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Does infrared ink exist?

My question is... does infrared ink exist? Also, If you paint your room with a near infrared "color", would you be able to see it differently in a picture taken by a average camera? (just like you can see the IR light in a remote control through a camera).

yes, infrared marked cards, Did you try googling for "infrared ink"?

I did. But the reason why I decided to start the thread is because it doesn't seem to be very common. I have never seen it anywhere. Probably because it is pretty much useless, but it still could be used as a way to kids to play, writing stuff in infrared then finding a way to read it. I have never seen such thing. 

I still am not quite sure what it would look like. Apparently it looks transparent. However, I thought it would look black, because it absorbs all the visible light. Now I want a IR pen.

A pigment does not have to absorb all other wavelengths. If it is transparent all visible wavelengths but reflects IR it would work the same. The usual ink actually absorbs a range of non-visible light, transparent to a wide range, and re-emmits in IR. The effect is flourescent - like when you shine UV on some materials they glow a distinctive color.

Definitions are important. I was using the definition that the stuff I find in my fountain pen or a printer ink cartridge is "ink" ... so "infrared ink" would have similar properties. Blue ink would be any fluid that lets you write in blue... by analogy... Then I checked my concepts by finding out what was being marketed and/or researched under the label "infrared ink". It's not exactly a scientific term.

You could use the subtractive color approach to get an IR image via filters. But for pigments, the subtractive model is only for visible light. That's why the link I gave you only shows visible colors in it. It does not explain inks, it explains how colored inks can be mixed to make other colors. i.e. in the subtractive model: Yellow+Blue=Green, but in the additive model Yellow+Blue=White You seem to be asking for a substance that absorbs all wavelengths except a small range in the infra-red. (Or whatever color you want.) No pigment works like this. Blue ink does not absorb every single wavelength that hits it that isn't blue. If it did, it would get hot. Objects that absorbs every wavelength are called "blackbodies" and they actually radiate light in a continuous spectrum. If they absorbed everything but blue, they's still radiate a continuous spectrum. When something absorbs light, it gets hot. It radiates according to how hot it is. To make a black pigment, you have to get it to absorb as much visible light as you can, are re-radiate the energy outside the visible spectrum: usually this is infra-red. i.e. colors work like they do because the surface does not absorb every other wavelength. Regular colors are only the way they are if you isolate a narrow range of wavelengths (the visible spectrum). Considering that everything warm glows in infra-red, the main issue with making an IR ink is fitting the part of the definition that says you have to be able to write stuff with it. This means it has to be visible against the general IR background, which is why the fluorescent inks are the way to go.

Now, we have know infrared ink is sure have, and can be make on playing cards?  sure, invisible infrared ink can make marked cards.

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