Here is a UV reactive ink from Noodlers, a UV ink manufacturer for pens. One thing I noticed it is very thin , so it wets the paper more, I think I need a substance that has more UV pigments inside. This is the first UV tests. I want to have at least two inks in QR codes. The reason has to do with a variety of lighting conditions, different inks work better. Low light for example UV is king, but daytime IR absorbing looks grey even in daylight. QR codes can be any color, they operate on principles of contrast. As long as one is brighter than the other is should work.