[ATM] Removing a chrome(?) coating layer

[Guntram Lampert <glampert@aon.at>]

Hi all,

A few days ago, I tried to remove a mirror coating by polishing it off 
since I intended to do some figuring anyway.

A first layer came off pretty quickly, followed by a second one that 
left a dark grey residue on the lap. No doubt this was the aluminium. 
But now I am left with a metallic layer that I suspect is chromium. I 
once read that it is used as a first layer to improve the adherence of 
the aluminium.

Now, I can´t get rid of this first layer. Treating it with diluted 
hydrochloric acid, no result. Added ferrous chloride solution, nothing.

Rubbed it with "soft" abrasives, remains there.

What to do?

Thanks for suggestions,

Guntram Lampert
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