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Optical finish for polished aluminium

Does anybody know what is the highest level of reflectivity possible from chemical or mechanical polishing of aluminium?

I've been reading about the complexities of producing glass telescope mirrors and then coating them with aluminium to achieve >95% reflectivity. Forgive my ignorance, but I don't know why polished aluminium isn't used instead. (Am considering starting amateur telescope making as a hobby.)

Albert Deme
- Melbourne, Australia

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Similar to question #5080, I am also inquiring about reflectivity of polished aluminum. What is the best aluminum material to use? What is the best polishing process to use? How well does polished aluminum retain its finish, how long does it take to oxidize(Environmentally dependent?), does oxidation have a huge impact on reflectivity, can the oxide surface be polished? What protective finishes can be applied to the polished surface to prevent reflective degradation? (And possibly protect for general handling and cleaning).

The application requires mirror surfaces to reflect the infrared energy emitted from a heat source. Element temperature up to 1700 C. Reflectors will be water cooled, rectangular in form, and a variety of lengths.

MARK JENKINS
Design and manufacture: Bespoke automation machinery - Cambridge, England

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