Little is known about Koegel's early years, except that he served as a Benedictine monk in the Beuron Cloister, Baden-Württemberg, Germany. Koegel employed chemical means and photographic methods to bring out the old writings, developing the use of ultraviolet light, which caused the erased writing to fluoresce and thus show up on photographic negatives.
Gustav used diazo dyes as well and became an authority on this light-sensitive material. From 1916 to 1921 he perfected a diazo paper developable by exposure to ammonia vapor and, by 1921, had interested Kalle & Co. A.G. at Wiesbaden-Biebrich in the process. The diazo copying paper they marketed four years later, the first to compete with blueprint paper, was named Ozalid - the reverse spelling of "diazo" with an added "1." Koegel later withdrew from the cloister and continued his photochemistry research at Kalle & Co.