Need tricky infrared backdrop

[gkuenning]

Hi, all,

I have a somewhat unusual requirement for a research project I'm doing. I need to create a backdrop (roughly 6 feet/2 meters square will do) that is black or very dark in the infrared spectrum, and light or white under visible light. To make matters more fun, I need to do it on the cheap.

We went over to a couple of fabric shops today with a laptop, infrared webcam, and TV remote (for illumination), and struck out. There were lots of fabrics that were the reverse (white in infrared and dark in visible), but that won't work for my project. We also found a number of fabrics that were either light or dark in both spectra, but again that doesn't work.

We haven't yet tried to locate a paint or dye that would satisfy the requirement. We're planning to talk to some chemistry experts and try an Internet search, but it also popped into my head that somebody who does infrared photography for a hobby might have stumbled across an appropriate material.

So, can any of you think of something that looks white to the naked eye but photographs black in infrared?

[Terrywoodenpic]

an Ice rink perhaps

Terry

[SonyaL]

I have seen some good ones on here using a cemetary as a backdrop.

Sonya

[gkuenning]

A clarification: I need something I can use in a studio. So while the thought of ice isn't
completely out of the question, it's a bit high under my current budget.

Also, it's not an issue of things that emit infrared, but rather ones that reflect infrared. So if ice is highly reflective of infrared, it won't help.

Nasty problem, huh?

[rbro]

My experience has been that metals appear dark (cold). Trying to do this indoors might not be possible ( cost?). Point an IR camera at a clear blue sky and it turns out black ( because - I think - you are actually looking into space - and it is cold ). A cloudy sky, on the other hand, will be white - due to the fact that clouds hold more heat than outer space. Maybe just a concrete wall in a basement might work. Just remember -- IR is sensitive to heat, not visible light.:lol:
rbro

[Terrywoodenpic]

A clarification: I need something I can use in a studio. So while the thought of ice isn't
completely out of the question, it's a bit high under my current budget.

Also, it's not an issue of things that emit infrared, but rather ones that reflect infrared. So if ice is highly reflective of infrared, it won't help.

Nasty problem, huh?

Infra red is radient heat...as Ice absorbs heat there should be little reflection. no reflection would be at absolute zero, not quite practical.

Try building a small wall in ice cubes to check it out.

[RossW]

Glass absorbs IR, as do the "greenhouse" gases. How about a big glass panel, or even better, a double-pane glass window/door that you've filled with a gas or water vapor? If it isn't light enough in visible spectrum, put something behind it that is.

In general, you probably want to be looking at plastics and organic polymers if the glass/gas idea won't work for you.

[Jon]

Photographic IR is far away from the "heat" end of the spectrum. Perhaps a few more details about what you're trying to achieve might help.

[gkuenning]

Photographic IR is far away from the "heat" end of the spectrum. Perhaps a few more details about what you're trying to achieve might help.

Sure. As I said, I'm in a studio situation. At the moment I'm using a cheap (free, actually) webcam converted to pick up near-red IR, though I'm planning to switch to a high-quality camera later when my budget increases. I'm illuminating my IR-reflective subject with a strong IR source. I need the webcam to ignore the background, thus the need for "black in IR". The part that makes it hard is that I'm also projecting a visible-spectrum image onto the background, and I need to image to appear bright. So I want something that reflects visible and absorbs IR. I don't care if it's fabric, paint, or something else. Cheap is good, though it would be OK to identify medium-priced substance X and do some tests with a small sample.

[Jon]

So you're looking to photograph the subject's IR response superimposed on a visible-colour back-projecton screen? I'd think that merging a visible back-projection and an IR-illuminated subject would be easier. Get a low output, close-in IR source and inverse square means light levels will fall off rapidly, so it's isolated from any background. Then separately shoot the projected backdrop image and merge them in PhotoShop. Enough separation between subject and backdrop and you might be able to do it in-camera, but try it with back-projection not front projection.