A toy for re-creating the Droste effect from Escher’s Print Gallery.
Inspired by M. C. Escher’s lithograph Prentententoonstelling (1956) — Dutch for print exhibition. The name tententoon is a playful contraction of that title.
Escher left a famous white blot at the centre of the print: the spiral was so tight that he couldn’t draw it any further. In 2003, Hendrik Lenstra and Bart de Smit worked out the underlying math — a conformal map built from complex exponentials and logarithms — and completed the picture by computer.
In 2026, Grant Sanderson (of 3Blue1Brown) published a beautifully animated video walking through the paper. Highly recommended — it is the clearest tour of the math behind this toy.
This editor is a small interactive take on that idea: pick a rectangle inside any image and watch it spiral into itself forever. (Complex numbers are fun. So are logarithms.)
Tententoon sits at a different register from the other projects on this page. It is not a client engagement, nor an open-source product. It is a small toy Silvio built around something that was dear to him — the math behind Escher’s Print Gallery, a painting that has hung in his room since he was a kid. Two things brought him back to it recently: his son’s homework on Escher’s work, and the 3Blue1Brown video above on the math underneath the print. The toy is what came of it — the kind of fun he often has around math and educational ideas, usually with his son in mind.
