Problem with nitric acid etching fine silver

I diluted to 25% with distilled water using Helen Hill's formula
(search the archives). 

Whoop, whoop - someone at least listened to me! I had a lot of stick
(offline) at the time, but the formula DOES work - I used it
virtually every day during my chemistry degree - and it’s extremely
useful for many applications.

I also mix mine to 25%, and it works well (my starting concentration
is 38%). I think that perhaps what you’re starting with is not the
concentration it claims to be - as suggested by someone else. I
originally tried diluting my acid to 10%, but it did nothing
whatsoever. I guess it would have done something eventually, but it
would have destroyed the resist well before that.

Helen Hill
UK

The easy way to remember Acid into Water is alphabetical order…
Acid Water

or

Acid
|
|
|/
Water

jay

Alicia, Nitric acid does not work well on copper. Use it only on
silver. Use ferric chloride on copper. Furthermore, is is much
cheaper and safer to use ferric nitrate instead of nitric acid.

Cheers, Don in SOFL.

When you add acid to water at a ratio of 1 acid to 2 water you get
about a 25% concentration of acid. I use this for general etching of
silver to eat away the metal for enamelling. It works fairly fast
without leaving too coarse a finish. If I wanted to do finer work I
use a 5-10% solution. I wouldnt recommend heating the acid, just
allow a longer time. Nitric acid oxidises any organic material very
readily so hot conc acid contacting wood, flesh etc will ignite
spontaneously. When doing school chemistry we used to take a few
wood shavings off the bench and put them in a stainless dish and add
a drop of conc nitric. We would then light the gas in the bunsen
burners from this and had to do so very quickly before all the wood
was converted to a carbonaceous mush. One could just as easily light
the gas from a burning fellow pupil if they were careless with the
acid (we wore wool blazers and they went up a treat).

Best regards,
Nick

When you add acid to water at a ratio of 1 acid to 2 water you get
about a 25% concentration of acid. 

You simply cannot say that. I don’t mean to sound irate, but I’ve
said this until I’m blue in the face, and posted the formula to
calculate desired concentrations, etc. Yet folks still post comments
such as “mix 1 acid to 2 water to get x% concentration”. IT DEPENDS
ON WHAT CONCENTRATION ACID (or whatever) YOU’RE USING! Acids are
available for purchase in different concentrations. 1:2 conc. nitric
to water will give a very different final concentration to 1:2 of
38% nitric acid (concentration I use) to water, for example. It
matters - some might say it doesn’t, but it does - if your acid
varies greatly in concentration to the poster’s acid, and we usually
don’t know, because nobody ever says what they’re using. Is it a
particular problem in the States? Are companies selling bottles of
acid and not specifying the concentration? If that’s the case, then
it’s very poor practice indeed.

I’m not going to harp on about it once again (apart from the fact
that I already have), but if anyone’s really interested in the
formula and instructions on how to use it, I’ll write it yet again
and email it to you offline. I must save it on my computer for the
next time someone says the above.

BTW, I’m not being personal, or singling out the quoted poster.

Helen
UK

As far as adding what to what first, remember that it’s the Acid
that has the “type A” personality and should be added to the
mellowing agent a little at a time.

Ray Brown

One could just as easily light the gas from a burning fellow
pupilif they were careless with the acid (we wore wool blazers and
they went up a treat). 

Sounds like big fun : -). You are right, even a 5 - 10 % solution
will work, but I like the coarse finish you can obtain with a strong
solution - only nitric seems to be capable of doing this. You can
speed up the action by heating it in a pan with a lid, until brown
fumes form - keep the lid on the pan and put it somewhere outside for
a while. It’s not a good idea to breathe this fumes, but they will
not kill you (and they do not form nitric acid in your lungs, as
someone said). I do not have access to ferric chloride and I tried
etching steel with nitric, but it does not work - sulphuric acid does
not work either (a 95 % solution ate through my ceramic dish of 3 mm
in 2 days, but no effect on the steel). In my opinion, sulphuric acid
is far more dangerous in every respect than nitric acid, the
exothermic reaction is amazing (it makes cold water boil in a matter
of seconds) and breathing the fumes will form sulphuric acidin the
lungs.

Best regards,
Alicia

As folks who’ve read my posts know, I’m often the first to jump in
when people ignorantly and unnecessarily spread panic about
chemicals, but I’m not just a cynic, I like to operate from facts.
And this one scares me.

You can speed up the action by heating it in a pan with a lid,
until brown fumes form - keep the lid on the pan and put it
somewhere outside for a while. It's not a good idea to breathe this
fumes, but they will not kill you 

Don’t bet your life on it. The brown fumes are the dioxide.
http://msds.chem.ox.ac.uk/NI/nitrogen_dioxide.html

An excerpt: “Highly toxic by inhalation. Inhalation may be fatal.
Corrosive - causes burns. Severe respiratory irritant. Typical PEL 5
ppm.”

they do not form nitric acid in your lungs, as someone said 

You should read this, also:

“The primary locus of NO2 toxicity is the lung. Exposure to NO2
induces pulmonary injury in a number of ways. NO2 is converted to
NO, HNO3 (nitric acid), and HNO2 (nitrous acid) in the distal
airways, where it exerts direct toxic effects on type I pneumocytes
and ciliated airway cells. NO2 initiates free radical generation in
the terminal bronchioles, resulting in protein oxidation, lipid
peroxidation, and subsequent cell membrane damage. NO2 also alters
macrophage and immune function, causing impaired resistance to
infection.”

Al Balmer
Sun City, AZ

You can speed up the action by heating it in a pan with a lid,
until brown fumes form - keep the lid on the pan and put it
somewhere outside for a while. It's not a good idea to breathe this
fumes, but they will not kill you (and they do not form nitric acid
in your lungs, as someone said). 

What on earth makes you think it won’t form nitric acid in your
lungs?! You’re heating nitric in a pan until brown fumes form, ie.
making a very concentrated, fuming nitric acid. Breathe that in, and
it will mix with the moisture in your lungs - and it WILL STILL BE
NITRIC ACID, which is extremely corrosive to organic matter. This I
know from painful experience, from getting a nasty nitric burn on my
thumb knuckle - it took months to heal and has a horrible scar. I
wouldn’t fancy that inside my lungs!

Be careful what advice you give on a public forum. There are lots of
new folk who might now think it’s perfectly okay to heat nitric acid
in a pan - it’s NOT.

Helen
UK

Hi Helen, Al, Al, I share your concern. A lot of dumb stuff is being
told about chemicals. As I said, you can speed up the action of
nitric acid by heating it up in a pan with a lid. You are not
supposed to take the lid off! Who in her right mind would do such a
thing? Once the solution is boiling, put it outside, keep away from
it and let it cool. Pretty harmless, in my opinion. As for the
second point, many years ago there was a discussion going on between
goldsmiths about the health hazards of pickle. I looked up at couple
of articles at that time and, if memory serves me well, I found out
that fumes of sodium bisulphate form sulphuric acid in the lungs
andthat NO2 does not convert to HNO3 because it is too hydroscopic.
But maybe I am just wrong about that. Anyway, this discussion was
about Sparex pickle which many people use warm, but of which I am
certain that it is downright carcinogenic for the reason stated
above, although this is still not recognised in the msds for Sparex
2 (There is no doubt that nitric acid and nitrogen dioxide are
dangerous compounds, so use common sense. I use nitric acid a lot
and I never got burned, though my hands got blackened on several
occasions (which does not hurt). I never inhaled NO2 in whatever
concentration although I boil nitric acid quite a bit. I use
sulphuric acid as a cold pickle from time to time and I never had an
accident with that either.

Best,
Alicia

I share your concern. A lot of dumb stuff is being told about
chemicals. As I said, you can speed up the action of nitric acid by
heating it up in a pan with a lid. You are not supposed to take the
lid off! 

You said, specifically, " It’s not a good idea to breathe this
fumes, but they will not kill you (and they do not form nitric acid
in your lungs, as someone said)"

You are wrong on both counts.

[snip] andthat NO2 does not convert to HNO3 because it is too
hydroscopic. 

That’s precisely the reason why it does form HNO3, by dissolving
in water. I hope you at least read the link I supplied.

But maybe I am just wrong about that. Anyway, this discussion was
about Sparex pickle which many people use warm, but of which I am
certain that it is downright carcinogenic for the reason stated
above, although this is still not recognised in the msds for
Sparex 

That’s because it’s not carcinogenic. Neither is sulfuric acid.
However, it can be dangerous, since it breaks down into SO2 and SO3
at 104 C (far hotter than anyone’s pickle pot.) It also forms SO2 in
contact with acid. SO2 in water is sulfurous acid, SO3 forms
sulfuric.

Al Balmer
Sun City, AZ

... A lot of dumb stuff is being told about chemicals. 

Yup. But take care not to do so as well. Check facts with more than
orchid archives. Lots of people knowing lots of stuff, but in
essence, it’s back fence gossip. Check with actual researched or
verifiable source before assuming chemical facts on Orchid are indeed
such…

As I said, you can speed up the action of nitric acid by heating it
up in a pan with a lid. You are not supposed to take the lid off! 

Heating Nitric, or for that matter, other strong acids, needs more
than a lid. Just as steam comes out from under the lid of a cooking
pot, acid fumes too can escape from a boiling or very hot pot of
acid. Ventillation is critical. And nitric fumes are nasty indeed.

Who in her right mind would do such a thing? Once the solution is
boiling, put it outside, keep away from it and let it cool. Pretty
harmless, in my opinion. 

Using the term “pretty harmless” in reference to boiling acids in
general, is just setting yourself up to make assumptions and careless
mistakes. It’s never harmless. Only one small slip or mistake away
from dangerous, even when handled properly. The key is careful
meticulous procedure and an attitude of care. Referring to the stuff
as harmless, even if in fact it “CAN” be harmless, is setting
yourself up for a greater chance of error.

As for the second point, many years ago there was a discussion
going on between goldsmiths about the health hazards of pickle. I
looked up at couple of articles at that time and, if memory serves
me well, I found out that fumes of sodium bisulphate form sulphuric
acid in the lungs 

Sodium bisulphate is a salt of sulphuric acid. It doesn’t easily or
substantially break down to gasseous fumes on normal hot pickle use.
There can be a little, but not much. What does happen is that with
any boiling liquid, some of the liquid escapes as tiny aerosol
droplets along with the steam from boiling. The droplets are still
sodium bisulphate, and in the lungs, which means simply mixing with
fluid, it becomes more dilute sodium bisulphate. This does not mean
it’s harmless there. Only that it remains an acid salt of sulphuric
acid, rather than the straight acid itself. This is perhaps a minor
point, since the chemical actions of sodium bisulphate are not
tremendously different from the acid itself, only less potent, and
importantly for pickle use, it does not actually emit acid gas fumes,
as sulphuric acid can do. That is actually the main factor that makes
it markedly safer to use as a pickle than plain sulphuric acid. The
easy fix is both to keep your pickle covered, and to operate it at
below boling temps. That pretty much controls most of the fume
issues with sodium bisulphate pickle. There will be some trace fumes
even so, and some people find themselves sensative to it. For them,
use it cold, or switch to something like citric acid. But compare the
smell of sodium bisulphate pickle, even hot, to that of even cold
sulphuric acid pickle, and you can quickly smell and feel the drastic
reduction in fumes from the sodium bisulphate pickle.

about Sparex pickle which many people use warm, but of which I am
certain that it is downright carcinogenic for the reason stated
above, although this is still not recognised in the msds 

What, pray tell, leads you to think acid fumes, such as from sodium
bisulphate, are carcinogenic? Sulphuric acid burns. It’s pretty
nasty stuff, especially to organic materials (concentrated sulphuric,
spilled on a wood table top, can sometimes even cause it to ignite,
it’s that aggressive an oxidizing agent). but just because something
is toxic or nasty or caustic or acidic does not equate in any way to
being carcinogenic. I’m not saying it’s somehow safer, but lets keep
the risks seperate. Nothing I can find on either sodium bisulphate or
even sulphuric acid itself suggests any sort of carcinogenic
activity. Materials that are carcinogenic are not just ordinary run
of the mill things that cause cell damage, etc. They have to be able
to cause quite specific types of damage that change a cells function
and genetics perhaps, rather than kill it. Acids are pretty good at
killing cells, not just tweaking them a bit to become cancerous down
the road… So then. Carcinogenicity of sodium bisulphate or
sulphuric acid? References please. Not just back fence gossip
suspicions from the Orchid archives.

Peter Rowe

Can we start to differentiate between concentrated Nitric acid and
diluted Nitric acid?

Concentrated forms are usually slightly yellow due to decomposition
of the acid into its oxides. It is an oily, viscous liquid. Copper
reacts with it and forms acrid brown/red fumes. This is the acid
that you add to water to form the dilute forms. It is hydroscopic
(water-greedy) and stains flesh brown.

The varying degrees of dilute acid are, for us, the useful ones. If
you have to boil the acid to etch metal you are using it too dilute.
Boiling the acid will, eventually, give off dangerous fumes of the
pure acid even before the water entirely evaporates and it returns
to its concentrated form.

Tony Konrath

Al, Peter, Sorry, you are both wrong. The Safety Data Sheet from
Sigma-Aldrich on Sulfuric Acid states that:

“The International Agency for Research on Cancer (IARC) has
determined that occupational exposure to strong-inorganic-acid mists
containing sulfuric acid is carcinogenic to humans (group 1)”.

Note that they refer specifically to mists. If you do not believe me,
by all means, send them an e-mail. The sheet goes on:

“Material is extremely destructive to tissue of the mucous membranes
and upper respiratory tract, (.) (causing) inflammation and edema of
the larynx, inflammation and edema of the bronchi, pneumonitis,
pulmonary edema, (.) laryngitis (.). To the best of our knowledge,
the chemical, physical, and toxicological properties (of sulphuric
acid) have not been thoroughly investigated.”

This last sentence is relevant for what follows re. pickle. Sodium
bisulphate (NaHSO3) is a salt of sulphuric acid (H2SO4). It will
form fumes when heated to normal pickle temperatures and I have seen
pickle steaming 10,000 times by now because people use slow cookers,
slowly the pickle gets way too hot. There are two issues here.

First, there is psychological resistance. I have been talking to
goldsmiths about this a lot and many are not going to accept that
they have been treating themselves for the last 40 years to a nice
mist of carcinogenic agent. This is too much for them to come to
grips with, so there is denial.

Second, there is science. Many people believe that there is a divide
between opinion and fact and that that is all what is. However,
science is much more a mirror of interests in society than a mirror
of nature.

The reason why these toxicological effects are not well understood
is that no one seesan interest to investigate into them. I am sure it
is well possible - and perhaps it has been done - to make breathe
some dogs some sulphuric acid and to conclude post mortem that
sulphuric acid is not carcinogenic because no tumours are found,
forgetting to mention that almost no lung tissue can be found either.
You are free to believe such results, it depends on your opinions and
on your interests. The alternative is to set up an epidemiological
survey which will cost many hundreds of thousands of whatever
currency you are using. However, you can use deductive reasoning and
conclude that you cannot come up with any valid chemical reasoning
which will prove that long term exposure to mists of sodium
bisulphate is not carcinogenic.

No one knows exactly how carcinogenic it is. It’s possible that it
is more carcinogenic than sulphuric acid. Or perhaps it is less
carcinogenic. But that it is carcinogenic, there is no doubt. And
this is what you should do if you would be careful, according to
principles of risk assessment, more careful than boiling nitric acid
under a lid. As for references, I will do a search later on, but now
I need to work.

Alicia Webb,

Al, Peter, Sorry, you are both wrong. The Safety Data Sheet from
Sigma-Aldrich on Sulfuric Acid states that: 
The International Agency for Research on Cancer (IARC) has
determined that occupational exposure to strong-inorganic-acid
mists containing sulfuric acid is carcinogenic to humans (group 1) 

Yes but this only applies to mists containing sulfuric acid as
stated in several MSDS not to the acid itself again specifically
noted in several MDSDS’s. To get a mist containing sulfuric acid you
will need to either aerosolize it or bring it to a boil so that it
vaporizes. In the typical studio it is not handled in a way to do
this. Yes it is often heated but sulfuric acids boiling point is
quite high at 554F (290C) so the vapor coming off a pickle solution
is water vapor not acid vapor. I am not trying to minimize the danger
of working with or handling sulfuric acid but in our use cancer is
probably not the danger to be concerned with.

As for sodium bisulfate it is not listed as a carcinogen by the IARC
or any other regulatory agency that is listed in MSDS’s for it, so I
think your reasoning is lacking in a factual basis here.

James Binnion
James Binnion Metal Arts

Alicia,

The “fumes” coming off the surface of hot pickle is water vapor, not
sulfuric acid mist!

There is a tiny amount of the salt in it but no more and no more
dangerous than that which you get when you are making dill pickles.

Scientific interests, it is true, do reflect social interests but
scientific method does not so let’s use it…

Place a sheet of cold glass above the surface of the steaming pickle
until a drop of water is available then test it with a piece of
litmus paper.

See? No acid!

Tony Konrath

There is a tiny amount of the salt in it but no more and no more
dangerous than that which you get when you are making dill
pickles. 

Not if you’re using a sodium bisulphate pickle, it’s not. Dill
pickles, you’ve got acetic acid (vinegar) sodium chloride, (salt),
and perhaps dill, other spices, maybe even alum. All these are safer
to consume than any sulphuric acid salt. And while sodium bisulphate
is not sulphuric acid, but rather a salt thereof, it still can enter
some of the same chemical reactions as the acid, including causing
burns in some situations.

The amount of sodium bisulphate that might be carried out of a
steaming hot pickle pot is very small, as you say. But unlike the
vinegar fumes from making dill pickles, that small amount of sodium
bisulphate is still corrosive enough so if your pickle pot happens to
be near to a plier rack or your nice files, you’ll have some
aggressive rusting to contend with… And if you put your face right
over the pickle pot and breath deep, you’re gonna find its a good
deal nastier and doesn’t smell just like your hot morning shower…

Now, the pickle pot with sodium bisulphate is much safer than a
pickle with sulphuric acid, which does give off really nasty fumes.
Usually, reasonable workshop ventillation that most of us can easily
arrange, a common sense placement of the pickle pot, and keeping it
at least lightly covered, is all the precaution you need to take with
a hot pickle pot. So in this sense, you’re correct. But I’d suggest
that saying this is the same as making dill pickles, might be
understating the issue just a tad.

Peter Rowe

There is a tiny amount of the salt in it but no more and no more
dangerous than that which you get when you are making dill
pickles. 

Please. This belongs to the same category of denial of which Peter
Rowe gave a brilliant example the other day: sulphuric acid may
cause severe burns, it may ignite the wood of a table, it may even
kill a couple of cells, but damaging DNA and causing mutation, well
no. Put a piece of clothe on top of your pickle pot until it is
moist, take it away, put a steel tool on it for a couple of days and
witness the corrosion. If you really need to appreciate the
difference, do the same with dill pickle liquid. Did you ever hear
about acid rain? What do you think it is? It’s sulphuric acid - SO2
becoming SO3 and finally H2SO4 - which attaches itself to small
particles in the air.

As for sodium bisulfate it is not listed as a carcinogen by the
IARC or any other regulatory agency that is listed in MSDS's for
it, so I think your reasoning is lacking in a factual basis here. 

I said so myself that there is no factual basis, I explained why and
I said that using deductive reasoning, you cannot come up with any
valid argumentation explaining that long term exposure to aerosols
of sodium bisulphate is not carcinogenic.

I do not agree with what Jim Binnion is saying about sulphuric acid.
Where do you get the idea that it is necessary for the acid to reach
boiling point to become a mist? Any aerosol is a mist. If you get
sulphuric acid on your skin, it causes a burn. If you breathe in
fumes - vapour - containing sulphuric acid it will be corrosive to
your lung tissue, just as it is corrosive to your teeth and to any
other internal tissue. That is what the categorisation by the IARC
means. It has nothing to do with boiling whatsoever. It’s well known
that people living nearby waste sites which contain sulphuric acid
are at greater risk of exposure by breathing contaminated air than
others and workers who are exposed to sulphuric acid run greater
risk of getting cancer of the larynx than other people. Aside from
being corrosive in itself, sulphuric acid decreases the ability of
the respiratory tract to remove particles. It’s especially
problematic for children, because their airways are smaller and
because they breathe more air per kg of body weight than adults.

Long term occupational exposure to sulphuric acid mist is
carcinogenic. There is no reason to think that the same exposure to
mist of sodium bisulphate is not carcinogenic. The fact that it has
not been tested does not prove that it is not carcinogenic. Given
the similarities between sodium bisulphate and sulphuric acid - they
are identical except for one Na atom instead of one O atom and it
has one H atom less than H2SO4 - the only intelligent thing to do is
to base one’s actions on the precautionary principle - treating the
stuff as if it is carcinogenic as long as it is not proven
otherwise. If you use sodium bisulphate as a pickle, give up the
denial about it, do not let it boil and if you use sulphuric acid,
use it cold only. While one can smell nitric acid for example from
far away, the odour threshold of sulphuric acid is remarkably low.
Do not assume that it is not there because you do not smell it.

Lastly, I do not understand why Hanuman removed my title behind my
name in my previous post.

Leach Webb, PhD.

This really takes the biscuit…

Please. This belongs to the same category of denial of which Peter
Rowe gave a brilliant example the other day: sulphuric acid may
cause severe burns, it may ignite the wood of a table, it may even
kill a couple of cells, but damaging DNA and causing mutation,
well no. 

We were talking about safety pickle. This is the bisulfate. The
steam coming off the pickle pot will contain almost none of the
salt.

Put a piece of clothe on top of your pickle pot until it is moist,
take it away, put a steel tool on it for a couple of days and
witness the corrosion. 

This will happen with any damp cloth!

If you really need to appreciate the difference, do the same with
dill pickle liquid. Did you ever hear about acid rain? What do you
think it is? It's sulphuric acid - SO2 becoming SO3 and finally
H2SO4 - which attaches itself to small particles in the air. 

That’s not the process of acid rain damage!

Tony Konrath

I said so myself that there is no factual basis, I explained why
and I said that using deductive reasoning, you cannot come up with
any valid argumentation explaining that long term exposure to
aerosols of sodium bisulphate is not carcinogenic. 

If a person wants to go looking for reasons to be afraid, they will
find plenty in jewelry making. Knowing how to handle chemicals and
what they are about, and risk assessment, is all part of the package

  • essential knowlege, infact. Saying
they are identical except for one Na atom instead of one O atom
and it has one H atom less than H2SO4" 

betrays a complete lack of understanding of it all, I’m afraid. A cat
is identical to a dog except that one’s a cat and one’s a
dog…

Put a lid on your pickle pot, put it by a window or something, and
go home and sleep nights. Jo-Ann said this morning, “Jeez, it still
hurts where I put the cup bur into my finger…” The polishing
machine is 1000 times more dangerous than your pickle pot is. Be an
accountant, unless a paper cut makes you faint…