At this location we received another (by now familiar) purple envelope which looked like this on the outside:

and like this on the inside:

Inside the envelope were 51 slips of paper, each containing a reproduction of a piece of art, usually an oil painting. Each piece of paper was marked with either a square, a circle or a triangle, and each had a unique number printed on it.

Because there are so many files and may take a while to load, I've put them onto three separate web pages. Click on each to see them:

triangles

squares

circles

Solution