Preliminary base (square base)
The preliminary base, also called the square base, is a traditional starting shape in which a square collapses into a smaller square with four flaps and all the open corners at one end.
With the colored side up, crease both diagonals; turn the paper over and crease both midlines. Now hold the sheet so a corner points toward you and bring the other three corners down to meet it, letting the paper fold along the existing creases. It flattens into a square one quarter of the original area, open at the bottom.
If the paper resists or wants to form a triangle instead, the diagonals and midlines are probably on the same side; they must be on opposite sides. Sharpen all creases before collapsing. The preliminary base leads straight to the bird base and is the first milestone in the Paper Crane.
