Electoral ink, indelible ink, electoral stain or phosphoric ink is a semi-permanent ink or dye that is applied to the forefinger (usually) of voters during elections in order to prevent electoral fraud such as double voting. It is an effective method for countries where identification documents for citizens are not always standardised or institutionalized. The most common election ink used worldwide was invented by Filiberto Vázquez Davila, a Mexican biochemical engineer.
Indelible ink is used as an effective security feature to prevent double voting in elections or the case may be (like Indian government has structure to use this ink for curbing the corruption and double entry in demonetization). Ink is normally applied to the left hand index finger, especially to the cuticle where it is almost impossible to remove quickly. Ink may be applied in a variety of ways, depending on circumstance and preference.
This ink typically stays on skin for 72–96 hours, lasting 2 to 4 weeks on the fingernail and cuticle area. The election ink used in India puts a permanent mark on the cuticle area which disappears only with the growth of new nail. It can take up to 4 months for the stain to be replaced completely by new nail growth.
Electoral stain typically contains a pigment for instant recognition; a silver nitrate which stains the skin on exposure to ultraviolet light, leaving a mark that is impossible to wash off and is only removed as external skin cells are replaced. Industry standard electoral inks contain 10%, 14% or 18% silver nitrate solution, depending on the length of time the mark is required to be visible. Although normally water-based, electoral stains occasionally contain a solvent such as alcohol to allow for faster drying, especially when used with dipping bottles, which may also contain a biocide to ensure bacteria aren’t transferred from voter to voter.