Context: 

With the first phase of voting for the 2024 Lok Sabha elections beginning on April 19, the classic symbol of Indian polls is visible everywhere – a left hand with only its index finger extended, marked by a purple-black indelible ink.

Background:

Devised as a method to prevent a person from casting more than one vote, the indelible ink has been used for decades in India. It has also travelled to other parts of the world to help in conducting elections.

About the Indelible ink used in elections: 

1. The Section 61 of Representation of the People Act (RoPA) of 1951 mentions the ink. It states that rules may be made under the Act “for the marking with indelible ink of the thumb or any other finger of every elector who applies for a ballot paper or ballot papers for the purpose of voting at a polling station before delivery of such paper or papers to him.” Why papers? Because before EVMs, ballot papers existed at polling stations. They contained the list of contesting candidates alongside their party symbols and names. Voters had to mark their preference on the paper and then drop it in ballot boxes to vote.
2. Indelible ink contains silver nitrate. It is a colourless compound which becomes visible when exposed to ultraviolet light, including sunlight. The water-based ink also contains a solvent like alcohol to allow its faster drying.
3. Silver nitrate is an inorganic compound with the chemical formula AgNO3.The higher silver nitrate’s concentration, say around 20 percent, the higher will be the ink’s quality, according to a report from the United Nations Development Programme. For up to 72 hours after application it can remain resistant to soap, liquids, home-cleansing, detergents, etc.
4. The indelible ink was first manufactured at the ECI’s request by the government’s Council of Scientific & Industrial Research (CSIR). It was later patented by the National Research Development Corporation (NRDC), New Delhi.
5. Mysore Paints & Varnish Ltd. has been licensed to manufacture the ink and has been in the business since 1962. Earlier called Mysore Lac & Paint Works Ltd, it was established in 1937 by Nalwadi Krishnaraja Wodeyar, then the Maharaja of Mysore. This Karnataka Government Undertaking is the sole manufacturer of the ink in India.
6. Today, once a voter has her credentials checked at the polling booth, and before she casts her vote by pressing a button on the Electronic Voting Machine (EVM), the indelible ink is applied on her finger. This has been the case for decades, although the mode of voting has changed.
7. Currently, the indelible ink is exported to more than 25 countries that include Canada, Ghana, Nigeria, Mongolia, Malaysia, Nepal, South Africa and the Maldives.