TN, West Bengal Polls: The Science Behind The Ink That Stops Double Voting

As polling unfolds across Tamil Nadu and West Bengal on April 23, 2026, millions of voters are taking part in an exercise that rests on more than just ballots and machines. At every polling booth, after a vote is cast, a small purple mark is applied to the left index finger. It may appear routine, but this mark is one of the most critical safeguards in the electoral process, ensuring that no individual can vote more than once.

The indelible ink used for this purpose is not ordinary. It is a carefully formulated chemical solution, primarily based on silver nitrate, designed to leave a lasting imprint on the skin. When the ink is applied, it reacts with the salts and moisture present on the surface of the skin to form silver chloride. This compound then darkens upon exposure to sunlight, making the mark more visible over time. What makes the ink particularly effective is that it does not remain on the surface. Instead, it penetrates the outer layer of the skin and binds with proteins, which means it cannot be washed away with soap, water or common chemicals.

The stain gradually fades only as the skin naturally sheds and regenerates, a process that can take several days to weeks depending on the concentration of the ink. This ensures that once a person has voted, the mark remains long enough to prevent any attempt at repeat voting, even if they move to another polling station or constituency.

Its role becomes even more significant in elections like those underway today. Tamil Nadu is voting in a single phase across all 234 Assembly constituencies, requiring seamless management of a vast electorate in one day. West Bengal, on the other hand, has begun a multi phase election, with the first phase covering 152 seats and subsequent phases scheduled days apart. This gap creates the possibility of individuals attempting to travel across regions to cast another vote. The indelible ink acts as a simple yet highly reliable barrier against such attempts, functioning as a physical and visible record that cannot be easily altered or removed.

The ink itself has a long and well established history in India's electoral system. First introduced during the 1962 general elections, it was developed by the National Physical Laboratory under the Ministry of Science and Technology. Today, it is manufactured exclusively by Mysore Paints and Varnish Ltd, a government owned company that remains the authorised supplier. For elections of this scale, involving over 5.7 crore voters in Tamil Nadu and more than 3.2 crore in West Bengal's first phase alone, lakhs of vials are produced and distributed to polling stations across both states.

In an era where elections are increasingly influenced by digital systems, data security concerns and misinformation, the continued reliance on indelible ink highlights the value of a solution that is both simple and effective. It requires no electricity, cannot be hacked, and works uniformly across urban and rural settings alike.

From first time voters to senior political leaders, every individual who casts a vote today leaves the polling booth with the same unmistakable mark. By the end of the day, as voting concludes in Tamil Nadu and the first phase wraps up in West Bengal, that small purple stain will stand as proof of participation and, more importantly, as a guarantee that each vote has been counted once, and only once.