Are these tiles laid straight?

Tile with white grout.

Tile with 60% black grout.

Tile with black grout.

This is an illusion pointed out to me by Tom Tompkins of the San Francisco Exploratorium in August, 1998. The walls of the new Exploratorium bathrooms are tiled with this pattern. All three panels above have identical tile spacing. The only difference is the color of the grout between the tiles. Note that if the grout is white, as in the left panel, the tiles appear to be in straight horizontal columns. The "wavy" effect becomes stronger with darker grout.  For my eyes (and brain) 60% black grout creates the strongest illusion.

Below are some photographs of the bathroom wall.

wall1.jpg (40505 bytes)

wall2.jpg (51323 bytes)

wall3.jpg (50056 bytes)

wall4.jpg (36953 bytes)


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