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Disappointed with Edinburgh etch

#1

Hello,

I made a batch of Edinburgh etch last week using a 16oz bottle of
Ferric Chloride (Radio Shack’s PCB etchant) mixed with 1 oz of
powdered citric acid and 3 oz. hot tap water. I have to say, I was
quite disappointed with the result. I’m wondering what I did wrong. I
was etching 22ga brass plates with a PnP blue resist. It took almost
4 hours to get a decent etch, and even then, the etch was lacking
detail. Based on my research of the Edinburgh etch, I was expecting
quicker and sharper results. I had the plates sitting face up, the
temperature of my garage was about 85 or so. I was using a Lortone
6lb tumbler on the table for vibration. I’m wondering if the problem
was with a lack of adequate vibration. Should I have been using an
aquarium pump instead?

Thanks,
Alicia Istanbul

#2

Alicia, I think the problem is that you had your brass plates face
up. When etching with Ferric Chloride on copper I put them face down,
so that the debris does not collect on the surface of my piece. I
would assume that the same would hold true for etching brass.

Also, I tend to etch one piece at a time. You mention doing several
at a time. Try it again, with the metal face down, but floating, and
not touching the bottom. Attach a piece of foam to the top of your
metal with some double sided tape so that your piece will float.
Hopefully you will get a good etch.

Alma

#3 
I had the plates sitting face up, the temperature of my garage was
about 85 or so. I

I have only used the Edinburgh etch with copper. It should be face
down, so the sludge can drain away. Yes, it’s slow. That’s the whole
challenge, get the etch you want before the resist breaks down.

Etching with the safer stuff takes endless experimenting and
practice. Take notes on what you do so that when it finally works,
it’s repeatable.

Elaine
http://www.CreativeTextureTools.com ™
Hard to Find Tools for Metal Clay

#4 
It took almost 4 hours to get a decent etch, and even then, the
etch was lacking detail. Based on my research of the Edinburgh
etch, I was expecting quicker and sharper results. I had the plates
sitting face up

If you got a decent etch in 4 hours with the plate face up, then the
Edinburgh etch was working, I would say. Copper (and brass) etching
in ferric chloride produces a precipitate that blocks the action of
the mordant if allowed to accumulate on the plate, so you have rto
etch face down. One of the things that adding citric acid (why add
water?) is supposed to do is make the etched material dissolve so it
doesn’t precipitate out.

My advice would be, try again with the plate face down, no extra
water, and it wouldn’t hurt to increase the agitation.

Noel

#5

Alicia, did you use tap water or distilled? I only use distilled
because I have had slower reaction time with tap water and all the
minerals it contains here in my area. It also works much better with
the plates floating face down, the etched part will drop away from
the plate and not impede the etch. Also, it depends on where you
were using the tumbler. I use a dental vibrator on top of my dryer,
you can actually see the ferric chloride moving in the glass dish.

Donna in VA

#6

Alicia:

A couple of suggestions:

First, as several people have already mentioned, have the plates
facing downward, so the etching crud falls out of the pattern. I’ve
found the easiest way to do this is to use double-sided tape to
stick them onto those foam trays that the grocers use for meat & etc.
The tray floats around on the top of the bath, and your piece stays
on top of the bath, facing down.

I recently taught a couple of classes in ferric chloride etching,
and the thing we found most effective for boosting our etch speed was
to have the bath seriously agitated. We used a magnetic stirring
unit, with the plates floating around on top of the bath, and could
chew most of the way through 18ga brass in about 3 hours with a
fresh batch of mordent.

FWIW Brian.

PS–> always mix chemicals with distilled water. Your tap water might
be great this week…then again, it might not. Distilled water is
always the same.

#7

As others have said, hanging the plates face down will lessen the
need for agitation. I don’t think the vibration will do it. When
etching circuit boards face up, a rocker is sometimes used, which
sloshes the etchant from one side to the other. For fast etching,
etchant is sprayed on vertical boards.

Al Balmer
Sun City, AZ