of the sheet or foil a fully hardened sheet or foil i e one having a cold rolled temper may therefore be obtained by this form of heating or drying the heating or drying time may be the minimum required to achieve full evaporation of the solution which may be several hours if the foil is in coil form longer heating times are not required but would not be harmful as the structure of the metal is not changed by the applied temperature as an example the sheet or foil may be kept at 100 u00b0 c for 4 to 5 hours which is just adequate to evaporate all of the isopropanol when this material is used as the polar solvent and the foil is treated in the form of a coil having a weight of 2000 pounds alternatively in a second form of the heating or drying procedure which may be referred to as a high temperature treatment the heating may be carried out at a temperature of 240 u00b0 c or above at this temperature not only is the polar solvent evaporated fully but the metal may be partially or fully annealed if a u201c fully hard u201d foil is still required the heating time should be maintained for just long enough to remove the polar solvent but not long enough.