I'll be commenting soon. We've just settled into our new place and I'll have a look at the prints in depth this arvo.

Michael,
Thanks for the kind words.
I used a 6x6 glass neg carrier with a 35mm negative. I then used a 4 bladed easel to mask everything but the thin edge of the negative rebate. There is no science involved, just a bit of trial and error getting the borders right.