As a part of nature, essential oils are both tools of a healing art and chemical components of a healing science. Essential oils are volatile substances contained within the plant that are released primarily through a distillation process. True aromatherapy uses only pure essential oils that are valued according to the extraction difficulty and according to the quantity of oil in the plant. On average, one ounce of plant material will yield about one drop of pure essential oil. More than one thousand pounds of Rose petals are required to produce just one pound of Rose essential oil.