Sanborn encrypted the text by placing a physical copper stencil over the K1/K2 matrix. This stencil acted as a "Fractional Grille" or "Shadow Mask". Because he scrambled the text into blocks of 7, the stencil had 7 distinct reading holes.
For Col 1 of a block, he looked through Hole 1. For Col 2, Hole 2, etc. Below, you can click through the 7 holes. The Left Canvas shows the Intended Plaintext letter he was trying to trace. The Right Canvas shows how the geometric shape of the curved sculpture warped the light, projecting it to the Calculated Ciphertext letter!