it was the hydrogen bubbles cavitating causing
this. However, in this case there is *no* resist!

Are those truly pits, or are they projections? I could imagine
air bubbles (or hydrogen) forming on the surface which would prevent as
much access from the etchant.

Either tapping the edge every so often, or applying ultrasonics
from a cleaner might break them up fairly quickly.

Good Luck,
DoN.

--
Remove oil spill source from e-mail
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

On 28 Oct 2011 01:42:54 GMT, "DoN. Nichols"
wrote:

On 2011-10-27, wrote:
http://www.flickr.com/photos/2768312...in/photostream

Previously when I saw pits like these I thought it was caused by pin
holes in the resist. There was some discussion about its here. I
firmly believed that it was the hydrogen bubbles cavitating causing
this. However, in this case there is *no* resist!

Are those truly pits, or are they projections? I could imagine
air bubbles (or hydrogen) forming on the surface which would prevent as
much access from the etchant.

Either tapping the edge every so often, or applying ultrasonics
from a cleaner might break them up fairly quickly.


They are pits and quite deep at that. The main reason I have the
cathode on top now is to allow for the hydrogen to escape without
coming into contact with the work-piece.

I am going to try a few things tomorrow and see what pans out.

Michael Koblic,
Campbell River, BC

On 28 Oct 2011 01:42:54 GMT, "DoN. Nichols"
wrote:

On 2011-10-27, wrote:
http://www.flickr.com/photos/2768312...in/photostream

Previously when I saw pits like these I thought it was caused by pin
holes in the resist. There was some discussion about its here. I
firmly believed that it was the hydrogen bubbles cavitating causing
this. However, in this case there is *no* resist!

Are those truly pits, or are they projections? I could imagine
air bubbles (or hydrogen) forming on the surface which would prevent as
much access from the etchant.

Either tapping the edge every so often, or applying ultrasonics
from a cleaner might break them up fairly quickly.

Good Luck,
DoN.

I think DoN has the answer.

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

You could also try mechanical stirring (try a paint mixer in a drill just to
see if it helps), or maybe bubbling with compressed air (mixes ok but
evaporates lots of your solution). Helps keep surfaces uniform when
electropolishing stainless steel, and that's basically what you are doing.
Do you use just vinegar or do you add some table salt for better
conductivity? What strength vinegar? Very nice pieces, BTW.

-----
Regards,
Carl Ijames
"Gunner Asch" wrote in message
...

On 28 Oct 2011 01:42:54 GMT, "DoN. Nichols"
wrote:

On 2011-10-27, wrote:
http://www.flickr.com/photos/2768312...in/photostream

Previously when I saw pits like these I thought it was caused by pin
holes in the resist. There was some discussion about its here. I
firmly believed that it was the hydrogen bubbles cavitating causing
this. However, in this case there is *no* resist!

Are those truly pits, or are they projections? I could imagine
air bubbles (or hydrogen) forming on the surface which would prevent as
much access from the etchant.

Either tapping the edge every so often, or applying ultrasonics
from a cleaner might break them up fairly quickly.

Good Luck,
DoN.

I think DoN has the answer.

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

On Oct 26, 10:54*pm, wrote:
http://www.flickr.com/photos/2768312...in/photostream

Previously when I saw pits like these I thought it was caused by pin
holes in the resist. There was some discussion about its here. I
firmly believed that it was the hydrogen bubbles cavitating causing
this. However, in this case there is *no* resist!

Michael Koblic,
Campbell River, BC

Non-uniform alloy, just like the other poster said. You can also get
this with higher carbon steels when removing rust with phosphoric acid
or the like. Preferential etching at certain grain boundaries. Get
some lower carbon material and more uniform. Non-metallic inclusions
can also get etched out and leave pits, too. Without polishing,
etching and viewing a sample under a microscope, it's just
speculation, though.

Stan

On Fri, 28 Oct 2011 09:08:12 -0700 (PDT), wrote:

On Oct 26, 10:54*pm, wrote:
http://www.flickr.com/photos/2768312...in/photostream

Previously when I saw pits like these I thought it was caused by pin
holes in the resist. There was some discussion about its here. I
firmly believed that it was the hydrogen bubbles cavitating causing
this. However, in this case there is *no* resist!

Michael Koblic,
Campbell River, BC

Non-uniform alloy, just like the other poster said. You can also get
this with higher carbon steels when removing rust with phosphoric acid
or the like. Preferential etching at certain grain boundaries. Get
some lower carbon material and more uniform. Non-metallic inclusions
can also get etched out and leave pits, too. Without polishing,
etching and viewing a sample under a microscope, it's just
speculation, though.

I would buy that if I ever saw similar pits using Ferric Chloride. I
never do.

I would go back to using FeCl3 but the depth of etch is so much better
with this process. As often as not I get a clean etch. It is the
unpredictability that irks me.

Michael Koblic,
Campbell River, BC

On 2011-10-29, wrote:
On Fri, 28 Oct 2011 09:08:12 -0700 (PDT), wrote:

On Oct 26, 10:54*pm, wrote:
http://www.flickr.com/photos/2768312...in/photostream

Previously when I saw pits like these I thought it was caused by pin
holes in the resist. There was some discussion about its here. I
firmly believed that it was the hydrogen bubbles cavitating causing
this. However, in this case there is *no* resist!

Michael Koblic,
Campbell River, BC

Non-uniform alloy, just like the other poster said. You can also get
this with higher carbon steels when removing rust with phosphoric acid
or the like. Preferential etching at certain grain boundaries. Get
some lower carbon material and more uniform. Non-metallic inclusions
can also get etched out and leave pits, too. Without polishing,
etching and viewing a sample under a microscope, it's just
speculation, though.

I would buy that if I ever saw similar pits using Ferric Chloride. I
never do.

I would go back to using FeCl3 but the depth of etch is so much better
with this process. As often as not I get a clean etch. It is the
unpredictability that irks me.

How consistent is your metal supply? If you buy mild
(low-carbon) steel and process it, you will probably get fairly
consitant results. If you use a lot of "found" or "mystery" metal, then
you don't know what alloy you have, and have to expect variable results.

And buying large washers from the local hardware store leaves
you open for almost any flavor of alloy -- often from the same bin. :-)

Good Luck,
DoN.

--
Remove oil spill source from e-mail
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

"DoN. Nichols" wrote in message
...
...
And buying large washers from the local hardware store leaves
you open for almost any flavor of alloy -- often from the same bin. :-
DoN.

I don't know about their alloy but the thicknesses can vary considerably
within the bin.

Half a foot of snow in October???
Support Global Warming!

On Sat, 29 Oct 2011 07:25:38 -0400, "Jim Wilkins"
wrote:

"DoN. Nichols" wrote in message
...
...
And buying large washers from the local hardware store leaves
you open for almost any flavor of alloy -- often from the same bin. :-
DoN.

I don't know about their alloy but the thicknesses can vary considerably
within the bin.

Half a foot of snow in October???
Support Global Warming!

In truth everyone has a valid point although I am not sure that it
explains the problem entirely.

I am about to give up using washers, at least the 2" variety for the
very reason you state: The thickness varies quite a bit, the quality
varies also. Their availability has decreased: I used to be able to go
to Fastenal and rummage in their bin and pick the ones that were
useful. Fastenal no longer stock them. You can order them but then you
have to take what they send you.

Anyway, to confuse matters further: Here is the first trial I did
today:

http://www.flickr.com/photos/2768312...7627882701769/

Make of it what you will. The next thing is to try increase the
distance between the plates and/or try to run the whole assembly on
its side so the bubbles have a free exit.

I included a picture of a piece that ended up like pig's breakfast
just to show that whatever it is that causes the pits it blasts its
way through 4 coats of resist if the conditions are right.

That is always assuming that the cause of the pitting in the different
pieces is the same.

Michael Koblic,
Campbell River, BC

Our temperatures have been sub-normal practically whole year. Either
it is not warming or it is not global:-)