Prepare the pure henna powder. Sift your supply of henna powder with a flour sifter or fine sieve. Measure ¼ cup of the sifted henna powder into a bowl.
Add the lemon or lime juice. This can be fresh juice, strained to remove the seeds and pulp, or bottled juice. If the bottled juice is concentrated, then reconstitute it to its normal strength with water first. Stir ½ cup of the lemon or lime juice into the henna powder. Combine well with a disposable stirring stick like a clean wooden popsicle stick or a wooden chopstick until the mixture becomes a thick uniform paste.
Add sugar or honey and essential oil. Stir in 2 tsp. of table sugar or honey and 2 tsp. of pure lavender or tea tree essential oil into the paste. Mix the paste until smooth.
Cover, set aside and let rest so that the dye matures. Use plastic wrap to tightly cover the surface of the mehndi mixture and set the bowl aside for one day in a dark and warm, but not hot, place.
Check the mehndi paste's consistency. Unwrap the mixture and stir. The paste should be neither too thin nor too thick. If the paste is too thick, add and stir in a very small amount of water at a time until it achieves the desired consistency.
Fill your applicator in preparation for using the mehndi. The applicator can be a small plastic applicator bottle with a plastic tip that has the desired width for your proposed design. Or you can use a plastic applicator cone -- this is very similar to a pastry chef's pastry cone. Otherwise, you can tightly cover the mehndi mixture until use and use fine mehndi or cosmetics applicator brushes to brush the henna paste onto the skin.