They are available in glass and several kinds of plastic. Most people use 20 to 25 mL of medium in each petri dish. They are all called culture dishes. Most platic dishes are make of polystyrene and can't be autoclaved because they deform in the heat. Some plastic dishes can be autoclaved, but they are more expensive.
Most people autoclave glass dishes and medium separately.
When the medium is cooled to about 55 o C, they lift the lid of the dish enough to pour the the medium to the desired depth and lower the lid in place. If your dishes are autoclaveable, you may dispense the agar into the dish and then autoclave. A Useful Rule Don't waste too much time wishing for equipment you don't have. Spend your time thinking about things you can do with what you have or how to make a substitute. Huff St., Palmyra IN 47164 Please help by sending me an e-message containing your ideas for improvement.