Lay pieces of white oak bark in a warm, dry area. Areas of natural sunlight and heat, such as window sills, are preferable. Allow the bark to dry until the inner side is dry to the touch and the bark becomes brittle.
Break the dry white oak bark into small chunks. Break the bark with your hands into pieces smaller than your palm.
Place the smaller chunks into a metal or wooden bowl and crush with a mallet. Pound gently until the bark becomes a powder. Stir the substance to ensure that all pieces of the bark are crushed.
Store in a clean, dry container.