Hi William! It depends on which harmonic you’re playing. If you are playing the natural harmonic located just beyond 3rd position, straighten out the pinkie and play it with the pad of your finger. There are additional natural harmonics located just under the fingertips, too. An example: Each 1st position, 3rd finger – on D, A and E string. You should use the fingertip to play these. You can also produce ‘fingered’ harmonics anywhere on the violin by playing the 1st finger normally, then using the 4th finger as the harmonic. I found a good video that explains harmonics on the violin and include it below. The locations he shows on the G string apply on all strings in the same locations.
An interesting experiment I often demonstrate to my students when introducing harmonics involves placing the side edge of a single sheet of paper at the location of the natural harmonic on E string. This shows you how very lightly you must touch the string. Any more ‘heaviness’ from the finger will not produce the harmonic. It is often difficult to play the fast, heavy bow required to produce the harmonic, with an airy, light fingertip when first trying the harmonics on the violin. When we start experimenting with fingered harmonics, it can further confuse the mind!