Objects changing colours like a chameleon

Researchers at MIT developed a reprogrammable ink to let objects change colour when exposed to ultraviolet light.

The ink was inspired by the colour changing abilities of the chameleon. Dubbed PhotoChromeleon, the project uses a mix of photochromic dyes that can be sprayed or painted onto the surface of any object to change its colour. The process is completely reversible and can be erased with UV light. The process can be repeated indefinitely.

The paint can be used to customise anything from a phone case to a car. The colour remains even in natural environments.

The project builds off of the team’s previous system called ColorMod. This process uses a 3D printer to fabricate items that can change colour, but had a limited colour scheme and low-resolution results (read more about this process here). The new ink does not have these limitations.

For the paint, the team mixed cyan, magenta and yellow (CMY) photochromic dyes into a single sprayable solution. The researchers are able to control each colour channel through activating and deactivating with the corresponding light sources.

Specifically, they use three different lights with different wavelengths to eliminate each primary colour separately. For instance, blue light would be absorbed by the yellow dye, which is then deactivated. Magenta and cyan would then remain.

After coating an object in the solution, the object is placed in a box with a projector and UV light. The UV lights saturates the colours from transparent to full saturation, and the project desaturates the colours as needed, making the desired pattern appear. If necessary, the pattern can be erased by UV light and the process can start again.

In addition, the team developed a user interface to automatically process designs and patterns that go onto the desired items. The user uploads their design and the programme generates the mapping onto the object before the projector comes into play.

Depending on the shape and orientation of the object, the process takes between 15 and 40 minutes.

Photos: MIT