Your reading because your mixing henna and you want to learn more, or your wearing henna and you want to know why they are in there. Oils added to henna serve 2 purposes: they terp the henna (help break down the cell wall and release dye) or they are added to dilute the smell of the terping oils (short for oils with high monoterpene alcohols ) . Terping oils that are traditionally used do not smell the prettiest. I happen to like the smell of tea tree and eucalyptus, but you have to admit that wearing those oils can make you smell like you are medicating a condition. Still, they have the highest value for making your henna dark, and so many of us use them. Striking a balance between smelling really good and making henna dark is my mixing purpose, because even if you are only wearing the henna for 2-4 hours, you are less likely to remove the henna too early and use water to wash it off if you dont hate how it smells. I guess I just dont know too many people willing to plan their day around those 4 hours and beyond. You got groceries to buy....I get it! My favorite terping oil is Cajaput. It has the highest amount of terping alcohols, third in line to eucalyptus and tea tree. It is related to tea tree and so it smells a bit like it, but it is slightly less pungent and the ability to cover it is ever so slightly easier. I refuse to use eucalyptus because wearing large amounts of it can make the wearer feel ill. Same with tea tree, to a lesser extent. My second fave is Lavender oil, but not just any lavender oil will terp your henna. Lavender isnt super high in monoterpene alcohols, but high enough where it has value. Turns out, where its grown and what variety you use will determine if it does anything for your henna. Be picky. Use Lavender Angustifolia , ideally Bulgarian lavender.
If you are not convinced that one lavender is better than another, then you can go to New Directions Aromatics which links you, or any other oil supplier, and request a gas chromatography read. It is a break-down of the constituents that make up that crop....and you can see the percentage of terps in the result if you research . These are the two best oils to use as a foundation for your henna mixes. Other oils I use are Geranium or Rose Geranium (much more expensive) Frankincense , Clove, Sweet Orange, Vanilla (VERY expensive!) Patchouli, Vetiver, and Cardamom. Not all of these oils terp, and you never want to exceed 30mls of oil total per 100gms of powdered henna!
I personally do NOT add 30 mls, I use closer to 20-25mls because I use oils that are fresh and terp well. More is not better....and more can actually hurt the mix ( make the henna lines feather and run) and hurt your wallet! My advice is to begin getting used to using a mix of Cajaput and Lavender oils in varying ratios to see which you like best....then slowly work in other scents AFTER you have researched their terping value and safety on the skin. I recommend visiting The henna page for more detail - http://www.hennapage.com/henna/how/terp.html There is significantly more to say on this topic, but this is a great step for all who message me asking about mixing the first batch. Mixing henna is not hard, but like baking a cake you can screw up a nice batch of henna by being careless, cheap, and not paying attention to how long its cooking.