A commercial machinable glass-ceramic (CGW-9658) had been found to change color, from white to dark-grey, upon exposure to H isotopes at 500C and above. This process was studied here, using optical microscopy and electron spin resonance, as a function of temperature, gas pressure and H isotope. The results revealed a one-to-one correspondence between the diffusion-controlled reduction of ferric iron by H and the visually observed width of the reacted zone. It was deduced that the activation energy for H permeation was 11.9kcal/mol.

Hydrogen Transport in a Machinable Glass-Ceramic. J.E.Shelby, J.Vitko: Journal of Non-Crystalline Solids, 1981, 45[1], 83-92