Oxides and washes are mixtures of ceramic colorants (which are metal oxides) and water. They are very thin and watery since they contain little to no clay, fluxes, or other minerals.
A CAW standard is Red Iron Oxide, which consists of Iron Oxide mixed with water. This mixture is strong enough to darken an unglazed stoneware surface during firing. Sometimes oxides are used to sign a pot after bisque, in lieu of etching the greenware.