Okay – here are a couple
Okay – here are a couple thoughts. I’m not convinced any of them are correct – but it is the best I can come up with for possible reasons on getting devit in part of a kiln and not the rest.
– Are all the elements working? Maybe having some elements out is causing significantly uneven heating in the kiln?
– Is anything going on on the inside of the lid (perhaps an element sagging into the groove) that is causing kiln brick dust to fall onto some of the work? Brick dust can provide the “seed” for devit to grow.
– Is there anything about how the kiln shelf is supported that would cause one side of the shelf to cool much more quickly than the other side?
The only other thing I can think of is there is some subtle habit you have about loading the kiln that is the culprit. Maybe you always load in the order of the spectrum (remember ROY G BIV?) which would put all the red pieces to the left. Reds tend to devit more easily than most other colors.
These are all kind of wacky theories – but you have a wacky issue 
Have you done a controlled test to confirm the problem is what it appears to be? For example, place 1/2″ square tiles across the whole shelf and fire to full fuse? I’d use red opaque glass to maximize the results.
Paul
Paul
FusedGlass.Org
Helios Kiln Glass Studio
PaulTarlow.com
