Harvest your arnica flowers.
Allow them to dry out in the sun or a warm, dry place for about 30-60 minutes.
Fill a clean mason jar (any size) with arnica flowers.
Cover the flowers with oil.
Secure with a lid and place in a cool, dark place for 4 weeks.
Shaking the jar several times a day for the first week, and then once daily for the remainder of the four weeks.
Strain flowers out using a fine mesh sieve or butter-muslin and store oil in a sealed jar in a cool area, out of direct sunlight.