 Claude's principal patent expired in 1932, which led to a great expansion in the production of neon signage.The industry's sales in 1939 were about $22.0 million; the expansion in volume from 1931 to 1939 was much larger than the ratio of sales in the two years suggests.Rudi Stern has written, "The 1930s were years of great creativity for neon, a period when many design and animation techniques were developed.