I wondered how the original was made. Did they paint the whole thing at once and then pleat it? Or was it made of two paintings that were cut up?

It seems to be much simpler than that; the prisms were solid and removable. So you just put them in a rack so all of one side is flat, and paint directly on them. When that painting is done, you rotate all the prisms to the next side and do the second painting.

https://en.wikipedia.org/wiki/Tabula_scalata