Raku is when pots are taken from the kiln while they are still glowing red hot, they are then placed in a material that would be able to easily catch fire, such as sawdust or newspaper. The reason for this is to starve the pot of oxygen, which gives the glaze a wonderful variety of colors. Pieces with no glaze on them take the oxygen from the clay itself, meaning some areas will have a matte black coloring. Raku differs to normal firing where the piece is removed from kiln after it’s cooled down slowly.
If you would like to put liquid in them you need to use a liner. A cut to size plastic bottom will work well. To clean the piece please use a damp cloth and wipe them down.