When I started to work on color paper at Kodak in 1971, we were just switching to the bleach-fix process that required Ag recovery be made using Fe cartridges, because the Fe became part of the bleach-fix. Many photofinishing labs were't happy about this means of Ag recovery because the recovered flake Ag from the electrolytic Ag recovery used with the previous process fixer was 'off the books' and 'was their retirement fund'. The Fe cartridge recovered Ag had to go through a refiner and thus was 'on the books' for tax purposes.