Calculated stress distributions within materials sealed together across planar interfaces and having subsequently undergone differential dimensional change were compared with values measured in glass composite pairs sealed together at high temperature and slowly cooled. Where interdiffusion had occurred, dramatic departures from simple theory were observed both in the magnitude and in the sign of the corresponding stresses.

Chill checks of controlled depth were produced in soda-lime-silica glass, and an optimum humidity of 30 kPa (300 mbar) water vapor pressure was found to heal these checks in an annealing cycle. Critical factors were found to be afEuxing effect, having a direct dependence on moisture, followed by a drying operation at the annealing temperature. A four-step model is proposed for crack healing: (I) exposure of the crack surface to moisture at temperatures below TB, (2) formation of a gel layer, (3) closure of the crack resulting from the relief of stress (a minimum of 10 to 20 MPa applied compressive stress was determined to be necessary f o r complete closure), and ( 4 ) drying in the presence of a controlled atmosphere. [