Educational Toys, Inc., a subsidiary of Topper Corp., produced a set of four Sherlock Hemlock's Hidden Answer Jigsaw Puzzles in 1971. The art was provided by illustrator Jack Davis.
Each puzzle was packaged with a blue transparent "looking glass", which could be used to discover hidden shapes in the picture.
"The Puzzle of the Hidden Numbers"
"The Puzzle of the Hidden Shapes"
"The Puzzle of the Hidden S's"
"The Puzzle of the Hidden C's"
