A reputable manufacturer will carry out tests to to certify the authenticity of the essential oil. There are 3 tests:

• Chemical analysis
• Odour evaluation profile
• Specific gravity testing

Chemical analysis - Gas chromatography - the only sure method of measuring qualitive and quantitive composition of an essential oil. Expensive to carry out. Often the larger oil companies carryout spot tests of their oils using this method. Many smaller companies cannot provide this information on their oils. Click here for more information on gas chromatography

Odour evaluation profile - Experience of smelling different oils can be built up over time. Perfumiers can be in business for 15 - 20 years before they are considered to have refined their sense of smell enough to be able to detect if an oil has been adulterated. For the aromatherapist, this can be used to detect stale oils only. Thisis not a reliable method

Specific gravity testing - The density of an essential oil varies depending on its chemical make-up. Specific gravity is a measure of density of the oil as compared to the density of water, which is normally taken to be 1.0. Variations in specific gravity may indicate impurities being present in the oil.