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Remove Vitreous Enamel?


#1

Anyone know how to remove colored vitreous (glass) enamel on a $5
indian head coin?

Sterling J VanDerwerker CGA (AGS) GG (GIA)
Royal Diadem Jewelers


#2

Sterling

Soak the item in Hydrofloric acid. It dissolves glass but does not
touch metal. Therefore the acid is housed in plastic containers.

Cheers.
Kim
www.kimericlilot.com


#3

The only non-destructive way that comes to mind is thermal shock,
heat the coin to 300 to 400’F (might be higher if depends on the
enamel) and quench in iced water, the shock should remove most of the
enamel, the rest should come off with hammer type setting tool (for a
flex shaft) with a chisel like point, if you can rig up something
along those lines. You will mar the coin somewhat unless you are
extremely careful with the chisel.

The heating will also remove any patina that was present, and if you
over heat you run the risk of producing fire scale too. So go slow
and try it a various temps working your way up til the stuff moves.

Good luck.
Cheers, Thomas.
Janstrom Designs.


#4

Hi Sterling,

In her book Enameling on Metal Clay, Pam East recommends mixing
equal parts salt and cream of tartar then add just enough water to
make a creamy paste. Apply it to the offensive enamel and re heat to
fusing temperatures for 2-4 minutes. Quench and use tweezers and a
stiff wire brush to remove the burnt enamel.

She credits this technique to Gilberto Mazzotti.

Lora


#5

Hi Sterling,

Last time I had to remove vitreous enamel I etched it off with liquid
etchant (I think I used Etch-All, but I can’t remember). Anyway, it
took several days and I changed out the liquid about every day
because it was old and not as strong. I was removing it from fine
silver and had no problems. I don’t know what your coin is made of,
but the etchant worked really well for me. Get it at Thompson or
Enamel Works. Heck, Rio probably sells it.

Hope that helps!
Tammy Kirks


#6

Hello Sterling;

Anyone know how to remove colored vitreous (glass) enamel on a $5
indian head coin? 

I’ve had to remove vitreous enamels before, and tried heating and
quenching to thermally shock and shatter the enamel, but the results
are limited. Here’s what I’ve found works. First, heat and quench,
then put it in the ultrasonic (if you have one, otherwise, just go
at it with a brass brush for a bit). Repeat this util you’ve gotten
rid of most of the enamel. Now, heat the article and sprinkle borax
on it. Continue heating until the borax melts. What this does is
dilute the vitreous enamel with a water soluble form of glass. Now,
pickle it for a while, then rinse and repeat. Eventually, you’ll
disolve the enamel in the borax, and the borax will disolve in the
pickle.

David L. Huffman


#7

You can use Etchall creme or liquid. Sometimes JoAnn’s Crafts or
Micheals will have this in stock. I have used this a couple of times
to remove the enamel from fine silver.

Brenda
www.brendaschack.com


#8

Someone I met this summer told me of a method to improve the removal
of enamels.

Mix
1 part table salt
1 part cream of tartar
water to a paste

apply over the enamel
dry it
fire it
then plunge into water

it is supposed to work very well.

best
Charles


#9

Asked my wife, who is an enamelist, she suggested that you could heat
it up to a few hundred degrees (oven baking temperatures) and then
drop it into a bowl of cold water. Much of the enamel would break up
due to the thermal shock. Wear safety glasses. Would probably leave
some behind. There are acids (hydrofluoric for example) that etch
glass and not metal. You could try one but it will take quite a while
to do its thing.

–Steve


#10

Hydrofluoric acid is EXTREMELY dangerous. I used to use it to
dissolve porcelain from metal copings when making dental crowns.
This should be treated with a great deal of respect!

Andy


#11

Warning-- Hydroflouric acid is very hazardous material to handle. A
very small amount can do a lot of damage to your body, an example
being that you can lose fingernails by getting a little HFl on your
hands and not properly washing and neutralizing under the tips of
your nails. Not good for breathing either-- use outside or under a
really good hood with plenty of water.

Jim
Mardon Jewelers
www.mardonjewelers.com


#12
Warning-- Hydroflouric acid is very hazardous material to handle.
A very small amount can do a lot of damage to your body, 

This is something that needs to be said every time the subject comes
up. HF is what you might call “insidiously dangerous”. It doesn’t
seem so bad, like fuming nitric or something. Pour it onto something
and it will just sit there. Pour it on your skin and it won’t hurt
much, at least at first. It’s one of the top three or five
(inorganic) dangers in industry though, for that very reason. Pour an
ounce of nitric acid on your flesh and wash it off immediately and
you’ll have a bad acid burn. Pour an ounce of HF on your flesh and
wash it off immediately and you’ll probably die - not a joke. It is
incompatable with human flesh in any form.

http://www.donivanandmaggiora.com


#13
Pour an ounce of HF on your flesh and wash it off immediately and
you'll probably die - not a joke. It is incompatable with human
flesh in any form. 

And yet, you can buy it, in dilute form, at Michael’s and other
hobby places, in the form of ArmourEtch and EtchAll or some such.
This astonishes me. It is used for etching glass-- I have used it
(wearing nitrile gloves). The preparation I had smelled like
gingerbread. Scary!

Noel


#14

Hydroflouric acid should not be used outside a specially designed
fume hood and with sufficient safety training. A spill that covers
5% of the skin area is normally considered a fatal exposure. There
are some recent treatments that can save the victim if they ER has
the materials on hand and the knowledge to use them but it is still
not something to be used lightly. Those glass etching creams have a
fluoride salt in them and are safer than HF but are still dangerous
and need to be treated with caution as well. Just because they are
sold at craft stores does not make them safe. Make sure that you use
gloves and goggles and be careful when using the creams.

Jim

James Binnion
@James_Binnion
James Binnion Metal Arts


360-756-6550


#15
And yet, you can buy it, in dilute form, at Michael's and other
hobby places, in the form of ArmourEtch and EtchAll or some such.
This astonishes me. 

Not to pound the dead animal, but there are a few links off of the
Wikipedia article on HF. One is a medical study of people who went
to doctors from injuries sustained when using some of the OTC
preparations. They are like 5%-6% HF, usually, and they do real
damage, too. One of the biggest reasons given was, “Didn’t follow
the directions.”

http://www.donivanandmaggiora.com


#16

This is my first message for this group! My name is Priscilla and I’m
a jewelry author, working nowadays mostly with metal clay and silver
alloys. I’ve taken few torch-firing enamelling classes and have made
a few enamelled pieces, some work well, some doesn’t. Sometimes, when
it doesn’t, I just lose the interest in that piece and toss it onto
my “mistakes” drawer (growing fuller every day…), but a few times
I just want that piece to work, so I just remove the enamel and
start over again.

I’d like to share my method of removing enamel; it’s simple, non-
toxic or dangerous, just a bit messy. It is a thermal shock, but you
have to cover the entire enamelled area with a mixture of 50/50 table
salt and cream of tartar, and just enough water to make it “wet-
packable”. Heat it from beneath with a torch until the mixture is
burnt, and you know that the enamel is molten, then drop the piece
upside-down into a bucket full of water. Sometimes you have to repeat
the process, specially in deep areas or when you just don’t heat the
piece enough for the enamel to be molten, but I never had to do it
more than 3 times, and all the enamelis removed that way.

I hope this can be helpful to some of you!

Priscilla Vasseo
Art Clay Brasil
www.artclay.com.br


#17
And yet, you can buy it, in dilute form, at Michael's and other
hobby places, in the form of ArmourEtch and EtchAll or some such.
This astonishes me. It is used for etching glass-- I have used it
(wearing nitrile gloves). The preparation I had smelled like
gingerbread. Scary! 

No what you buy at Michael’s and JoAnn’s is a mixture of fluoride
compounds like sodium bifluoride as well as titanium dioxide and
citric acid as it says in the MSDS. Nasty stuff but not the dreaded
hydrofluoric acid. HOWEVER sodium bifluoride decomposes to hydrogen
fluoride when exposed to acids or heated, hydrogen fluoride and
water which is also in the paste make hydrofluoric acid. Sneaky
bastards don’t tell you this in the MSDS.

Makes you wonder how many folks are poisoning themselves with this
stuff. There are both immediate and chronic effects from working
with it.

Jim

James Binnion
@James_Binnion
James Binnion Metal Arts


360-756-6550


#18

Thanks very much for several methods to remove enamel from a coin.
The silver paste flux and a little stirring with a solder pick above
the surface of the coin worked well. Just a little pickling and
ultrasonic and the coin looks great. Since it was only a fair
condition coin, there was little to loose. I finished off in a pin
polisher for 1 hour and now the coin sits in a rope bezel awaiting a
new home.

Thanks to each one who was willing to help me!

Sterling J VanDerwerker CGA (AGS) GG (GIA)
Royal Diadem Jewelers