Grace Wilson, IntentBlog 

This is a simple process, if you're willing to give it some time and
attention. The idea is to boil your herbs in water first, infusing the water with the herbs and their healing properties. When you strain the leftover herbs from the water after boiling, you have a decoction (as in an herbal tea).

Then, to get the infusion of herbs into the oil, you add the decoction to the oil, and boil until all the water evaporates.

Ingredients:
-½ cup dried herbs
-4 cups water
-2 cups oil

To make the decoction, boil ½ cup of dried herbs in 2 cups of water. (Dried herbs are traditionally used because their properties are more easily assimilated into other media, such as oil or water.) Boil over a low flame until the liquid is reduced down to 2 cups of water. Then strain the liquid with a fine strainer.

To herbalize the oil with the decoction, combine equal parts of
decoction and oil (e.g. 2 cups decoction and 2 cups oil). Boil over a low flame until all the water evaporates. You can test the oil to see if all the water is gone by adding a drop of water to the boiling mixture.

If the drop of water crackles or pops, all the water is gone, and your herbalized oil is ready. Cool before use. Result = 2 cups of herbalized oil.