I totally get it and would probably do the same for something I needed to rely on.
Kaolin is like 40% aluminum and has silicon in it. Which I am guessing forms silicate alumina when it is baked.
This is kind of for my own notes which I am sharing. I apologize
"I use a fumed silica solution (water and fumed silica) for rigidizer. I’ll combine this rigidizer with zircopax and kaolin (range of 3:1 or 4:1 ratio of zircopax to kaolin) to make a very economical reflective coating. It will eventually wear out over use, but it’s reasonably tough and does a nice job making the forge reflect heat. I also paint this on the hard fire brick that I use to block the front opening of the forge - I paid for that heat, and I don’t want it to escape without doing some work. ITC 100 is nifty stuff, but I like the price of my home brew coating better." Then someone else mentioned itc100 was designed to wear out also…