Different bits of wood! In the thumbnail you see an MDF one, but I use plywood or all sorts of things. Usually scraps I find for free. The work surface I use is called a wedging board, you can find a tutorial for that on my other channel here: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-J6oh3QEu6KY.html
I'm wondering what I don't know. It looks like you are placing glazed pieces directly onto the kiln shelf without either stilting or wiping the glaze off the edges and bottom. What am I missing?