The Indian Rupee's banknotes are more than just slips of paper; they are a canvas of history, security, and intricate design. Central to this design is the familiar face of Mahatma Gandhi, the father of the nation. But beyond the portrait lies a fascinating story of special ink, security features, and the Reserve Bank of India's (RBI) commitment to safeguarding the integrity of the nation's currency.

The journey of Mahatma Gandhi's image onto Indian currency began in 1969, with a commemorative series marking his 100th birth anniversary. These early notes depicted Gandhi with the Sevagram Ashram in the background. However, it wasn't until 1996 that Gandhi's portrait became a permanent feature on all legal banknotes, replacing the Ashoka Pillar series. This transition was driven by the need for enhanced security features and the recognition that a human face is harder to forge than inanimate objects.

The portrait of Mahatma Gandhi that graces the banknotes is not a mere caricature but is derived from a photograph taken in 1946. In the photo, Gandhi is seen with British politician Lord Frederick William Pethick-Lawrence. The photograph was chosen for Gandhi's gentle smile, and the portrait is a mirrored image of the cut-out. Interestingly, the photographer and the individual who selected the image remain unknown.

One of the most crucial elements in preventing counterfeiting is the use of specialized inks. While the exact composition of the ink used for printing Mahatma Gandhi's image is a closely guarded secret, the RBI employs intaglio printing for denominations of ₹100 and above. Intaglio printing is a technique where the portrait, Reserve Bank seal, guarantee clause, Ashoka Pillar emblem, and the Governor's signature are printed in raised prints. This raised print is tactile and can be felt by touch, particularly aiding the visually impaired.

In addition to intaglio printing, a colour-shifting ink is used to print the numeral denominations of 200, 500 and 2000. This ink changes colour when viewed from different angles, adding another layer of security.

Beyond the special ink, several other security features are embedded in the banknotes. These include:

• Watermark: The Mahatma Gandhi watermark, with a light and shade effect and multi-directional lines, is visible in the watermark window when held against the light.
• Security Thread: A security thread with inscriptions of "Bharat" (in Hindi) and "RBI" can be seen as a continuous line when the note is held against the light. Some denominations also include the numeral value on the thread.
• Latent Image: When the note is held horizontally at eye level, a latent image reveals the denominational value in numeral.
• Microlettering: Micro-letters are used to print "RBI" on some notes and the denominational value on others, visible under a magnifying glass.
• See-through Register: A part of the numeral of each denomination is printed on the obverse and the other part on the reverse, achieving accurate back-to-back registration, appearing as one when viewed against the light.
• Fluorescence: The banknotes fluoresce in yellow on the reverse and the text will fluoresce on the obverse under ultraviolet light.
• Identification Mark: A special intaglio feature in different shapes for various denominations is present on the left of the watermark window to help the visually impaired.

The RBI's Department of Currency Management is responsible for designing the banknotes, subject to approval from the central bank and the Union government. Section 25 of the RBI Act, 1934, mandates that the design, form, and material of banknotes must be approved by the Central Government after considering the central board's recommendations.

In conclusion, the seemingly simple image of Mahatma Gandhi on Indian currency is underpinned by sophisticated printing techniques and security features. The special ink used for the portrait, combined with other elements like the watermark, security thread, and microlettering, makes the Indian Rupee a secure and resilient currency, reflecting the nation's commitment to integrity and innovation.