Slashdot Mirror
Archaeologists Clean Dirty Monuments With Face Packs
Makarand writes "According to this
article on indiaExpress.com
archaeologists at the world famous Taj Mahal (Agra, India) are using
a face-pack consisting of soil, cereal, milk and lime to beautify
the monument. This recipe called 'Multani Mitti', which translates as
'mud from Multan,' is based on a beauty formula from the 16th century and
contains lime-rich clay found in Multan (now a part of Pakistan) which was used for thousands of years as a face-pack by
Indian women. The sticky brown mixture is smeared on the pollution-stained marble surfaces
of the monument and washed off with warm water after 24 hours. Scientists from Italy have shown interest in these face-packs to restore
their marble statues. The BBC News
article says the same thing but
has pictures."
The mud draws out the polluting sulphates and carbonates.
I'd imagine that the active ingredient would be the lime (CaO), which reacts with the pollutants in the following manner:.
Notice that one of the products, CaCO3, is the chemical formula for marble. In a similar manner, the lime reacts with sulfates to produce CaSO4, which would most likely take the form of gypsum, which I'd imagine would contribute to the bright white finish.