And yes, that is a dark green stain with a marbled green band attached to a faux-amber stem.
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When I first found these stems I was all excited because I thought they were really beautiful, but when I went to sand and compound them, I quickly found they had a really strange characteristic - The exterior orange tint comes off! In the pic above, what you're seeing is the orange exterior coloring of the stem and the stem's face around the tenon is the pale white interior color, which becomes apparent the minute you do any sanding or firm compounding of the material, because the orange comes off like stain. It's very strange, and I've never encountered anything like it before. I don't know where the stems come from or how old they are, but the odds are, "very", so it's left me wondering if the color is an effect of oxidation on the stem exteriors over the years. Maybe they started off whitish and just yellowed on the surface with time. Because I can't imagine any manufacturer actually staining stems, and as it's some form of polyester resin cast, it would never penetrate anyway so its usefulness would be nil.
Weird.
My pipe's stem retains its color because all I did to it was flatten the end, drill the hole for the tenon and filter, and then *very* lightly clean buff the exterior, to avoid removing any of the color. This is fine for me but wouldn't be suitable for a pipe to sell, as it's got a number of fine scratches and surface ripples in it. Smokes great, and the color doesn't come off on my lips or in use, which makes me think oxidation of surface material is the answer.