Q: Beth, ...I do not have anything to stack and fire plates at all, so I am
wondering if I need to get something to stack them when glaze firing. I read that
firing them standing up in the bisque fire helps reduce warping, but you can't do
this in glaze firing. What is the best way to glaze fire plates?
A: This was actually my first time to try out pronged plate sitters (a type of kiln furniture that helps you get a tighter stack without having to use umpteen kiln shelves). Usually, I fire my plates flat on the shelves, with two inch posts between shelf layers --- so it does use a lot of kiln shelves. However, I have not had any plates sag or warp on me this way for a very, very long time!
Bisque firing plates (or tiles) on their side is not something I really recommend. Yes, it saves kiln space as you stack, but it can actually cause warpage sometimes. Any time the clay is not supported fully (e.g. the floor and the almost-horizontal walls of the plate) there is the potential for the clay to sag (warp).
As far as glaze firing, plates (and tiles) should be kept horizontal if there is any chance of glaze dripping off. I will continue testing the plate sitters to determine the cause of my plates warping this last time. (Other plates in the same area of the kiln did not warp.) I know a lot of potters do use them or other specialized kiln furniture and get very good results.