Old Linseed Oil
Linseed oil doesn’t dry very hard, no matter how long you wait, and that’s why it’s usually considered a bad idea to use too much of it directly on the wood before varnishing, since it could dampen the sound of the instrument. One day in 1995 I decided to pour some about 3mm deep in a pie pan, to see what would happen.
It took a year or so to dry all of the way through (for months there was a thick oil syrup on the bottom, next to the pan), but the crinkly shrinking started right away, as did the darkening of the color. When the oil underneath dries, This photo is of an area of the oil about the size of a business card. Now the oil is as stiff as an art gum eraser, but a bit stretchy, too. It hasn’t changed at all in the last decade or so.