Invisible Ink: What is it and Where it is Used

In a previous article, we took a look at inks that change colour when introduced to certain temperatures, known as Thermochromic Inks. But, did you know that there are also inks that are designed to only be seen under Ultraviolet light?

These 'secret inks' are really useful when protecting products with secret information, such as medication packaging or logistics documents. So, how do these inks work and where are they used? Let's take a look.


Light-activated inks work because they contain substances that glow under different types of light but remain invisible to the naked eye. Strictly speaking, dyes and pigments are what give ink its colour in most applications, and the same dyes and pigments can be formulated to be naked to the visible eye. The microscopic particles responsible for this, taggants, are added to the ink as they react to the proximity of a unique “reader” or verifier.

Because these 'invisible' inks do not have colour by design, most applications of such inks contain a taggant that reacts with a specially designed camera, light, or scanner. For example, in invisible security ink, the taggant is developed to react only with equipment using a UV, infrared, or near-infrared light at a specific wavelength. Clever, right?


We have already mentioned some applications for UV-readable inks, but there are quite a wide variety of industries that make use of this ink, such as:

  • Pharmaceutical Manufacturing - prescription medicines and packaging
  • Luxury Goods - such as watches and jewellery
  • Concerts & Events - tickets and hand stamps
  • Lottery Tickets
  • Vouchers and Coupons - authenticity marking
  • Marketing Tracking - numbering documents to identify demographics


The classic method among secret inks works because the writing only becomes visible when the paper is heated. However, it remains visible forever afterwards, because the heat of the ink triggers a chemical reaction with the paper. Invisible UV-readable inks offer a great solution for traceability in manufacturing; in the event of sudden production errors, LOT or batch numbers enable the manufacturer to search for the cause. The ink remains invisible except when placed under a UV light.

Traditionally, information is printed directly onto packaging using coloured inks. However, this unsightly marking in the form of a data matrix code or series of numbers can disrupt the appearance of a product. Especially with small or all-around visible products, UV-readable inks provide a means of coding and marking products without altering the appearance of aesthetically designed packaging.

Forgery and counterfeiting are becoming increasingly important to government and business professionals. UV-readable inks help to address counterfeiting, providing invisible authenticity markers for anything from banknotes to luxury goods to vouchers.


We hope that this blog has helped to shed some light on UV-readable inks and their uses. Here at Needham Ink Technologies, we have decades of experience in providing reliable coding solutions and consumables you can rely on.