I have been 'mixing my own' since I started in 1951 at the school Photo-Soc and the Chemistry Master showed us how to mix our own developers-- then when I got a job in 1959 as a Photographer in the Civil Service Ministry of Aviation I discovered a room there like an 'Aladdin's Cave' of ex- WWII chemicals all dusty !! I told the Boss I could make up D163 print developer for the Senior Photographers who each had a small darkroom, using 'whole plate' glass negatives and he didn't believe me at first but when I showed him I saved the Department a LOT of money and used up the old chemicals from 1945 !!!