There’s usually many possible ways to solve a problem but they get narrowed down based on other constraints.
A few things I have found to solve the issue of using a material or dye that is easy to see under infrared light but hard to see under visible light are infrared paint and retro-reflective materials. Infrared paint looks black under visible light but infrared light passes right through it. It’s often used for security purposes and is quite expensive. http://www.anytimesign.com/infrared_magic_black_ir_transparent_paint.htm
Retro-reflective materials come in many forms such as pigments, to fabric to beads. Retro-reflective materials bounce light back to its source. Its often found on the reflectors of bikes, shoes and jackets so cars can easily see people at night. In the dark, retro-reflective materials won’t be seen but they’ll bounce infrared light back at the source. This was actually quite blinding to the camera as seen below.
The retro-reflective pigment in a bag in a cup. It’s like a fine powder and can get quite messy and hard to clean up if I spilled it.
I went around the house also looking to see if there was anything that came out white under the night vision goggles but was black during the day. Most materials were black under visible and infrared light but I stumbled upon a receipt that I knew had letters printed on it but was clearly blank under the NV goggles.
I wrote the HELLO with a pen to show regular ink still is black under infrared but the print on the receipt disappeared.
Turns out receipts are printed not with ink but using a precision heated head that activates the dye on the receipt paper. A couple seconds over an open stove top and the whole receipt turned black. But it was completely white to the night vision goggles. I had finally found a solution to my biggest problem!
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