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Problem with nitric acid etching fine silver


#1

Hello, I have an insane problem. I am using nitric acid (74-75%) to
etch copper for later enamelling, there is no problem.

Today I put pieces of fine silver in the acid - nothing happens. The
acid does not attack the silver, there is no action and after an hour
the solution turns bleak green, not blue. I put a little piece of
copper in the acid to check if it is okay. It attacks it immediately.
I have no experience with etching fine silver, what am I doing wrong?
I read somewhere about someone putting his fine silver on a sheet of
titanium and sending an electrical current through the acid, but I do
not think that this is necessary. I also read that it is necessary to
dilute the nitric (some say 2 parts of water and one part of nitric,
others mention 3 parts of water and one part of nitric). I poured
some cooking water in the solution (yes, I know), but there is still
no action. What is going on?

Best regards,
Leach


#2
Today I put pieces of fine silver in the acid - nothing happens. 

I’ve had the same problem with sterling. I bought my nitric acid
from a chemical supply house, diluted it to 30% (if memory serves -
the percentage widely recommended, in any event). No amount of time,
nor gentle warming, did anything more than to suggest the hint of an
etch. I’d love to know what is what, too.

Neil A


#3

Hello, This refers to my post of Saturday. After pouring some
boiling water in the nitric acid and seeing that there was still
nothing happening, I went into the house, make a cup of tea and wrote
an e-mail to orchid because I really could not understand what was
going on. When I went back to my studio, the nitric had eaten all the
silver away in the meantime. I did not know that nitric acid (74-75%
solution) by itself does not etch fine silver. I never read this
anywhere. When you add a bit of water to it, it will eat it away
very quickly.

Leach.


#4

Nitric acid is available in two forms, Concentrated (Conc.) and
Diluted (Dil.)

Conc. is an oily liquid that gives of very strong fumes. Copper
dropped into it gives off brown fumes and this is the sort you
dilute.

If you buy Dilute and then dilute it further it will be too weak.

Tony Konrath


#5

Are you sure about the concentration of the original acid? Conc
nitric normally fumes when you open the bottle.

Nick Royall


#6

Hmm,

Where did you source the acid from? Could you say they were reliable?
If so, very conc acids often dont react much as they need the water
to form the H+ ions. Pouring water into your acid should have
produced an immediate and possibly explosive thermal reaction. As you
dont mention it boiling over and setting any organic material it
contacts alight one has to wonder about its dilution. I use 25% acid
(roughly 1 part acid to 2 parts water) The acid should fume when you
open the bottle ( yellow brown smoke) and always add the acid to the
water very slowly and stir whilst doing so. The heat given off can
boil it, hence the care. It etched silver without any difficulty, a
more concentrated solution will etch a little faster but you will get
bubbles sticking to the metal and a rougher surface. Most people use
ferric nitrate for etching copper, this doesnt work so well on
silver.

Nick Royall


#7

I too have once diluted nitric acid with water and it only served to
oxidize the metal, thus creating a resist which impeded the action
of the acid. I think that was the problem!

Dana Evans


#8
Most people use ferric nitrate for etching copper, this doesnt work
so well on silver. 

Rick, Me thinks you may have this backwards. We use ferric chloride
for etching copper and ferric nitrate for silver which normally works
quite well. Cheers from Don in SOFL


#9

You are very lucky you did not end up with a face full of acid.
Never, never, never add water to acid. If you must dilute an
existing solution put the water in a suitable container and add the
acid solution to the water.

For your etching problem, there could be a couple of reasons that it
did not initially dissolve one of which you found out. Diluted acid
solutions can be more effective than concentrated ones in attacking
certain metals. Another possibility is you could have had something
on the silver that was acting as a resist, silver chloride is quite
resistant to nitric acid and can form on silver when exposed to
hydrochloric acid or other chlorine compounds.

Jim

James Binnion
James Binnion Metal Arts


#10
Are you sure about the concentration of the original acid? 

I bought Chemproducts ACS Reagent Grade Nitric Acid 70% from
Malinkrodt Chemicals in Portland Oregon. The assay on the bottle
cites:

Specifications

Appearance Colorless and free from suspended matter or sediment

Assay 68.0-70.0%
Arsenic (As) 0.01 ppm
Chloride (Cl) 0.5 ppm
Color (APHA) 10
Heavy Metals (as Pb) 0.2 ppm
Iron (Fe) 0.2 ppm
Residue After Ignition 5 ppm
Sulfate (SO4) 1 ppm

I diluted to 25% with distilled water using Helen Hill’s formula
(search the archives). Short of doing some kind of chemical analysis
and titrating, I have to assume this is indeed nitric acid and my
dilution is in very close to 25%, as I measured carefully.

It did pretty much nothing overnight except a light frosting and
deterioration of PnP Blue. Prior to leaving it overnight I rocked
the tray, probably gently brushed the metal, warmed the solution…
I also used a large volume of solution relative to the piece I wanted
to etch.

Neil A.


#11
Most people use ferric nitrate for etching copper, this doesnt work
so well on silver. 

I believe you possibly meant ferric chloride for etching copper.
Ferric nitrate does work fairly for etching silver. Ferric chloride
will not due to the formation of silver chloride which acts as a
resist to the action of the acid salt.

Jim

James Binnion
James Binnion Metal Arts


#12
I use 25% acid (roughly 1 part acid to 2 parts water) 

Sorry, this is my bug-bear again. 1 part of what concentration of
acid? Conc. nitric or something between conc. and your 25% final
dilution? I won’t go on about it again here, as I’ve posted about it
countless times, and posted a formula for arriving at whatever
concentration you want, no matter what concentration you start with
(obviously you need to know what you’re starting with).

Most people use ferric nitrate for etching copper, this doesnt work
so well on silver. 

Ferric nitrate works beautifully on silver and it’s what I mostly
use in preference to nitric acid. From what I understand, most people
actually use ferric chloride for etching copper - which doesn’t work
so well on silver. But ferric nitrate works just fine.

Helen
UK


#13
Nitric acid is available in two forms, Concentrated (Conc.) and
Diluted (Dil.) 

It is available in a few different concentrations in the UK.

If you buy Dilute and then dilute it further it will be too weak. 

This is not necessarily true. I buy 38% strength and found that it
was too strong, etching too fast and aggressively. I therefore
dilute it to 25% strength and it works just fine.

Helen
UK


#14

Nick, The solution I used was fresh 74-75 % pure nitric acid from
Scientific and Chemical Laboratory Supplies over here in Ireland. I
think that the solution formed bubbles on the silver, protecting it
from further etching.The nitric needs water to form H+ ions, as you
mentioned, to get to work. Once water is added, the bubbles
disappear and the acid will etch. Probably, a 30 % solution is too
strong to etch fine silver and a weaker solution is even better. I
say this because when I put copper in a 30 % solution the acid bites
it apart in no time, although copper needs more nitric acid than
silver in order to disolve (almost 3 times as much). The fumes are
indeed a problem, esp. when you boil the nitric. But OK, the work is
done now and next time better.

Alicia


#15

Neil, PNP will not hold up with nitric acid. For etching silver using
PNP as my resist, I use Ferric Nitrate and have complete success.

Alma


#16

NEVER POUR WATER INTO ACID!!! Always the other way around, acid into
water. You got lucky this time. Don’t push it.

Also, nitric acid is very dangerous stuff. If you should find that
you nitric acid turned red/orange, be careful. IF NITRIC ACID STARTS
TO EMIT RED/ORANGE FUMES - GET OUT OF THERE AND DON’T BREATH IT IN.
Those fumes combine with the H2O in your lungs to make nitric acid.
Not a pleasant way to die.

Fred Reese


#17

Hello Alicia,

Yikes!

I’m no expert (my usual disclaimer) BUT I think it is generally the
First Rule of mixing water with acid (or many other reactive
chemicals) that you NEVER add water to acid - because if there is a
heat-producing reaction you have the possibility of a sudden boil-up
or even a steam explosion with acid scattered all about. This is
because you have put a relatively small amount of water into a
relatively large volume of reactant. The reaction can heat that
small amount of water very quickly. If you add the acid to the
water, however, the small volume of acid relative to the large
volume of water means that there is enough water to absorb and
dissipate any heat produced so the temperature rises much more
slowly. Add only a bit at a time.

As acids go, I don’t know how nitric acid in particular behaves with
regard to reacting with water - but, for that very reason, I would
not have added the water to the acid but done it the other way round

  • acid into water. Even so - I don’t like guessing at things like
    this.

You’ll probably get other messages of this same sort. There is more
to handling chemicals than just mixing things to see what happens.
Take the time to get some education while you still have your eyes
in working condition.

Marty in Victoria BC


#18

Let’s remind ourselves of the lab technicians addage:

AAA - Always Add Acid

Never add wate to acid, particularly if it’s boiling water.


#19

A quick whiff of the red/brown fumes of Nitrogen dioxide is nasty
but will it not kill you! I had many at school in analytic
chemistry.

Let’s quote from Wiki

“Nitrogen dioxide is toxic by inhalation, but this can be avoided as
the material is acrid and easily detectable by smell.”

Tony Konrath


#20
You are very lucky you did not end up with a face full of acid.
Never, never, never add water to acid. (...) Diluted acid
solutions can be more effective than concentrated ones in
attacking certain metals.

Hi Jim, Yes, I know, but I did this hundreds of times already. I know
how much I can add and it makes a difference whether the water is
cold or hot. Adding cold water to a mildly warm bath of nitric is
dangerous but adding boiling water to mildly warm nitric acid does
not produce any spitting. But OK, the rule should be add acid to
water. I think that a 20 - 25 % percent solution works very well on
fine silver as well as on copper. I do not see any reason to work
with a stronger solution.

Cheers, Alicia