Photometric measurements on butter, butter colour and carotene. Standardisation of butter colour
Milchwirtsch. Forsch 17: 72-86
Three chemical and two vegetable colouring materials were examined in a step photometer using 8 different filters and showed marked differences in concentration, but only slight differences in colour composition. The chemical colouring materials were much superior to the vegetable ones in their resistance to the action of light: an oily solution of carotene was intermediate.