Re: plating xmas balls

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: Jim Lux <jimlux-at-earthlink-dot-net> 

At 12:02 PM 12/10/2003 -0700, you wrote:
>Original poster: dave pierson <davep-at-quik-dot-com>
>
>>Xmas decorations now fill the shops. I have seen silver 8-inch diameter 
>>globes, which are probably aluminum coated plastic. Discharges strip the 
>>coating. Now if I could metal plate one it may make a nice topload for a 
>>small coil. I know its possible to plate almost any metal on any other 
>>but some processes require nasty chemicals. The only simple solution I 
>>could think of was ammoniacal copper. It will deposit copper and will not 
>>dissolve the aluminum. Anybody else got any suggestions involving readily 
>>available chemicals and anode material. Chrome would be nice.
>
>
>    What little I have read is that chrome is tricky to do.
>    Requires HIGH currents and many/most chrome compounds are
>    toxic/carcinogenic or both.  Yes, commercial shops do it...
>    In General chrome goes on over an undercoat of something else,
>    typically (ahemmm) copper.

Indeed, this is because copper is soft and easily polished, so that the 
thin, hard layer of chromium will wind up being shiny and smooth with no 
further work needed.

Nickel is also used as an intermediate coat.

Chrome, while nice and shiny, is probably not a good plating for a HV 
terminal (it's somewhat resistive, etc.)

Perhaps Gold (a thin layer doesn't cost much) might be good, takes a good 
polish, looks nice, is a reasonably good conductor, doesn't tarnish.

Silver has the nice property that the oxide is also a conductor, but it 
does tarnish.

Overall, unless you need that "silvery" look, copper is probably your best 
bet.. it takes a nice polish, is a good conductor, you can solder to it, 
and it doesn' tarnish or oxidize too quickly.

If you want a "real thin" layer, then you want to look into evaporating 
metal onto the surface.  There are a fair number of places that do this 
(how to make ANYTHING into a mirror...) and it's quite reasonably 
priced.  The problem is that the layer will be very thin (a few atoms), so, 
while it will look good, its electrical properties might not be what you'd 
hope.

Although, consider this... a thin layer of aluminum evaporated over a 
polished copper base that has been electroplated, then a layer of Aluminum 
Oxide over the aluminum to keep it shiny.  This probably wouldn't be all 
that expensive (in the overall scheme of things... it might be several 
hundred dollars, though).  You want to search for "vacuum metalizing" or 
words like that...
Here's a place in Rancho Cucamonga (a bit east of Los Angeles) that does 
metalizing:
http://www.vacmet-dot-com/

here's a company that electroplates plastic with copper/nickel/chrome 
http://www.customcoatings-dot-net/ccep.htm

There's also a process of sprayable metal finish: 
http://www.metalitek-dot-com/sprayable_metal.html

Says you can spray it on with conventional HVLP sprayers and it can be 
polished, etc.  10mil coatings...

And more traditional metal spraying (arc jet, etc.)
http://www.sculptor-dot-org/Foundries/MetalSpray.htm


Clearly, sitting down with the big green Thomas Register might be a useful 
strategy...