Development of a new invisible ink ideal for authenticating documents

Authenticating works of art, certifying documents… There are many applications made possible by the development of a new invisible ink from an inkjet printer and conventional cartridges purchased off the shelf.

At the University of Utah in the United States, a team has succeeded in developing an entirely new type of invisible ink, and this, using only a conventional inkjet printer and cartridges commercially purchased ink. Thanks to this new ink, it becomes possible to embed logos, images or all kinds of information only visible on documents when they are highlighted by polarized electromagnetic waves (microwaves and infrared).

Authenticating documents, distinguishing original works from counterfeits, this technique offers many possible applications at a lower cost.  » We used silver and carbon-based ink to print an image made up of small rods a millimeter long and a few hundred microns wide. By changing the quantity of each ink, the conductivity of the rods is modified. This modification is invisible to the naked eye, but by appropriately illuminating the image, one can extract coded information thanks to the differences in conductivity. says Ajay Nahata of the University of Utah, who participated in the project.

As can be seen in the illustrations, the researchers, to show the principle of this technique, coded several QR codes on the same image, which are displayed in turn as the lighting varies. As they explain in the review Optica, this technique should find applications in the fields of protection and verification of original data, although the technique still needs improvement. They are already working on new ways of proceeding in order to achieve better definition images that can be observed under polarized light in the visible spectrum.

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