About your Raku Ceramic
Your ceramic was made from a special clay designed to withstand tremendous thermal shock. The ceramic was constructed from wet clay, dried, and then fired in an electric bisque kiln to set the clay body and remove the chemical water from the clay body. The ceramic was then glazed with glazes designed for the Raku firing process. The glazed ceramic was then fired in a outdoor gas fired kiln to a temperature of 1850 degrees. While the ceramic was still at high temperature it was removed from the kiln and placed in a container full of combustible materials (paper, sawdust, etc), the container was allowed to catch fire and quickly covered to extinguish the flames and seal the container. This allows the ceramic to cool in a oxygen free (reducing) atmosphere. This causes the Raku glazes to reduce and produce a wide range of colors only obtainable in a reducing atmosphere.
When the ceramic has cooled sufficiently to allow it to be removed from the reduction container it is then either allowed to finish cooling in the air or is quickly cooled in a water bath. This ensures the glazes will be completely color set.
The ceramic is the cleaned with a stiff brush and soapy water to remove any surface soot and carbon. Any part of the ceramic that did not have any glaze will have absorbed carbon from the combustion chamber and it will be chemically bonded to the clay body (and will be permanently black). When the pot has dried after cleaning, I apply a protective coating of synthetic “wax”. The “wax” is an acrylic which polymerizes on drying to provide a thin protective non yellowing coating. The acrylic is resistant to water or acidic solutions but can be removed by washing the ceramic in a high pH solution like a strong soap, ammonia, or soda (baking soda in water).
I recommend that you use your ceramic for decorative (art) uses but it can be used for dry storage and where applicable for storage of kitchen utensils, knitting needles, etc. These ceramics are not suitable for use as water filled vases without the use of a glass insert. These are relatively low temperature fired ceramics and the clay body has not vitrified so water will eventually move through the clay body if it is stored in the vessel (the clay body is still porous).
I do not recommend the use of these ceramics for food uses as the glazes on many of them contain metals such as tin, copper, zinc, iron, and silver. The acrylic will provide some level of protection for dry food stuffs.
For cleaning, I recommend washing in a water bath and or with vinegar as this will preserve the acrylic coating on the ceramic. Allow the ceramic to air dry, They should not be washed in a dish washer as this will remove the acrylic coating.