Each spring, oil colour makers Gamblin scrape the crap (err, very high quality pigment dust) off their air filters and turn it into “Gamblin Torrit Grey”. The colour is different every year due to the varying proportions of the pigments they handle. They then give away this paint and hold a competition wherein you enter something painted with only Torrit grey (plus any black or white oil paint).
(Painting via lizzconley - I saw this in my Flickr contacts stream and read about the backstory.)
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