I was loading the kiln for glaze, and I found a number of cones that don’t have an unglazed bottom. These can’t be fired because they will stick to the shelf. I’m not sure who made these, but there are several glazed this way.
My recommendation is to wet a sponge and wash off one surface so that the cones can lay on the shelf without sticking to it. We have some stilts, but not enough for this. Plus, all of our stilts have been used, so there’s no guarantee that they won’t collapse on this use. If you decide to use stilts, make sure you get ones that are graded for Cone 6 firing. Any of the stilts will probably be okay for one or two uses. If you own the stilts, you can keep track of how many times they’ve been used.