My son learned about infrared and ultraviolet colors, and how flowers used them to attract insects. I mentioned that people can use them too, but you need special goggles or lenses to see something marked with infrared paint. Then my son asked me:
"when you open a gallon of infrared paint, what does it look like inside? Is it invisible, do you see an empty can? It's solid and not clear, but you can't see it, so what happens?"
Any thoughts?
I assume it looks like whatever color the base opacifier is - probably TiO2, so white. Or if it is a neutral base - clear - it looks like olive oil, basically.
Yes, perceived color is about what color a surface or object reflects from ambient light (e.g. sun or room lighting). Clearly, since it is infrared paint, that part of it will play no part in what it appears to be in the human visible spectrum. As noted above, it's whatever else it is made up of, is what it will determine what it looks like.
Of note of course is that heat radiation is also infrared, so determining what is the result of IR reflection from the paint and IR radiation from the heat might be an issue.
An IR paint is probably some bold color to make it obvious while applying it and then dries to clear, if that is the requirement.
So, green paint is green because it absorbs light in the green spectrum. Red is red because it absorbs light in the red spectrum. Black is black because it absorbs all light. White is white because it absorbs no colors. IR paint would have to absorb in the IR spectrum.
I also agree that it would look like whatever the base is.
Dr. Hess said:So, green paint is green because it absorbs light in the red & blue spectrums. Red is red because it absorbs light in the blue & green spectrums. Black is black because it absorbs all light. White is white because it absorbs no colors. IR paint would have to absorb in the IR spectrum.
I also agree that it would look like whatever the base is.
Dr. Hess said:So, green paint is green because it absorbs light in the green spectrum. Red is red because it absorbs light in the red spectrum. Black is black because it absorbs all light. White is white because it absorbs no colors. IR paint would have to absorb in the IR spectrum.
I also agree that it would look like whatever the base is.
That's pretty much it. Different bases show reflect differing amounts of IR too. The base pigments are relatively recent developed as an attempt to fight "white blight" while improving the thermal efficiency of what they're applied to.
I always thought that objects appear to be the color that they reflect, ie not absob, in the visible spectrum. It's been a long time since I needed that info, so I may be incorrect. In that case of IR, since that part of the spectrum is not visible to the naked human eye, the paint would appear as whatever the base color reflects.
Maybe I have that backwards. Where's our physicist?
Dr. Hess said:Maybe I have that backwards. Where's our physicist?
Something looks green because your eyes are detecting green light. That means the object in question is either emitting only green light (like a green LED would) or it's reflecting green light emitted by something else. If that something else is emitting white light, then to look green it has to reflect the green and absorb everything else.
Yes, thanks. I also talked with my physicist. Black absorbs all, white reflects all, green (paint) is absorbing everything except green, which it is reflecting back to you. A green filter on a light is passing green but absorbing everything else. An IR paint that showed up in IR would be reflecting IR back at you. Not to be confused with an IR absorbing paint that would hide you in IR.
It's not paint, but in the case you you know about it, google-fu vantablack 'cause it's cool.
I was a thermographer and I'm not sure what "infrared paint" you're talking about.
There are paints that are opaque in to the eye but transparent to a thermal imager. They are sometimes used to mask markings. Magic Black is one.
There are paints that are highly reflective to infrared radiation (low emissivity = high reflectivity to infrared). Shiny metallics, for example. Those can make it difficult to get an accurate temperature using an imager or infrared thermometer. Gotta learn some tricks of the trade to do that.
Paints, coatings, and stickers with high emissivity "show" the temperature of the body much better. I've even sprayed foot powder on things (nice and flat, easily removed, known emissivity) to get a good reading.
Emissivity example. Here's a stainless steel teapot, boiling and whistling when the shot was taken. The polished surface has a low emissivity, and indicates 96F even though it's around 200F. (The imager was set with a default emissivity of 0.95, an "ambient" or reflected temperature of 68F, at a distance of a few feet) The square in the middle is a piece of black tape of known emissivity (e=0.96, iirc), showing a temperature much closer to the expected boiling point. The heating element (very red) was out of range for the camera settings because I didn't care how hot it got.
Think about that when you're using your HF IR temp gun to check temperatures on your shiny aluminum oil pan. It's easy to fool yourself.
Wow, very enlightening. The paint in question was theoretical, my 6 year old just came up with it, a basis in reality is not a requirement for any of his questions.
There is a new 'paint' process Toyota has come up with that looks iridescent blue (like some butterfly wings), but has no actual color when looking at the raw materials. It is a structure that works with interference effects to produce a blue 'color'. They worked pretty hard to get it from 16 steps to 7 for a very limited and expensive option on some of the top tier cars.
So can I take this in a different direction?
What would our planet look like if our sun were infrared instead of yellow?
To us or to something evolved there that was able to see in the infrared spectrum?
I've been watching a lot of space documentaries lately, and while infrared stars do get some coverage, they don't even do artists renderings of what things would look like under such a star.
In reply to RevRico :
I'm going to guess that it would just be dark to us, since we wouldn't see the light, but that guess is based off my last physics class in 1978.
In reply to Streetwiseguy :
I'm thinking we would have evolved by now to see infrared so we really wouldn't notice anything different.
An object has a color because it absorbs everything except that color.
So theoretically, IR paint would look black, but in truth it would have some color ranging somewhere from grey. Nothing is perfect at absorbing all other colors. If you have a black panel and shine a red light on it, it will reflect some of the red.
In the same way, IR should absorb everything except IR. Since we can't see IR, it would theoretically absorb all of our visible spectrum and look black. Since nothing is perfect, it will likely have random reflections of other colors and appear grey, brown, or something else.
Now, if the pigment is transparent, it will likely appear clear smoke-grey. More pigment would likely make it more and more filtering like welding goggles. They look black until you have a bright enough light.
In reply to Stampie :
I left evolution out of the equation. I pictured travellers, not natives.
Dr. Hess said:So, green paint is green because it absorbs light in the green spectrum. Red is red because it absorbs light in the red spectrum. Black is black because it absorbs all light. White is white because it absorbs no colors. IR paint would have to absorb in the IR spectrum.
I also agree that it would look like whatever the base is.
That's backwards.
RevRico said:What would our planet look like if our sun were infrared instead of yellow?
Our sun radiates in all sorts of "colors". Some we can see, some we can detect, and a lot goes zipping by and through us with no notice. Oddly enough, the sun is an almost perfect BLACK BODY, being opaque and non-reflective. Its radiation is due to its temperature.
Way too much physics for this early in the morning.
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