The Cronak process is a conventional chromate conversion coating process developed in 1933 by The New Jersey Zinc Company.
[1] It involves immersing a zinc or zinc-plated article for 5 to 15 seconds in a chromate solution, typically prepared from sodium dichromate and sulfuric acid.
[2] The process was patented in the United States on March 24, 1936 with USPTO number 2,035,380.
[3]