The fairly deep blister on the fourth finger of my left hand seems to have resolved itself and started turning into a callus. I have no corresponding callus or blister on my right hand since I nearly never use my fourth finger on that side.
It’s strange though that I have developed no blisters or calluses on any of my other fingers. Only the ring fingers seem to be soft enough to be a problem. I guess the others are used often enough during the day normally that they simply thicken up a bit where the string hits them.
I also want to make a point of practicing rolling chords when there is a fourth between the third and index fingers — when a triad is in third inversion, in other words. That seems a bit sticky. Chords on a harp are easier to deal with when they consist of a high note with a cluster of low notes on the other end of the hand; the piano is exactly reversed in the right hand since that hand is reversed. I think this is why rolling chords neatly when the index finger is closer to the thumb than the middle is a challenge.
There is also the issue of rolling chords in synchrony with a downward arpeggio in the left hand. Upward? Fine. Downward? Yikes.
Many things to learn …