RELATION OF ENAMELING IRON PREPARATION AND ACCESSORY CONDITIONS TO COPPERHEAD-TYPE DEFECTS*

The tendency of blue ground-coat enamels to copperhead is shown to be related to residual iron salts formed on the surfaces of enameling iron sheets in sulfuric acid pickling. Ferrous sulfate generated in the pickling oxidizes and hydrolyzes readily into compounds which are not soluble in cyanide neutralizer. These effects may be retarded by keeping the solutions between the sulfuric acid and the neutralizer slightly acid and by minimizing the time in these solutions and the exposure to air in transferring between them. The determination of these conditions and the establishment of satisfactory procedures in the production process are described. Some accessory conditions which affect copperheading are also included.