For over 25 years years I have gazed lovingly at a variation of the bird base (where the 22.5 degree creases are extended right across the paper) that looks like a gemstone. I stare at it, hoping that divine intervention will show me a way to lock the loose flaps together at the bottom with minimal extra work. The current book project on geometry has unearthed the same puzzle, since it’s highly geometric and I have found at least one alternative solution.

The decorations created by Rae Cooker have often used two identical units where opposite flaps interlock simply by sliding into each other. Following this logic, I tried to “invert” the gemstone creases so the angles at the corners instead began from the centre. Lo and behold, the following model delicately came into being, sliding flaps from the outer sheet into pockets on the inner. Not a sturdy “lock”, but sufficient for my needs. As with all elegant designs, it may not be original, but it’s new to me and that’s all I worry about 😉

To give you plenty of clues, here are the two constituent parts…