After World War II, the wood jigsaw puzzle went into a decline. Rising wages pushed up costs substantially because wood puzzles took so much time to cut. And as prices rose, sales dropped. At the same time improvements in lithography and die-cutting made the cardboard puzzles more attractive, especially when Springbok introduced high quality reproductions of fine art on jigsaws. In 1965 hundreds of thousands of Americans struggled to assemble Jackson Pollock's "Convergence," billed by Springbok as "the world's most difficult jigsaw puzzle."