Could that brick have been stacked on edge with another brick stacked
against it in the middle? Vitrification can partially extend into covered
areas. I'd like to see the brick.
Anyway. I'm sure 'sacrificial' bricks were sometimes used for lining fire
channels to protect the other bricks but I do know for certain that it was
common practise to place underfired bricks into the next burning. A
careless apprentice may have stacked a vitrified brick in by accident for
refiring.
Cheers, Robert
Archaeologist & Heritage Consultant
ph: + 61 + 2 43882169 fax: + 61 + 2 43898450
http://www.geocities.com/Paris/LeftBank/6559
31 Wombat St Berkeleyvale NSW Australia 2261