Good stuff for all of us
Good stuff indeed!
I keep thinking about how to create a perfectly definitive test and can't offer much improvement. For those that have seen MythBusters, there are always viewers critical of the methods used to debunk myths. If you have suggestions/improvements, please share before the glaze is applied.
For me, the emissivity difference between aluminum foil and glazed tile is something like 5% and near 90%. A used and charred cordierite pizza stone is near 90% - so we are good right? IMO, probably good enough. I might help if the stone was soiled again after the glaze firing to increase the emissivity from 70-something to 90%. (Assuming firing will likely clean the stone like new). That's my take, but improvements welcome. Otherwise, as long as the glaze side is non-porous and similarly smooth, I think we have a very good test.
Perhaps we refer to the fans of steam as Steamers, and the foil emissivity fans as Foiled Agains? Foiled Agains should enjoy knowing that the emissivity of paper up to 700F is comparable to stone, at 93% - helping support Craig's parchment paper observation.
(Here is the emissivity reference: http://www.omega.com/literature/transactions/volume1/emissivityb.html