Constructing a Liquid Mirror using gallium,Indium, tin alloy

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jaxart
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Hi,
I am an an artist hoping that you scientists can kindly help me with some advice.
I am making a simple liquid mirror as part of a project about reflected image. It will spin and stop and spin and stop etc.
I have made a polyester resin parabola as a receptical (so that I can use less alloy) and am spinning it on a record player (for testing). I am using a gallium, indium, tin alloy as, in uk, it is by far cheaper than gallium indium or simply gallium.
It kind of works but not perfectly. Firstly, almost a thin scum seems to gather on the surface whereas I am looking for a real mirror finish. Is that the tin element or would it work like that even with pure gallium? Secondly, when I stop the spin, most of the alloy rolls back into the centre of the resin container. I had (perhaps niavely) expected it all to roll back rather than have a layer cling to the sides. I would be very grateful for any advice you can offer?
 
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From what little I know of liquid mirrors, the real 'art' (sorry..) is maintaining the rotation rate perfectly constant: any high frequency jitter will result in surface waves, destroying the optical figure.

In terms of the surface scum- it's most likely contamination- AFAIK, the solution is to regularly scrape off that layer (this was true for Hg mirrors). Material that 'clings' to the resin is probably wetting the resin- I don't know enough of the relevant chemistry to suggest a surface treatment, tho.
 
Well I also know very little about liquid mirrors, but what I found about Galinstan it is really sticky and adhere to almost anything. To prevent it the surface has to be treated with gallium oxide (maybe there other treatments, but i do not know).
About that scum - From what i have seen it resmbles colling tin so maybe higher temperature might help. But i do not know if it is safe to heat Galinstan so check it first.