In the most commonly accepted “tempering” process, both surfaces of the hardboard are
flooded with a drying oil shortly after emerging from the hot-press. Linseed oil is most commonly
used. Excess oil is squeezed off and the board is then heat treated in a circulating hot-air
oven for several hours to cure the oil. The oil does not saturate the board. It only penetrates a
little way below the surface.
Tempering gives a harder, more paintable surface, greater strenth and more
resistance to liquid water.
AS I ALSO make pottery on a wheel, i have round MASONITE boards......we call em "bats." and these are subjected to a lot water when making pottery of the wheel. also whe you cut the clay from the "bat" the OIL in the board......makes the pottery piece slide smoothly and keeps the water out.