Please note in the OP that I suggest adjusting the gelatin to 5 - 10%. This can be done before or after the wash. It depends on method of wash and on the amount of dilution given to the original pot by the amount of ammonia used. I used household ammonia in one case and it was too dilute to set. I used 28% ammonia and it was just fine.
There are precise notes on this formula given to my workshop students in their notes.