Trying to avoid buying expensive material. Fail and semi victory.
The corner holders on a piece of cardboard were a fantastic fail. Then i took the magnets from my fridge and i think it’s the solution. They only stick to the spring holders supposed to maintain the plate in place, they are very small so you can easily open and close the plate. I should find the way to make the 120 film as plane as possible with these, but i do think i can have nice results without buying an expensive roll film back for 6x13 plates!