Color and appearance – most of essential oil show itself as light-yellow oil transparent liquid, and colorless, yellow-brown, red, blue, blue-green, and a few essential oil are solid (Yu Chuangmu)
Smell – with a special aroma
Volatility — volatilizable at normal temperature
Proportion – most of them are lighter than water, and a few are heavier than water.
Solubility – soluble in organic solvent
The refractive index – all has strong refraction,which will be higher when long or improper storage, and will change when there are impurities.
Oxidative polymerization – if laid up in air or sunshine for long time, it will gradually oxidize and deteriorate.