Today I became the proud owner of this old Stanley 71 router plane.
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I've always wanted one of these old planes so I picked one up in a trade. Anyway, when I got the plane it had some rust on the bottom seen in the picture below.
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I decided to try to remove the rust with a granite plate and some 220 adhesive backed sandpaper. After a couple of minutes of lightly working on the plane, most of the rust is gone, but now there is sort of a weird purple tint in a couple of places (directly below the handles).
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What is this purple tint? I have used this method on a couple of old stanley baileys, and I don't recall seeing any discoloration like this before.