A block in need of cleaning.
This block comes from a recorder that had been regularly used for several years but then started to play badly. The tone became coarse and the top notes difficult. Note the build up of a white substance which has rounded the chamfer and rough areas along the length of the windway floor. (White foreign matter is unusual, I don't know what it is.)
After careful cleaning the block appearance and the playing characteristics of the recorder were as good as new. I prefer to use a very sharp blade to scrape away foreign matter. The angles must on no account be rounded or altered. It is my opinion that any sort of abrasive paper, even when supported, is a very bad idea. Some foreign matter, usually black, will wash off. One has to be very quick otherwise the wood may swell and the block becomes difficult to re-fit. Any fine finishing with a scraper must only be done when the wood is completely dry.