Huw
Not ignoring you mate.
I don't know enough about staining and the removal process with the farrow System to be able to tell you absolutely it is the answer.
Chris may know he seems to have more experience with blasting. If he says it is doable I am happy to come over and get some fine olivine ordered and go from there.
Rob
Poltice
It looks like the stain is "in" the structure as opposed to "on ".
Robs machine is really designed for "removing" stuff from the surface ( although not grease!) and care will always be needed to not "remove" the substrate .
Try
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