Etching stone

[Silver_Artisans]

Can anyone tell me what acid etches stone, and the required strength? I am interested in etching Sodalite, Onyx, and other stones.

Do you have to change the acid strength and/or the type of acid used depending on the type of stone etched?

Jon Olson

[Tim_Goldstein]

Jon,

We do stone etching mechanically instead of chemically. We put on a
mask made from sign making vinyl (we actually cut it on a sign
machine) and then sand blast it with a very fine 240 grit silicon
carbide grit. It cuts the stone pretty rapidly and leaves a very
sharp line without any undercutting. The blasted surface has a very
fine matte finish.

Tim
A2Z Metalsmith Supply Inc
5151 S Federal Blvd Unit I-9
Littleton CO 80123
720 283-7200 Phone
720 385-2118 Fax
www.A2ZMetalsmithSupply.com

[Ron_Charlotte1]

Historically, strong alkali solutions were used to etch Cornelian,
so I assume much the same would apply to similar types of stones.
You'd probably have to play with the strength. I'm sure that the
kinds of acids that etch glass will probably do the job as well.

Ron Charlotte -- Gainesville, FL
@Ron_Charlotte1 OR afn03234@afn.org

[Roseann_Hanson]

Jon,

If you are just looking for surface (light) etching to give the
stones a frosted appearance, you could try Etch All -- available at
beadwork suppliers and I believe Rio Grande, though I didn't check.
Fire Mountain Gems had it. I've not tried it yet but wanted to
experiment with painting on a resist in a pattern (like petroglyphs
or something) and see if I could get anything in similar stones.

Will be curious what others have to say!

Roseann

[Steelybone]

Different stones will be etched by different chemicals. Carbonates
(calcite, rhodochrosite, malachite, mexican onyx) will be etched by
hydrochloric acid (HCl). Not a very nice liquid. Silicates
(including all the quartzes, feldspars, chacedonies, jaspers, and
sodalite, among others) are etched by hydrofluoric acid (HF). HF is
a truly nasty acid that can blind you, kill you, dissolve your
bones, upset your calcium balance and mess up your heart chemistry,
take off your fingernails, etc. I don't recommend using it unless
you really know your lab procedure, and since you asked, chances are
you don't. Please stay away from it. The etchants sold in craft
stores are frequently based on weak HF - be very careful of those
too.

Tas
http://www.earthlywealth.com

[John_Burgess2]

Can anyone tell me what acid etches stone, and the required strength?
I am interested in etching Sodalite, Onyx, and other stones.

G'day; Any stone that is composed or contains silica (SiO2,
quartz) or any of the corundums (ruby, sapphire) will need
hydrofluoric acid, (HF) or at least sodium fluoride and sulphuric
acid (which when warmed, gives HF + sodium sulphate.) But the
process is quite slow. Onyx, chalcedony, agates, jasper, etc need
HF to etch them. However HF is one of the most dangerous of all
acids; great care and complete understanding is essential with
it's use. Any stone containing a carbonate (limestone, marble, Blue
John, calcite etc) is soluble in almost any acid, even sodium
bisulphate. People like stonemasons etch granite, etc using
diamond tools in an CAD driven engraving machine, and some engravers
will even use this method to engrave a picture into hard stone,
relatively inexpensively.
Cheers for now,
JohnB of Mapua, Nelson NZ

[Steelybone]

The etchants sold in craft stores are frequently based on weak HF
- be very careful of those too.

Let me elaborate a little on this point. The craft-store etchants are usually designed for etching glass, which is a silicate, and therefore will work to at least some extent on silicate minerals. You specifically mentioned sodalite - while it's a feldspathoid and therefore a silicate, is is "silica poor", and I don't know how well the standard glass-etchers would work. Granite is a rock made of a mixture of mostly silicate minerals, so the etchant would probably work, but the minerals are of different compositions and would dissolve differentially, giving you a bumpy surface and perhaps messing up whatever you've used as a resist.

John - you sound like you've had a bit of experience with the stuff. I fully agree with you! And I never knew HF would etch aluminum oxide (corundum).

Tas
http://www.earthlywealth.com

[LenandJudy1]

Historically, strong alkali solutions were used to etch Cornelian,
For details on making etched carnelian beads, see the article in
Ornament magazine 4/3 (1980) p. 24ff., and its bibliography.

Judy Bjorkmano

[Steelybone]

Historically, strong alkali solutions were used to etch Cornelian

I knew that strong alkalis would cloud glass, but I never knew
they'd actually etch a silicate within somebody's lifetime. Cool!

Tas
http://www.earthlywealth.com

[Jesse_Brennan]

You can find about these etching chemicals used in
making printed circuit boards here and download MSDS sheets for
each chemical:

ferric chloride: http://www.mgchemicals.com/products/415.html

A. Stated as providing a more consistent etch than Ammonium Persulfate
B. Stated as etching twice as fast than Ammonium Persulfate
C. Roughly 10-20 minute etching time.
D. Will not remove most etch resist inks.

ammonium persulfate:

A. Translucent liquid allows the user to see the progress of the 
    etching process.
B. Roughly 30 minute etching time.
C. May remove some etch resist inks. Must use a compatible etch resist pen.
    http://www.mgchemicals.com/products/410.html

sodium persulfate:

A. Flash point at 180 deg F. FLAMMABLE!
B. The solution is shock sensitive
C. Solution decomposes when heated.
D. Cleaner solution, allows increased visibility during etching.
E. Will not remove most etch resist ink.
F. Must be stored in a ventilated container due to gasseous nature.
    http://www.mgchemicals.com/products/4101.html

Ferric chloride is cheapest- It is a byproduct of steel making (
spent pickle acid) it is a common coagulant used in municipal water
purification both for waste treatment and potable water.

for more see:

http://www.pvschemicals.com/techMSDS/PotableTech.doc

For more on etching mordants see from printmaking
sites: galvanic etching

http://perso.club-internet.fr/gravert/galvetch/contfram.htm

and

Edenburg etch ;
http://www.polymetaal.nl/beguin/mape/edinburgh_etch.htm

jesse

[Michael_Honeycutt]

Hi folks, I'm jumping in here without a complete knowledge of
etching stone, but I have a warning. In the semiconductor industry a
whole lot of silicon etching is done with Hydroflouric acid (HF).
This stuff is big time nasty business. Our safety training courses
gave a detailed description of what can happen to you if you get HF
on you. It can cause a numbness due to nerve damage in the exposed
area that may cause you to not feel the stuff working on your skin.
The HF will be absorbed through the skin and underlying tissues till
it makes it's way to your bones where it starts eating all the
calcium it can handle, basically a chemically induced osteoporosis.
This must be treated with calcium injections directly into the bones
which is extremely painful. Even slight exposure was to be
immediately treated by 15 minutes in a cold shower (50 *F, to dilute
the acid and cold to slow burning ability of the acid), buck naked.
Modesty took a serious hike, all clothing was removed and disposed
of in a manner consistant with extreme hazardous waste, and you
stood there in that freezing water with God and everyone looking on.
Then tests were performed to check the acidity in the exposed region
and, if needed, the shower was resumed until neutralizing agents
could be applied. All in all it was considered a MAJOR deal even if
the exposure was very minor. A good friend of mine got the entire
shower treatment (no calcium injections though) because of a spot on
her backside no larger that 1 1/2".

HF can be safely used but you absolutely must use all the acid
safety gear and you must be totally focused on the task at hand.
Now, this was a concentrated form of HF, heated to near boiling.
Just the same though, there can be serious side effects from HF
exposure. If you choose to use it be extremely careful. It has been
my experience that kits for etching frequently are woefully lacking
in safe handling instructions or instructions for chemical disposal.
Do your homework on the chemicals at hands before you even open the
containers. Learn safe chemical handling techniques and use them.
Even modest exposure to some chemicals can literally change your
life forever and you simply cannot be too careful. OK, sermon's
over. I just thought that, if the Intel corp. thought this stuff was
that dangerous, you deserve a warning as well.

Mike