Kilns fire a lot hotter than 400 degrees. They essentially melt glass, but if you find someone willing, that knows what they are doing they could adjust it to work for you, heating time and cooling time will be a little long and the size may be only large enough for one at a time depending. Give it a try though. (Now pottery is something I know about) Those things get really hot, so make sure whoever is operating the kilm knows what they are doing. hey may make you buy some 400 degree cones to get the temp right, but those aren't too expensive, but make sure they know what they are doing, or it may get a lot hotter real quick and damage your headers. it will take a few hours to heat up and a few more to cool down (thoe things are designed to heat up to over 2300 degrees F