No surprise that concave cuts in ceramics are a high stress, so Kite and Dart tiles don't work very well (the dart is likely to crack). Same is true for the Turtle, Hat, and Spectre.

Rhombus tiles are everywhere convex, and the P3 Rhombus tiles are easy to cut in a diamond saw (or even a snap-cutter). With a diamond band-saw, it's possible to make Penrose rhombs with curved (parabolic) edges.

But cutting tiles from stock field tiles produces sharp surface edges -- you don't want these as bathroom floor tiles. Also, you waste a lot of the field tile as scrap. To get "friendly" tile shoulders, I'm experimenting with making Penrose tiles directly from high-fired porcelain clay.

> In each center of an hexagon you can have any of the 12 possibilities:

> Any of the 6 rotations of the Hat

> Any of the 6 rotations of the anti-Hat

For this claim to hold, it must be the case that a Hat (or anti-Hat) occupies the same area as a hexagon. But they don't: a hexagon is made of 6 kites, while a Hat is made of 8. So, some hexagons must contain no corresponding (anti-)Hat -- specifically, for every 8 hexagons, there must be 6 (anti-)Hats.

This seems to complicate the SAT formulation. But could the fix be as simple as adding a 13th possibility, "No hat at this hexagon centre occupies more than half of its kites"? Or are additional constraints needed?