5 ounces tartaric acid
6 drops lavender, rosemary, or rose geranium oil
3 ounces cornstarch
5 ounces bicarbonate of soda (baking soda)
Crush and mix tartaric acid, bicarbonate of soda, and cornstarch in a bowl. Place in a glass jar and add the oil. Close jar tightly and shake several times a day for 2 days to develop the fragrance.
To use, start hot water and drop about 1/2 cup into the tub as it fills.