[Pikko Nitro]

Hi everyone at Chemical Forum!

I make plastic parts, often covered in vacuum metalization process. Typically the vaporized metal is aluminum covered with transparent varnish and it produces well known chrome effect. I would like to achieve similar chrome finish but with colorful iridescent effect, like on bismuth crystals. As I know that iridescence is produced by hi refraction index difference between outside and inside layers and air. In case of bismuth it's made by bismuth oxides covering the metal.

I wonder if vacuum metalized bismuth layer cover with desired oxides. The process I'm mentioning is low temperature one and I'm not sure what was the lowest possible temperature to produce that oxides, I don't know what exactly oxide is responsible for this. The bismuth pellets I can buy are gray and unappealing, I guess they are uncovered or covered with wrong oxide.

Any help in that field will be appreciated

[Arkcon]

The entire reason for the rainbow birefringence of bismuth crystals is uneven oxide layers as the oxidation occurs on growing crystals.  If you get get that in a film, that would be very impressive, but I can't see how you're going to do it.  We've explained this once or twice  before: http://www.chemicalforums.com/index.php?topic=68084.msg245390#msg245390

[Pikko Nitro]

I'm going to vapor film of metallic bismuth under vacuum on plastic part. I don't know how to make that oxides film on it after taking out from vacuum chamber. Is it possible? I could for example use blowtorch to heat metal coating without melting underneath plastic. What do you think about it?

[billnotgatez]

... I could for example use blowtorch to heat metal coating without melting underneath plastic. ...

Based on forum rules we try to teach you how to find answers for yourself.
What do you think the melting points of the plastic and metal would have on your results?

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[Enthalpy]

A bad vacuum would be a great way to oxidize any metal during the deposition process - even metals resisting odixation. One thing that can go wrong is if the layer makes grains or doesn't adhere to the substrate. Also, the evaporated metal will scavenge much gas from the chamber when it evaporates (some vacuum pumps work by evaporating titanium) so it may need to introduce air permanently.