Inconsistent Etching Results

Hi Folks -

I’ve been etching silver for the last few months using Nitric Acid
diluted with water, three parts water to one part Nitric Acid.

I’ve used the same solution four or five times. The last time I used
it, I got the best, most deeply-etched results. This time I put the
silver in the solution and saw very few bubbles. I stopped the
process using baking soda in a separate container, and tried again
the next day. The second day I saw a lot more bubbles, but with the
exception of one side of one piece, did not get a deep etch at all.

The difference between the two days was that the first day I used it
outside as I usually do, but instead of doing it in the afternoon, I
had to do it in the morning which was cloudy and cool. The second
day was in the afternoon, which was warmer and sunnier, which are
the conditions under which I’ve been accustomed to using it.

So, my questions aRe: is my solution simply spent? Does the
temperature make a difference? Can spent solution be revived or
should I buy more Nitric Acid and make new solution?

And last, about PNP Blue: I’ve finally figured out the right setting
on the iron and the right length of time to iron it on so that the
resist stays on and doesn’t get lifted off by the acid, but I have
been having a helluva time getting it off after etching. After much
experimentation, it seems that nail polish remover and a cotton
ball, changed frequently work the best, but it’s not easy and my
arms and hands get very tired.

Does anyone have a better suggestion?

Thanks,
Linda

Linda,

Acetone will take the toner off very quickly without effort.

Dolores

Hi Linda.

regarding removing PNP after etching. I was taught to soak the etched
piece in pure ammonia (cover it up, so that it does not weaken from
evaporation). Soak it for a while, then use a brass, or steel
bristled brush to remove the PNP. It has worked for me. I usually do
this outdoors in the shade because the ammonia fumes can be
overpowering.

Hope this helps. Alma

So, my questions are: is my solution simply spent? 

To some degree, probably yes. Addition of a little more nitric acid
will help to refresh it. Also decant the liquid from the settled
sludge (carefully!) so the sludge will not interfere with your
etching results.

Does the temperature make a difference? 

Yes, temp does make a difference, but do not make the mistake of
heating up the solution. Over 125 degrees F., and you will start
outgassing, possibly overcoming a noncommercial venting environment.
It’s best to go slower anyway to obtain a more even etch without
undercutting.

And last, about PNP Blue: I've finally figured out the right
setting on the iron and the right length of time to iron it on so
that the resist stays on and doesn't get lifted off by the acid,
but I have been having a helluva time getting it off after etching. 

MEK (methyl ethyl ketone) works best chemically, but do you really
want to use that? Best is to remove it by abrasion, either a piece
of plexiglass or those foam bars used for finishing fingernails, and
then just polish afterwards.

I’m a big proponent of using the least toxic and caustic methods
possible. Nitric acid is not for home studios, and should only be
used by those trained in chemical lab procedures and have a full
setup for containment and safety (eye wash station, dump shower,
closed disposal system). Switch to ferric nitrate, and you’ll be glad
you did. Besides being more controllable, less caustic, you will have
better results with cleaner etch and a deeper etch, although
considerably slower.

Hi Linda,

For removing the resist after etching, instead of using nail polish
remover try using acetone (it’s the main ingredant in remover
anyways) and a shop towel (the soft blue kind). Both of these thing
your can probably find at the hardware store. This may make it at
least a little easier on the hand and arm.

Zoe Hardisty

Hi Linda,

Your nitric bath might need a touch up. Couple of questions:

  1. is your nitric bath sitting open to the air?

  2. do you pour your solution back into an empty glass bottle and cap
    it off?

If you answered yes to the first question, then I suggest storing it
in a closed glass container.

If you answered no, then I would ask, what kind of water are you
diluting your acid. Regular tap water has all kinds of weird things
in it these days.

To get consistent results, I would do the following.

  1. Remix a new solution with fresh nitric and de-ionized water. This
    is not the same as distilled, but close. You can use distilled just
    fine, but de-ionized is better. Depending on where you live, a
    university or bio science firm can give you a gallon for free. Tell
    them what you are using it for and they often can give you friendly
    suggestions. You might even make a sale of your jewelry!

  2. Make sure of course that your solution is stored in a closed
    glass container. Again, a university or bio science company could
    give you a clean glass container from one of their chemicals,
    provided it is scrupulously clean!!! If they cannot, order one from a
    biological supply catalog, Fisher, Perkin Elmer, they are all online
    anyway.

  3. Forget nitric and use ferric nitrate instead. Works great, just
    slow.

  4. Removing PnP blue. Finger nail polish removal is fine, which in
    its pure state is just diluted acetone. Get a quart of pure acetone
    from the hardware store. It’s handy stuff to have around anyway. PnP
    blue is plastic and acetone will eat some kinds of plastic. Do a
    little test first. The other is just burning it off. It’s just
    plastic, and should burn away with very little heat.

I cannot stress enough regarding ventilation, safety glasses, etc.,
when you are working with acids, but you probably know this already.
Think of me as the flight attendant on your 62nd airplane ride. You
know the stuff, but its good to locate the exit doors in case of an
emergency.

Lastly, when you are performing tasks of this nature, you have to
get out of the “I’m an artist” mindset and think of yourself as a lab
tech. You are absolutely correct to post this to the group. I can’t
tell you how many times with my students, that it is one thing to
design a piece of jewelry for which your artistic merits sing, but
once you do, you need to switch modes and become a mechanic,
scientist, metallurgist, etc.

Deconstructing your designs and figuring out the order everything
must be built is what makes well crafted work. What makes you the
artist is the accident in between and working towards making them a
feature.

Good luck. Write again if you have questions.

-k

Karen Christians
M E T A L W E R X
50 Guinan St.
Waltham, MA 02451
Ph. 781/891-3854 Fax 3857
http://www.metalwerx.com/
Jewelry/Metalarts School & Cooperative Studio

Hi, Linda,

It’s unlikely that your solution is spent aleady. Yes, temperature
makes a difference, but nitric should work fine even cool, and will
still work after it turns a pretty intense blue. Could there have
been any kind of residue on your silver last time? My favorite
solvent for after etching is laquer thinner-- it is a mixture of
solvents, and will dissolve almost anything.

–Noel

is my solution simply spent? 

You may need to spike your solution with some more nitric acid,
especially if you’ve been etching with it for a few months or it
hasn’t been in a fully airtight container.

Does the temperature make a difference? 

Temperature is definitely a factor. If you drop a little scrap
silver in there for at least a few minutes before you start etching
it will get the acid bath warmed up for you. You can take the silver
scrap out or leave it in until you are done using the bath, but the
longer you leave it in, the quicker your acid bath will weaken. This
should definitely give you more consistent results.

The second day I saw a lot more bubbles, but with the exception of
one side of one piece, did not get a deep etch at all. 

For more consistent results you must also brush off your plate
constantly with a soft brush or a goose feather. Bubbles collect on
the surface of the plate and sometimes stay on your lines or
patterns and prohibit the acid from reaching those areas. Unless
you’re etching in a stand up bath, you should not be etching both
sides of the plate at the same time because bubbles will just
collect on the underside and stay there. For my fine line etchings,
I brush the plate every 30 sec - 1 minute but with a respirator on.

hope this helps
kerri

Hi Kerri -

I’ve been trying to find a respirator that works with nitric acid.
What are you using?

I have a question about this:

Temperature is definitely a factor. If you drop a little scrap
silver in there for at least a few minutes before you start
etching it will get the acid bath warmed up for you. You can take
the silver scrap out or leave it in until you are done using the
bath, but the longer you leave it in, the quicker your acid bath
will weaken. This should definitely give you more consistent
results. 

How does putting scrap silver into the acid change the temperature,
and how does weakening the acid give more consistent results? Both
of those things sound counter-intuitive to me.

Thanks!
Linda

For more consistent results you must also brush off your plate
constantly with a soft brush or a goose feather. [snip] For my
fine line etchings, I brush the plate every 30 sec - 1 minute but
with a respirator on. 

For what it’s worth, if you etch a lot, want smooth results, and
don’t want to stand there…

The “standard” technique is to tape an aquarium pump to the side of
the container so that the vibration will dislodge bubbles. A step
better, in my opinion, is to shoot the air stream from the pump
alond the side of the bath to stir it. Best yet is to use a
chemist’s tool, a magnetic stirrer. It consists of a box with a
rheostat and a top surface on which you set your bath. Under that
surface is a magnet that spins at adjustable speed. You drop a
plastic-covered magnet, shaped like a vitamin capsule, into the
bath. It spins, keeping the liquid moving; hence, no bubbles. Plus,
this really speeds up the etch, a good thing when using ferric.

One caution, however-- the bath must be pretty deep, and the metal
held up off the bottom. If the bath is shallow, you will get swirl
lines etched into the metal from the motion of the liquid. This can
actually look kinda cool, but if you want smooth…

I bought my stirrer cheap (used) on eBay, I think about $15 (they
are quite expensive new). If you luck out, you can find one with a
burner, and keep the bath warm at the same time (for ferric, not
nitric acid!) though these can cost more and are less common.

HTH!
Noel

Noel and others,

Please note, the technique Noel is talking about is for FERRIC
NITRATE, not NITRIC ACID.

I agree with the magnetic stirrer option if you can find the right
equipment. The aquarium pump on the outside is not to dislodge
bubbles, but rather to speed the etching process by keeping the
liquid moving against the metal and helping to dislodge the loosened
particles faster. I wouldn’t recommend having the air stream shoot
the air bubbles in the tank, because you can cause a mini tornado
effect and have the etch in only one area.

-k

Karen Christians
M E T A L W E R X
50 Guinan St.
Waltham, MA 02451
Ph. 781/891-3854 Fax 3857
http://www.metalwerx.com/
Jewelry/Metalarts School & Cooperative Studio

Kerri -

Thanik you for the about the respirator and how the raw
silver works.

I purchased an AOSafety respirator at my local hardware store but
couldn’t find any about whether or not it worked with
nitric acid on the box or on their Web site. So I called them and
they told me that it wasn’t possible to make a respirator that
worked with nitric acid because the cartridges use charcoal and
there was no way to get the nitric molecules to attach to the
charcoal. So now I’m wondering whether the person I talked to knew
what they were talking about. Does the package of your respirator
say that it’s for nitric acid?

Linda

Karen,

Noel does explicitly state that his tip is for “for ferric, not
nitric acid!” As for the airbubbles in the liquid my past experiences
led me to understand that the air was distributed by a tube with
many orifices evenly distributed along the bottom of the tank. A
submersible heater can also be used.

Actually, the described setup is commersially available. It is used
for etching copper for printed circuitboards. The choise of etchant
decides which temperature to use. Most acidbaths generates their own
heat and doesn’t need heating although many years ago I used a
sulfuric acid bath to etch copper and that was heated to 100 degrees
to be active, but is was very even in etching (it contained 25
gallons liquid), important for me since my requirements were
measured in 0.02 mm.

If you feel your etchant gets spent too fast, get a larger bath. And
preferably deeper. Etching in a pan or shallow bowl isn’t the best
way although i surely works for many.

kindly
michaela

Micheala,

Thanks for pointing this out. Noel is usually very good about these
things, and I think I just deleted the topic before I posted.

I am aware of the kind of etching system that PCB’s use, but I
wanted to get away from having to remove any additional apparatus in
and out of the bath. When I first posted the etching protocol, I
received an email from somebody who put the fish aerating pump in the
acid bath and was wondering why it was smoking! Geez, I’m glad this
person didn’t electrocute themselves!

My etching protocol is meant for anyone to perform this simply
anywhere. It’s good for rollerprinting, printmaking, etc. Simple
works best for me and for my students.

Thanks for the info though. I would be happy to hear your process as
I am sure others would too. That’s what makes this forum so useful.

-k

Karen Christians
M E T A L W E R X
50 Guinan St.
Waltham, MA 02451
Ph. 781/891-3854 Fax 3857
http://www.metalwerx.com/
Jewelry/Metalarts School & Cooperative Studio

I purchased an AOSafety respirator at my local hardware store but
couldn't find any about whether or not it worked with
nitric acid on the box or on their Web site. So I called them and
they told me that it wasn't possible to make a respirator that
worked with nitric acid because the cartridges use charcoal and
there was no way to get the nitric molecules to attach to the
charcoal. So now I'm wondering whether the person I talked to knew
what they were talking about. Does the package of your respirator
say that it's for nitric acid?

After doing some research, they don’t make a mask for this type of
nitric acid usage, but you should be using the bath under a hood or
with very good ventilation. For higher concentrations of nitric
acid, they tell you to use a self-contained breathing apparatus. But
if you are working under a ventilation hood you should be fine. I
usually don’t breath when I’m putting my plate in and out of the
bath. And I try not to look in the bath because it irritates the
eyes. This info came from MSDS sheets, NIOSH, and 3M. The package of
my respirator cartridges (with P100 filter) actually does cover
other acids but not nitric.

I was told wrong years ago in school, but luckily I have taken every
other precaution when it comes to nitric acid. Sorry about the
confusion.

I have requested to take off my last post so no one else makes my
mistake.

kerri