Clay for students includes firing fees. If you wish to wish to change your first bag of class which is included with your class, please choose the upgrade option. The upgrade option is only to change your first bag of clay included in your class fees. For any subsequent purchases, please choose the clay itself.Note that the 540i is a larger bag of clay than the others. M340 - buff - 22lb bagM340S -speckled buff - 22lb bagM370 - white - 22lb bagM390 - reddish brown - 22lb bagWheat - smooth buff - 22lb bag540i - black (dark grey) - 25lb bagReclaim - pugged mixture of all clays - 15lb bag