Fredrik Owesen did some reverse-engineering of the folding techniques mastered by Yuko Nishimura, a long-time favorite of mine. (if you like pleating and tessellations, Nishimura is probably also a favorite of yours, too!)
Fredrik gave a little description of how to accomplish this type of folding:
I’ll try to write up some sort of how-to, although I suspect they tend to be confusing.
I’ve grown pretty lazy in terms of folding methods lately, so this will be based on that. You begin by drawing the crease pattern on the sheet you want to fold, using a sharpish ballpointpen, one without ink or a color matched to the paper is good. First lines divide the sheet in long rectangular lines (1). Turn the sheet, then using some sort of curved guide (found a cheap flexible ruler well suited for the purpose), fill in the curves that go between the lines from the previous step.
Use the lines you just drew, both curved and straight, to mark up a grid by forming lines perpendicular to these. The curved lines will give the grid some unevenness, but when forming the grid treat them as straight lines, ignoring the spacing. Turn the sheet over and create a similar grid 50% ofset from the other.
Using these marks it is easy to fill in the zigzag pattern, mountainfold on one side, then flip the sheet over for the valley folds. Collapse it into shape when all the creases are there.
I’ve long wanted to fold something like this, so thanks for the hints, Fredrik. Now to sit down and give it a try…