Indelible ink’s new challenger: invisible ink

But it may not find immediate application, given India’s long-drawn election process

Now you see it: ‘Invisible’ ink glows, at right, under a particular ultraviolet frequency

Indelible ink, the purple stain that billions of Indians show off during elections, may face an invisible challenger in the near future. The Delhi-based National Physical Laboratory (NPL), the creator of indelible ink, has a new concoction that, when applied on the finger, doesn’t leave a trace — it merely glows a bright orange when a low-intensity beam of ultraviolet light is shone on it.

The NPL prepared the ‘invisible ink’ as part of a pilot project mooted by the Mysore Paints and Varnish Ltd. (MVPL). “The MVPL discussed with us the development of such an ink for use by a client [country] in Europe,” said Dinesh Aswal, director, NPL.

The MVPL, a Karnataka government company, has a monopoly on the manufacture of indelible ink since 1962, and is a major supplier to the Election Commission of India (ECI). It also exports the indelible ink for elections in other countries. C. Hara Kumar, general manager, MVPL, said the ‘invisible ink’ was only at the discussion stage, and nothing had been firmed up.

The indelible ink was formulated as a deterrent against voting twice. But strangely enough, voters in some countries found the stained finger rather unseemly. “In India, we are proud to display our voter’s ink, but apparently in some countries people don’t want to display such a mark. So MVPL asked us if there was a solution,” said Mr. Aswal.

Organic-inorganic mix

The NPL’s invisible ink, however, wouldn’t be of immediate use to the EC. “The current formulation can’t be used for Indian elections as they are spread out over many weeks. We would need a different formulation,” said Mr. Aswal. He described the chemical — a transparent liquid — as an “organic-inorganic” mixture that was biodegradable and could be washed off in 48 hours.”

The ink works on the well-known principle of fluorescence — certain materials emit a characteristic glow when exposed to ultraviolet light. The NPL ink, however, glows only when exposed to a narrow band of frequencies of ultraviolet (UV) light. “Commercial UV markers or inks respond to a very broad spectrum of UV light. So, along with the ink, we’ll supply an inexpensive LED (costing no more than ₹30) that would emit a specific frequency of UV,” said Mr. Aswal. The NPL’s invisible ink experiment is linked to a larger project of creating security inks that could be used to make bank notes and documents, such as passports, more secure.