Geometrix

And here's a stained glass rose for you..

Free-hand, pencil, paper and then Adobe Photoshop.
Looking forward to doing that in glass

Now the Math: Out of 4 triangles made by 2 diagonals of each square, 2 are chosen on the same side of 1 diagonal.
Each of those triangles is divided in half by a line from the opposite vertex.
So series of concentric squares and similar quadrilaterals later we have ourselves a rose.