For a patch test, you only need a small fraction of the henna powder from one capsule. Open a capsule gently, and pour out less than half a pea sized amount onto a small dish. Mix this small quantity with two drops of water to conduct your patch test. There's no need to prepare the full mixture at this stage because the henna can lose efficacy over time if left sitting. The remaining henna powder inside the capsule can be safely stored for your actual brow application once your patch test is successfully completed and shows no signs of irritation after 24 hours. This way, you can ensure that the henna mix you use for your brows is as potent as possible.