When painting eyes in a portrait, eyelashes are sometimes the final touch and can make or break your work. All eyelashes are not created equal. Sometimes just a few strokes of the brush is all that is needed to give the suggestion of lashes. Other times it is necessary to delicately detail lashes since that is the feature you want to stand out.
One of the things to remember when painting eyelashes is to study your model or reference photo. Seldom are human eyes lashes uniformly straight up from the eyelid. Even so this is a common way for beginning artists to paint them. If you look carefully, you will see that the top lashes usually go off to the side, then gently lift upward. The bottom lashes are similar.
Be careful when painting eyelashes on male subjects. Too much paint and they will look too dark. The same is true on children. A good technique to follow is to use a tiny brush, and to use quick strokes. Stand back and view the painting before adding more. Often times just a few strokes is all you need. Paint too many and you may be unhappy. It’s easy to overdo eyelashes.
When I paint portraits I like to paint the eyes, and then the eyelashes last. The reason is that the eyes define a person and finalize the portrait in a sense. There are other portions of the eye that need to be painted correctly of course as well. When it comes to the eyelashes however, sometimes less is more. My advise it to use a tiny detail brush, quick strokes and to know when to stop!