I recently received a box of lenses. I examined each one to determine the lens type and clean them. After unscrewing the outer ring on one of them I found the lenses would not fall out as was typical. Then I noticed that the lenses were set in the tube crooked; they were jammed in place. I was pretty sure this lens was a petzval design but I could not tell for sure. And if the lenses were mounted in a crooked fashion, than they would give odd results. It was difficult looking through the glass to see if there was a ring that separated the elements. So I decided that the lenses needed a little persuasion from the rear to force them out. Repeated pressure applications did nothing. I decided that more force was necessary. I was concerned about chipping the glass around the rim where it met the tube if I did something wrong; but this old glass tended to be rather thick.
So I took a piece of wood to act on the rear of the lens. Tapping on the lens did not budge it, harder tapping did not budge it, but even harder tapping finally got results! As I examined the destruction I noticed that I busted just the inner lens (oh, now I remember, the air spaced elements are not thick like the cemented elements, actually they have rather thin edges). I then was able to confirm that this indeed had been a petzval lens.
I never did budge that crooked outer lens.
If anyone wants a lens tube and mounting ring with two of the three elements from a petzval lens its available for $10 plus shipping.