Question

The whitewash on buildings turns yellow with time. How does mixing indigo in lime before
whitewashing help to keep the building white for a longer time?​

Answer 1

Answer:

Whitewash is a very low cost type of paint made from slaked lime (calcium hydroxide) and chalk (whiting). Chalk is calcium carbonate. Slaked lime turns into chalk by reacting with carbon dioxide in the air over several days. This causes crystallization, which binds and strengthens the coating. Various other additives can be used.

Whitewash is also called calcimine, kalsomine, and calsomine. The word 'lime' is used carelessly for quicklime (CaO), slaked lime Ca(OH)2; and 'garden lime' CaCO3

Explanation:

Answer 2

Answer:

Mixing indigo in lime before whitewashing helps to keep the building white for a longer time as it increases the brightness and whiteness of the colour on the surface.    

Explanation:

Whitewashing is the process of applying a base paint of lime or calcium carbonate. It is used to provide a base coat for the actual paint. The lime in whitewash reacts with the air and turns yellow with time.

Therefore, indigo is added to increase the brightness and whiteness of the whitewash.