Peel the potatoes and cut them in the (relative) shapes you want, typically squares or rectangles. (They dry how ever "they" want, it is not completely controllable). Put toothpicks, wire or something inside them to keep a hole in them. Let them dry about a week.
You can speed up the process a bit by microwaving them a couple of minutes (don't microwave wired ones, of course). Then paint (or not, they tend to become very black), varnish in some manner, string. Mine developed some mold, so I am thinking next time of dipping them in apple cider vinegar (which kills germs and mold) first. Other posts I have read on the subject haven't mentioned mold, maybe it wasn't an issue for them.
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