The main ingredients in whitewash are water and lime, which combine into a thin paste. In some instances, other ingredients are added including binders, alum, carbolic acid, indigo and bluing.
Binders such as salt, flour, sugar, borax, blue and even skim milk may be added to whitewash to help improve the durability of the paint. Alum is used to keep the whitewash coating from rubbing off after it is applied. Because many of the binders used in whitewash have a tendency to yellow over time, indigo or bluing may be added to counteract this affect and help the whitewash maintain a white coloration.