You might search via google for "electro less" plating. This is,
reportedly, a misnomer that referes to a non external electrical process.
Copper and nickel varieties, and I believe I've heard reference to gold
Typical approach is to metallize the plastic with a purely chemical
plating solution, then electroplate it with whatever the surface needs
Alternately, graphite is used to make the surface conductive enough to
Not all plastics can be plated. ABS is the best choice.
There are many companies that will metallize plastic objects on order,
and Caswell will provide the chemistry if one will do it oneself.
It's not so much of a misnomer. "Electro-less" plating has to do with
the molecular affinity of certain salts for surfaces which are of a
different dielectric charge. No current flows, only molecular and atomic
attractions are at work to cause the deposition of metals or salts on the
The most common way to plate plastics is to apply a very mildly-
conductive coating of a metal salt by means of an electro-less "seeding"
process. After that, first vanishingly small, then greater currents are
drawn in a plating solution to cause real metal to be deposited upon the
surface. Usually, that first plating is a more base metal like copper or
tin. After a suitable layer of the base is there, it is polished, and
then the precious metal is plated over that by normal means.
Someone with a little chemistry skills could "mirror" a surface with a
silver deposition solution similar to what is sometimes used to
(actually) "silver" mirrors. Then the silver can be used as the first
conductive base layer.
If you scrape nearly any metal-plated plastic item (like trim on cars),
you'll see a copper layer beneath the chromium.
You would need several layers to get finally to gold.
Perhaps start with something like stannous chloride,
then silver nitrate, then gold with electroless bath..
The coating propably includes nasty chemicals..
One kit that looks promising
but costs quite a lot.
I would get the parts coated at a local goldsmith.
I have done that a decade ago and the cost was very reasonable.
He used a cyanide bath that made the gold coating durable and non-porous.
A possible lead:
I worked with a guy who spend some time working in a fishing lure factory.
They would place bare plastic lure bodies in a cabinet. A partial vacuum
was drawn inside the cabinet (I don't know how much).
Inside the cabinet an aluminium slug was vaporized by passing a large
current pulse through it. He said the lures came out with a mirror
finish if aluminium on them.
That's also how they do telescope mirrors, but IIRC they draw a very
hard vaccum on the box. Some amateurs have set up their own rig, which
is an experiment in itself (everything has to be just so or you get
uneven coatings), but most just send it off to a vacuum plater for a fee.
It is called sputtering and was developed in the late 60's. TI was into
it in the mid 60's doing Ge and Si wafers for semiconductors.
Draw a good vac and then put an electric arc to the metal and it layers
over what is there.
A bit of black magic takes place but not to much. Spinning the disk helps.
On 3/10/2014 11:23 AM, Jon Danniken wrote:
That vacuum is *far* from partial. Any noticeable amount of air
left in there will slow the flow of molecules which you are trying to
coat things with. For a large enough bell jar to be useful, figure
perhaps 24 hours or more of roughing pumping with a good vacuum pump. A
bit less if you have a really expensive turbo-pump which you can fire up
when you get down to a low enough vacuum to speed the remaining pumping.
Otherwise, you get down to a certain level and then start alternately
chilling vac-sorb type pumps with liquid Nitrogen to adsorb what little
gas is left, and then valving them off and heating them to refresh the
core. Or an oil diffusion pump is a possible approach. All high vacuum
equipment is quite expensive.
Then you need a vacuum tight set of electrodes capable of 20 to
200 Amps, depending on the size of the "boat" (the part which holds the
aluminum or other metal to be evaporate. The boat is a folded piece of
something like nichrome clamped at the ends in the electrodes and spread
out in the middle to resemble a small boat, and filled with the material
to be evaporated. An alternative is a helix of wire (again like
Nichrome) with the ends clamped in the electrodes. A wire of the
material to be evaporated is wrapped around the helix of the wire, and
is evaporated when it reaches at least a red heat.
If the thickness of the coating is critical (it may be to reduce
your costs, given that you are using gold) you want a crystal oscillator
with the crystal surface exposed on one side, and to measure the
frequency shift to gauge the thickness deposited. And beware that a lot
more of your expensive material (gold) goes onto the inside of the bell
jar, and anywhere else inside (the clamps, and everything else).
The units which we used at work for making optical coatings onto
glass had a big Variac or Powerstat (at least 20A 240 VAC) controlling
the input to big transformers with really high current secondaries. (Big
enough so copper bus bar of about 3/8" thickness and 1-1/2" width was
used to conduct into the jar. And the "bell jar" was in reality a bit
stainless steel container with windows attached using Varian high vacuum
fittings with perhaps 12 or so stainless steel bolts holding them
together, with copper rings at the interface with a circular knife edge
from each side biting into it. And the copper rings had to be replaced
every time it was disassembled. (And it was disassembled and put into a
reflow "fume hood" where rather nasty acids were used to dissolve the
metals from the inside of the container.
So the requirement:
"but the base cost of kit, chemicals, materials needs to be kept
Is not that easy to meet. Chemicals don't apply until you start
cleaning the bell jar. The fume hood is an expensive installation,
especially since it has to be stainless steel to resist the acid fumes.
A big squirrel cage blower on the roof, and away from where anyone will
The "materials" would include the gold, including what was
But the "kit" (equipment) would be very expensive.
If you luck into all that hardware, you still need replacement
boats or helical wires, lots of power to feed into the pumps and so on.
Vacuum coat with copper (much less expensive) and then
electroplate with the gold, where you can control where it all goes.
Even ten to the minus 19 Torr is still a "partial vacuum". One freakin'
molecule per cubic meter is still a "partial vacuum". There's hardly any
such thing as a total vacuum, even in deep space.
Yeah, it's a _good_,_hard_ vacuum which might even be made better with a
cascade of mechanical and diffusion pumps, but don't mish-mash
terminology to fit your statements.
On Tuesday, March 11, 2014 6:44:18 AM UTC-4, Lloyd E. Sponenburgh wrote:
You are absolutely correct, but the term partial vacuum is a commonly used to mean the sort of vacuum you might use to vacuum bag epoxy resin, or degas resins. I do not say it is right, just that it is often used.
For vacuum depositing you need a vacuum where the mean free path is about as long as the diameter of the vacuum chamber.
yeah... I know. Just givin' you a hard time. Engineers have to "keep the
precision" (of measurements AND terminology)
Besides at 1x10minus19 Torr, that's only 0.1 atom per cubic meter. I guess
we could live with that! <G>
On 2014-03-11, Lloyd E. Sponenburgh <lloydspinsidemindspring.com> wrote:
Of course -- you can't get rid of the last few molecules, even
if you could stop the container from outgassing.
But when I hear "partial vacuum" thrown out casually (as it was
in the post to which I was following up) I read it as something between
what you can get with a shop-vac and a graphite vane pump. Not a
serious hard vacuum. Not enough to get a thermocouple vacuum gauge off
the "ATM" pin. :-)
A roughing pump, however, would get it fairly far down the
Any particular reason for swatting at me?
I was simply suggesting that the vacuum needed was not trivial
to accomplish with the contents of the average home shop. Yes, I have a
roughing pump in mine, but none of the other things needed to get a
No, Don. It wasn't directed specifically at you, except in the case that
you were the one who uttered the term.
I was 'swatting' at casual and careless use of terms that have specific
meaning. YOU may know what a 'partial vacuum' is, but many folks less
well versed may not.
If I were talking to someone, about the same subject, I'd _try_ to use
terms that actually described the vacuum. But I do it, too. I'd
probably just say "pull a good, hard vacuum below 10 microns Hg", or
something vague and imprecise like that.
A really well-maintained fridge pump with fresh oil will get down
_around_ where you need to be for vapor deposition processes, but not
easily, and usually not quite.
You need below 2u Hg to be effective, and most Robinaires won't get below
ten once they're a couple of years old. I mean, my Robinair thermistor
gauge won't read below 50!
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