Thanks Carl. Despite my efforts, I'm still doing electro-dulling! Your
comment about using copper for the cathode might be what I'm missing.
I've been using SS for the cathode. I think my lack of success is due
to a combination of things. Wrong cathode material, electrolyte out of
balance, and low electrolyte temperature. I have however played with
various current densities. One other thing I have learned is that by
using 308 stainless wire (commonly used in MIG welding) as wire
hangars, there must be enough of an iron content to dirty up the
electrolyte with a reddish-brown emission.

Back to the lab... more later.
Thansk to all,
Dan

"Carl Ijames" wrote:

I've been experimenting with electropolishing stainless steel with
limited success. I've tried various electrolytes - hydrochloric acid
(not good), citric acid (better, but still etches my part), and
Phosphoric acid (more aggressive than citric, but still does not
polish well). I have tried various current densities, but still get
the same results - light frosting (sort of like a fine bead blast
finish), but no bright polished finish.I'm using anodic polarity with
the part to be polished connected to the power supply (+) and the
cathode (also stainless) connected to the (-) terminal. I have looked
at the finishes under a microscope and can see the reason for the
lack-luster finish. I have also read several postings, etc. where
various blends of sulfuric and phosphoric acids and am wondering if
this is my problem. Does anyone have any experience with electrolytes
used to electropolish? Any hints would be greatly appreciated. BTW,
the stainless I'm working with is 303.

I've done some 304 with phosphoric/sulfuric acid solutions, and with
citric/sulfuric acid solutions, and a little 316, but not any 303. Go
to google groups and search for "electropolish ijames" and you'll find a
long posting I made here giving recipes and conditions. If the solution
conductivity or ionic strength isn't right it is really easy to
"electrodull", which is what my coworkers call your frosted, dull finish
:-). The cathode composition is also important; I get good results most
consistently with copper. Here is an excerpt:

[quote]
However, I have used 50 parts of
citric acid and 50 parts battery acid with good results. This solution
is supersaturated with citric acid at room temperature so all will not
dissove without heating, and some some citric acid will precipitate out
each time you cool the solution but it seems to redissolve okay with
heating the next time the solution is used. I started with about 1/2
cup of each acid in a small bowl, and then gave the bowl about a minute
and a half in a microwave oven which made it too hot to touch but got
all the citric acid dissolved. I then electropolished some small
pieces, between one and four square inches, and got nice polishing
action between about two and 10 amps/sq. in. with about 3 sq. in. of
copper sheet as cathode, which was a little on the small side. Below
that it really didn't seem to damage the surface, but the polishing was
so slow it wasn't worth doing - I got noticeable brightening after about
4-6 minutes at 2 amp/sq. in. and a nicely polished surface after about a
minute or two at 5-8 amps/sq. in. Ten amps/sq. in. was okay but the
foaming was pretty bad in my litte test bowl. I was also impressed with
[endquote]