Glenn Herbert wrote:Not getting into the toxicity or lack thereof, I have a few questions and comments about your math and chemistry. First, did the manufacturer say the 25% is by volume or by weight, and is that aluminum or aluminum oxide? Those factors would significantly affect the amount of aluminum in the bricks. I think the relevant factor is how big a volume weighs a milligram, thus how much powder would need to be scraped off with each pizza to be hazardous. If a milligram of firebrick powder (1/4 aluminum or 1/4 aluminum oxide, whichever it is) is a decent pinch, I think we can agree that nowhere near that much comes off with each pizza, let alone gets into the food or air that a person consumes. Hard firebrick are quite abrasion resistant, soft firebrick are not (and thus are not suitable in any way for an oven floor). I don't have equipment to measure a milligram of firebrick powder, but I could weigh out 0.1 gram and see how big a pile/pinch it is.