Wow Berlin - that's enough technical info to make my head spin.
I'll take it as "don't try the secondary air, go for the ceramic board".
I tried suspending a metal disk over the fire last night, but it doesn't seem to help much.
Web hits are pretty low when it comes to fiber board. Seems that soldering and kiln sites have some. Most sell in larger quantities, but a few below show smaller boards for sale.
Any idea which product would be most suitable at the following link? They have soft boards, hard boards, honeycomb board, etc.
also a link here too: http://www.progresstool.com/cat_soldering_board__block_all.cfm
Other sources anyone knows of?
Tempted to try a piece of ceramic tile, but it would probably just crack.