Seriously, I was asked this. I find the question about like being asked how to make a violin -- I can tell you how to do it, but I make no promises about how well it will play.
Basically, you clean out the horn, block up the end with a wooden plug with a very tiny wind hole cut in one edge of it. This plug must be absolutely tight, and works best if you boil the end of the horn until it softens, and then insert the plug. Where the wind hole clears the seated plug inside the horn, carve a 45 degree angle slope, about a cm wide. The first holes should be drilled starting up about an inch (24mm) and then drill small (3-4 mm) holes in about 18 mm further on. From here you hand-carve the holes to tune the horn correctly. I've seen the suggestion that you drill an extra hole in the "back", to finger like a modern recorder -- I don't know anything about that.
Note that a properly made gemshorn will be very sensitive to humidity, and can lose tonal quality (temporarily) simply by playing it -- although this will be corrected as the horn dries back out. Others suggest keeping the horn wet all the time, although this means it will lose tonal quality as it dries out as you play it.
According to the OED, the term "gemshorn" doesn't show up in print in
English until 1825 or so, but there are 15th century illustrations of them.
What were they called before?
Using and working with Horn - Making a Gemshorn. Copyright ©
2001 I. Marc Carlson
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