Opening a foldformed Rueger fold

I managed to make a nice spiral Rueger fold but whe I open it it
(after annealing) becomes straight and I can’t make the nice spiral
form again becaose the fold is hard. In Mr. Lewton-Brain’s book there
are beautiful spiraled open Rueger folds. Does anyone know why the
folded edge becomes straight and how to open the fold and retain the
curves?

Judith