An aluminium front surface mirror will be clouded and/or etched by quite weak solutions of either acid or alkali. Most developers and stop baths would do the trick. If the gelatin is porous enough to develop the emulsion fully the Al is likely to be corroded. You might be able to do something with a barrier layer of hardened gelatin.

Al ion in solution also interfere with the balance of Ag redox reactions. Most darkroom books advise against using Al trays for this reason. I'm not enough of a darkroom chemist to say how bad the effects are, but the warning makes sense to me.

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