Any good soap can be used to make bubble bath, but castille generally is
preferred. Before the soap can be made into bubble bath it must be
converted to a liquid. To do this, grate 1 bar of castille soap into 1
quart of water, warm water helps dissolve the soap faster. Allow the soap
and water to mix well so that you have a liquid soap solution. There are
two ingredients that can convert liquid soap into bubble bath. These
ingredients can be used together or independently of each other. An
old-fashion way to make bubble bath is to add Glycerine to liquid soap (
soap shaving and water.) Glycerine has the ability to make bubbles and
increase suds. Coconut oil is often used as a substitute for Glycerine,
which is usually much higher priced. Coconut oil is very effective at
creating lather. Both Glycerine and coconut oil are known for their
special skin-softening properties. Source:Making Potpourri Colonges and
Soaps;102 Natural Recipes