hi! before you do anything
before you do anything else, i would suggest you get a level, at least a 12″ or 18″ long one, and use it to check and see if the kiln itself really is level, or just looks like it. i would check it along each of the edges and across the middle. if necessary, shim to achieve level. once i knew the kiln was level, i’d check the shelf inside, set on the usual kiln posts used to elevate from floor of kiln.
when you know the kiln and shelf are level, then i’d go to the bullseye site and in the education section there is a kiln test you can do to determine hot/cool spots inside the kiln when firing.
once you know what’s affecting the glass during the firing cycle, you can start trying to resolve any kiln problems. then it becomes a matter of using the right schedule and your slumping should be more consistently successful.
down in the valley……