CHIPS, FISH SCALES, AND SHINERS, IV

The effusion of hydrogen from enameled steel to cause fractures in the enamel was investigated in an attempt to show that this gas may cause defects that range from plate-like fractures, or “chips,” through the known types of fish scales to the most minute shiner. The difference in the appearance of these defects was found to depend principally on differences in (1) the physical properties of the enamel, (2) the metal-enamel bond, and (3) the rate, quantity, and localization of the hydrogen effusion. Reboiling is shown to be related to fish scaling and to the other fracture-type defects because all are primarily hydrogen functions. The principal source of the critical quantities of hydrogen necessary to cause the defects is often found in the water of hydration in the dried slip, and the injection of hydrogen by that water during firing is demonstrated by experiment just as was shown for blister-type defects (see this issue, pp. 180-90). The prevention of fracture-type defects is discussed, and some novel effects of protective surface oxidation are illustrated.