This section is from the book "The Boy Mechanic Vol. 2 1000 Things for Boys to Do", by Popular Mechanics Co.. Also available from Amazon: The Boy Mechanic, Vol2: 1000 Things for Boys to Do.
A broken oilstone can be repaired and made as good as new in the following manner: Warm the pieces by heating them on the top of a stove or gas heater, with a piece of heavy sheet metal placed on it so as to protect the stone from the direct heat of the flame. The heating should be done somewhat slowly or the stone will crack.
When the stone is warm wipe off the oil which the heat has driven out and apply a couple of coats of shellac to the broken ends. When the shellac is thoroughly dry, warm the stone again to melt the shellac, and clamp the pieces together. After cooling, the pieces will be found firmly stuck together. - Contributed by F. L. Sylvester, Reading, Mass.