Advice needed on use of Silver Nitrate on plastics
Andy Clews
I have long known about the use of Silver Nitrate for coating telescope
mirrors in metallic silver, but I have another application and I would like
some advice on this.
I enjoy scale model building, particularly models from the American space
program, all from plastic kits (so far). One of the kits I will be starting
soon is that of the Apollo Command Module. In real life, the CM had a
highly reflective mirror finish (before re-entry, that is) and I was looking
for ways of duplicating this. "Silver" paint just isn't shiny enough, and I
suddenly thought of the silver nitrate method.
Could anyone advise me on the efficacy of this? Would silver nitrate deposit
a silver coating on polystyrene as it does on glass? Would I be able to
protect such a coating from oxidisation, using varnish? Would polystyrene be
adversely affected by silver nitrate? (I'd be not a little p*ssed off if my
CM dissolved away before my eyes!)
How safe is silver nitrate to handle? Should I take any special precautions?
I do not normally read this newsgroup, but I'll scan it for the next week or
two for any followups to my questions. Otherwise please feel free to e-mail
me (an...@syma.sussex.ac.uk) if you can help. I'll be very grateful.
--
Andy Clews, Computing Service, Univ. of Sussex, Brighton BN1 9QN, England
JANET: an...@syma.sussex.ac.uk BITNET: andy%syma.sus...@uk.ac
Doug McDonald
>This is a bit of a naive question. I am not a chemist.
>
>I have long known about the use of Silver Nitrate for coating telescope
>mirrors in metallic silver, but I have another application and I would like
>some advice on this.
>
>I enjoy scale model building, particularly models from the American space
>program, all from plastic kits (so far). One of the kits I will be starting
>soon is that of the Apollo Command Module. In real life, the CM had a
>highly reflective mirror finish (before re-entry, that is) and I was looking
>for ways of duplicating this. "Silver" paint just isn't shiny enough, and I
>suddenly thought of the silver nitrate method.
>
>Could anyone advise me on the efficacy of this? Would silver nitrate deposit
>a silver coating on polystyrene as it does on glass?
tough to do with plastic.
>Would I be able to
>protect such a coating from oxidisation, using varnish?
Yes.
>Would polystyrene be
>adversely affected by silver nitrate? (I'd be not a little p*ssed off if my
>CM dissolved away before my eyes!)
Not if done right.
>
>How safe is silver nitrate to handle?
Silver nitrate itself is moderately obnoxious, quite poisonous, and
very prone to producing stains (remove them with Farmer's reducer
from the photo store.)
**HOWEVER** the silvering solutions are prone to violent explosions!!!!!!!
^^^^^^^^^^
>Should I take any special precautions?
Yes. Read the instructions in Amateur Telescope Making several times
very carefully. It is going to be VERY hard to get the stuff clean
enough.
I have done this with never an explosion. Our glass shop does it
routinely. Doing it right is an art.
Doug McDonald
Larry Lippman
> >I have long known about the use of Silver Nitrate for coating telescope
> >mirrors in metallic silver, but I have another application and I would like
> >some advice on this.
> >
> >I enjoy scale model building, particularly models from the American space
> >program, all from plastic kits (so far).
> >suddenly thought of the silver nitrate method.
The best way to coat your models is using aluminum through the
process of vacuum metallization. This is the same technique used to create
shiny metallic finishes on plastics, such as decorative bottle tops, knobs,
etc. It is a very inexpensive technique. Unfortunately, there is no way
to do this at home. I am surprised your model kit vendor does not use
this technique. Other metallization techniques, such as sputtering, may
not work as well due to possible overheating of the plastic specimen.
You might try your friendly university physics department to see if they
have any metallization apparatus.
> Yes, it will work **IF** you get the surface **CLEAN**. This is very
> tough to do with plastic.
Cleanliness is indeed a problem for chemical silvering techniques.
While it is rather easy to remove organic matter and other foreign material
from glass using nitric acid solutions, such an approach may not go over
as well with plastic. Nor is it particularly advisable for home use. :-)
> >Would polystyrene be adversely affected by silver nitrate?
>
> Not if done right.
Silver nitrate is reactive with some polymers, but I am not certain
which ones. Offhand, the only thing I recall is that silver nitrate will
cause a virtual explosive polymerization of acrylonitrile.
> >How safe is silver nitrate to handle?
> Silver nitrate itself is moderately obnoxious, quite poisonous, and
> very prone to producing stains (remove them with Farmer's reducer
> from the photo store.)
>
> **HOWEVER** the silvering solutions are prone to violent explosions!!!!!!!
Some silvering recipes are potentially explosive, and some are not.
A "traditional" silvering method uses Brashear's Silvering Solution,
which consists of an alkaline ammoniacal silver oxide combined with glucose.
Concentrated Brashear's solution which is left standing may form highly
explosive silver amide and trisilver nitride. Brashear's solution is usually
prepared just prior to use, with excess promptly diluted and safely disposed
of.
Another potential problem involves ammoniacal silver nitrate to
which sodium hydrpxide has been added (also used in silvering). Such a
solution may form a precipitate of explosive trisilver nitride.
There is a safer silvering method which uses silver nitrate, sodium
hydroxide, sulfuric acid, stannous chloride and dextrose. I don't recall
the recipe or exact procedure, however.
> I have done this with never an explosion. Our glass shop does it
> routinely. Doing it right is an art.
It sure is an "art", alright! I have never had satisfactory results
with in-house attempts at silvering. If we didn't botch the silvering,
we botched the protective coating. One simply cannot compete with someone
who does this work on a regular basis.
Larry Lippman @ Recognition Research Corp. "Have you hugged your cat today?"
VOICE: 716/688-1231 {boulder, rutgers, watmath}!ub!kitty!larry
FAX: 716/741-9635 {utzoo, uunet}!/ \aerion!larry
Jeff Forbes
> The best way to coat your models is using aluminum through the
>process of vacuum metallization. This is the same technique used to create
>shiny metallic finishes on plastics, such as decorative bottle tops, knobs,
>etc. It is a very inexpensive technique. Unfortunately, there is no way
>to do this at home.
Sure there is, a friend and I set up a vacuum evaporator in his basement.
You just have to know where the right dumpsters and junk yards are.
We were able to make aluminum mirrors on a number of things, but plastic
is much more difficult than glass, especially if it gets warm and starts to
out-gas.
Jeff Forbes
"....I have not failed. I've just found 10,000 ways that won't work."
Thomas Edison
Andy Clews
> The best way to coat your models is using aluminum through the
> I am surprised your model kit vendor does not use this technique.
The kit I'm primarily interested in treating is the 1/32 scale Apollo
Command Module from Monogram. The surface of the parts for the CM *are*
already coated but with a GOLD-like plating, which is wrong because the real
Apollo CM had a silvery (shiny aluminum or steel?) skin. My desire for
a silver coating is part of my quest for realism. I cannot understand why
Monogram didn't use a chrome plating on the plastic.
I would like to thank those who have so far posted followups to my question.
I must admit to being discouraged from the silver nitrate plating method,
not only because of the potential dangers but also because I've been
told locally that the minimum quantity of silver nitrate I could buy, would
cost more than the kit did... *sigh*
If I find a satisfactory solution (no pun intended) I will post it, just in
case someone out there is interested.