Note the unique folded squares that make up the frame.
|In two pretty papers, set in opposite directions|
|Start with a square, and fold in half, then crosswise each way to look like this.|
|Push sides in on the folds to form a triangle.|
|It will look like this. (The end corners actually match; perspective is distorted in this photo).|
|Then turn one top corner to the middle....|
|..... then the other corner likewise, and you are done. Now make many more of these and create a border.|