21″ Round X 3/4″ (533 mm x 19 mm) half kiln shelf. Half shelves are easier to load because they are lighter and smaller than full shelves. Half shelves also allow you to stagger the height of each layer in ceramic firings. Line up two half shelves so that one is about 2″ (50 mm) higher than the other. This improves air circulation in the kiln. Protect your shelves with kiln wash (or glass separator, if you fuse glass). Paragon’s cordierite shelves are volume-stable.