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Aluminium is a fairly good reflector, but oxidation will reduce it's optical reflective properties.

Aluminium is used for reflectors either being deposited on a substrate, or polished and protected by a protective layer to avoid oxidation.

How will the oxide layer of a several year exposed polished aluminium (indoor) will impact the reflectivity.

Will it be considerable or minimal ?

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    $\begingroup$ Likely drastic. Telescope mirrors are made with a protective layer of SiO2. $\endgroup$
    – Karl
    Sep 11, 2018 at 5:45
  • $\begingroup$ @DrMoishePippik I haven't been able to find any sort of data of reflectivity of anodized aluminium unfortunately $\endgroup$
    – Damien
    Sep 12, 2018 at 4:41

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The lifetime of aluminum depends on the environment. If it's near an ocean, where air is humid and often contains salt particles, it may become pitted or look a milk white, rather than shiny, in just months. Anodizing can protect it for years, though.

Because the surface of anodized aluminum is porous (until sealed), it may have a somewhat more or less matte finish depending on treatment. Bright dip anodizing, depending on the aluminum alloy, offers a more shiny finish.

The Alzak process is used for lighting reflectors, and there is information on its specular reflectivity.

Alzak anodized mirror, http://www.miramarmetalprocessing.com/bright-dip-anodizing/alzak-reflector/

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