Photochromic Pigment Experiments
I've been sharing a series of experiments with photochromic pigment online recently and many have asked about what materials I'm using and how the process works. Stay tuned for a more thorough write-up! (and subscribe to my very infrequent newsletter if you want to be updated about this sort of thing) Here's a quick description of my process so far:
The big idea: I'm using a UV led light to "paint" onto paper and other objects that are covered with a photochromic pigment mixture. This is not a permanent process. The image lasts for a minute or so before fading away. (this is kind of how transitional glasses lenses or "invisible ink" work they change color temporarily when exposed to UV light like the sun)
Here are some suggested steps to follow if you want to try this out:
Order some photochromic pigment! I used this one: https://atlantachemical.com/sun/wv_pp_sun.html? .You can see that they have other color options, like a pigment that goes from pink to blue. I picked the white to violet one because I wanted the pigment to blend in with the white paper when it wasn't activated. I think I ordered the 20g container but I only needed a tiny amount to cover my paper.
Mix the pigment with something like paint or glue and apply it to the surface of your choice. You might need to do some experimenting here. I used white Elmer's glue (about 1/4 cup) and mixed it with about 1/4 tsp of pigment powder. This was more than enough to cover one sheet of paper and a plastic water bottle. I had a lot leftover. I used a regular foam brush to apply the glue/pigment mixture. I used glue because I thought that it might dry clear, but it didn't (probably because the pigment itself has an opaque white color ).
Let your painted surface dry
In the meantime, find a UV LED light or UV pen. I had some small UV LEDs handy but I found that when they were powered by a small coin cell battery, they weren't quite bright enough to make a dramatic color change. Instead, I ordered a pen like this. This works well, but I'd like to find a slightly smaller pen as well. You can also use the sunlight! I did some experiments where I tried to "catch" patterns coming in through my windows.
Now you're ready to experiment. I'll share some of the prompts I tried out below. I also think this is a good way to introduce the idea of how processes like photo emulsion or cyanotype photography work.
Prompts:
Experiment with found objects to see what kinds of patterns and shapes they make. Try creating new shapes by "exposing" the materials repeatedly.
Create customized "stamps" or "stencils" by drawing onto clear materials, like transparency paper. I used a china marker to draw on the transparency because they are waxy and opaque. You can place the transparency on top of images or patterns to trace them.
Print your own "negatives". I printed images I found in the Smithsonian's open collection. I had to do a little bit of photo editing to make them work the way I wanted them to (so that they print a positive version of the image on my paper). I converted the image to black and white, inverted the colors, and played with increasing the contrast a little bit. Then, I printed the images onto my inkjet-friendly transparency paper.
"Catch" patterns made by the sun, like this pattern made by the light coming in through my blinds
What's next:
Stay tuned for better documentation and more info/prompts
Some of you have asked if there's a way to make the process permanent. I'm currently experimenting with cyanotype materials to see if the same prompts and materials I shared here might work well with the cyanotype process.