Can't speak to red brick, pottery or pottery shelves, but I do know that firebrick, even at lower smoking heats carries & retains MUCH more heat than it's surrounding environment.....
Below are 'Turds that were sitting over the firebrick prop-up ~~~>
Anything touching, or very near the brick, will pick up, as a guess, maybe 75~100% again of the surrounding temprature.....puts a lower smoke @ 500 degrees......I believe hot enough to kill anything bogus.........
Pizza stones are usually run real high also, my own personal speculation would go along with 'hot enough' on those also........
Now, these are speculations & not scientifically proven stuff......so I'm gonna go lookin'.......