The science of indelible ink

As questions are raised about the efficacy of the ‘indelible ink’, more popularly known as voter’s ink, used in the general elections, the Council of Scientific and Industrial Research which developed the ink has come out in defense of its product.

“We developed the ink in 1960s and transferred it to Mysore Paints and Varnish Limited, which has been the sole supplier ever since. Billions of people have voted in the general elections all these years and every time, the ink was used. There are no grounds for doubt. It has stood the test of time. That is its truest test,” said Dr Shekhar Mande, Director General, of India’s premier R&D organization.

He said it was ‘unlikely’ that the ink would wear off within few hours, as alleged by some voters on social media. “We have not directly received these complaints, but it is highly unlikely. We stand by, what we have developed.”

The purple-coloured ink is applied on the left-hand index finger of the voter in a polling booth. Once applied, the ink cannot be removed by any chemical, detergent, soap or oil for several months. The ink is used in all elections across the country.

According to reports, the Election Commission ordered 26 lakh bottles of indelible ink for the ongoing Lok Sabha polls. In 2014, about 21.5 lakh phials were bought.

In 1962, the Election Commission, in collaboration with the law ministry, National Physical Laboratory and National Research Development Corporation, made an agreement with Mysore Paints, a Karnataka government entity, for supply of indelible ink for Lok Sabha and assembly elections. Since then, it has been supplying the ink for all elections in India.

Mysore Paints also exports indelible ink to more than 30 countries across the globe.

This year, during the first and second phase of the general elections, some voters on social media, alleged that they were able to wipe out the ink within few hours after they cast their vote. The voters also shared pictures on social media.

"Its main constituent is silver nitrate, which reacts with the skin protein and makes a strong bond. It leaves a dark stain, which remains for several days to even weeks, but will not harm your skin. The mark will wear off only when the old skin cells begin to die and are replaced by new ones," said Dr D K Aswal, Director, National Physical Laboratory.

Silver nitrate used in the ink is caustic to skin. The ink dries out in less than 40 seconds and leaves a dark stain behind.

However, the strength of the stain depends on the quantity of the silver nitrate used. According to the manufacturers, the concentration of silver nitrate ranges from 7% to 25%, but the exact composition cannot be disclosed due to proprietary concerns.

Scientists have emphasized that there are certain essential pre-conditions to applying the ink.

“It’s applied on the index finger of the left hand, across the skin and nail, after which the voters casts his/her vote and exits the booth after adequate checking. This process is long enough to allow the ink to dry, so it cannot just wear off. But, it might be the case, that some individuals applied a greasy material to prevent its reaction with the skin,” said the senior scientist.

Greasy materials like petroleum jelly could act as a barrier to the skin.

According to officials, the ink undergoes several tests before which it’s supplied to the states. “EC picks up random samples during the election process and sends it for testing to our laboratory, because there are always concerns regarding any duplicity or any mischief during the transit. We have been submitting our regular reports to EC after each tests,” said Dr Aswal.

The laboratory is now working on developing the invisible ink, which when applied would not leave a dark stain but will be visible under amber light. The technology would take a few years before its ready for use. End