Indelible ink, which can be applied with a brush, marker pen, spray or by dipping voters' fingers in a bottle, contains silver nitrate. Its ability to stain the finger for a sufficient period of time – generally more than 12 hours – is highly dependent on the concentration of silver nitrate, how it is applied and how long it remains on the skin and fingernail before excessive ink is wiped off. The content of the silver nitrate could be 5%, 7%, 10%, 14%, 15%, 20%, 25%. Indelible marker pen 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 institutionalised.
