[TheForge] removing silver from a mirror

[Bruce Freeman]

Terry,

I have no experience removing silver from a mirror, but I am a
chemist, so this is my take:

"Aqua regia" is the only acid (mixture) that will dissove gold, so it
will easily dissove silver. It consists of nitric acid with some
amount of hydrochloric acid present.

Silver should be easier to dissove than that. Nitric should work. 
Hydrochoric is not going to work - it won't dissove copper, even,
which is in the same group (on the periodic table). Nitric is an
oxidizing
acid.

However, the neat thing about strong acids is that it doesn't matter
where the anion comes from. So you could take sulfuric acid and add,
say, potassium nitrate and you'd have, in effect, nitric acid (albeit,
not concentrated nitric acid). 

Be VERY careful whenever you mix ANYTHING with strong acid. Violent
reactions can occur. Work in glass containers. Wear eye and hand
protection, in addition to clothes you don't mind sacrificing.

Someone suggested ferric nitrate. That might work.

Remember, too, that acids will not affect the glass, so you can leave
them in contact for prolongued periods. Hence, you can use more
dilute acid and increase exposure time, making the whole process
safer.

Now, one further question: Are you sure that the mirror is silvered
and not "aluminized"? Modern mirrors typically have aluminum. 
Aluminum should be easier to remove, though, and I would have thought
that acid
would have done it. Lye will remove aluminum, but keep the exposure
time short because it will also slowly etch glass.

BTW, the clear glass (no green color) is likely due either to an
absence of iron (which makes glass green), indicating a pricey glass,
or to the presence of manganese (which imparts a magenta color which
"hides" the green).

Bruce
NJ

>>> "terry l. ridder" < terrylr at blauedonau.com > 7/18/2004 4:04:56 PM
>>>
hello;

well like edison i now know what does not work. ;-)

acetic acid does not work.
citric acid does not work.
phosphoric acid does not work.
hydrochloric acid does not work.

doing a further search on the internet it would appear that my options
are limited to sulfuric acid ( hot concentrated sulfuric acid ) or
dilute or concentrated nitric acid.

unless i am mistaken nitric acid is not something i can purchase at
stores like lowes, farm&fleet, etc. muratic acid ( hcl ) is ready
available which is why i tried it. sulfuric acid is battery acid but i
do not particularly care to work with hot concentrated sulfuric acid.

so would anyone have any suggestions where to obtain a half-gallon or
gallon of nitric acid. actually only need about a quart.

i did find that the red shop rags turn a dark blue when hcl acid is
poured on them. ;-)

On Sat, 17 Jul 2004, Andy Vida wrote:

"terry l. ridder" wrote:
terrylr> 
terrylr> hello;
terrylr> 
terrylr> now for the problem. the mirror is etched from the back. many
of the
terrylr> etchings are fine in detail there is no way for me to remove
the layers
terrylr> using a 3m stripper pad. so what would be a safe ( do not
want
to effect
terrylr> the glass in any manner, i.e. etch the glass or scratch the
glass) way
terrylr> to remove the protective layers from these fine details.
terrylr>

andy> 
andy> I know that nitric acid will etch away silver. As far as I
know
andy> it will not attack the glass. I believe it produce silver
nitrate,
andy> though not certain.
andy> 

terrylr>
terrylr> another note of interest is that when you look at the mirror
on edge
terrylr> there is no greenish tint to the glass, it is clear. i found
that
terrylr> interesting.
terrylr>

andy> 
andy> Typical of that sort of class. There is a nae for it, but I
andy> cannot dredge it up from memory just now. Soda glass, maybe?
andy> 

-- 
terry l. ridder ><>
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