For most bath salts recipes you can use your choice of Epsom salts or sea
salt, with baking soda, if desired, or a combination of all three. One good
mix is one cup of Epsom salts, with 1/4 cup of sea salt, and two or three
tablespoons of baking soda. A little more or less of each ingredient is fine
for most bath salts. Epsom salts and sea salt are soothing for tired
muscles, while both will gently soften the water for a luxurious bath
experience. You could also add a tablespoon or two of finely ground regular
oatmeal (not quick cooking) for silky, skin-softening water.

Fill each jar to the top with the combination of bath salts that you plan to
use. Add your choice of essential oil -
how many drops you use is a personal preference, but start with two or three
drops and see if you like the fragrance.
A good rule of thumb is to use 6 drops of essential oils per bath.
Stir the salts vigorously until all ingredients are thoroughly combined.