I realize absolutes are extremely rare, if not impossible, to obtain in the natural world, but how close could we get to creating an absolute black pigment. That is, a paint or coating we could apply to an object that would reflect back as little as possible of the visible spectrum?
What about other forms of EM radiation?
I imagine painting an apple with some absolute-black™, and rather than looking like an object I can pick up, it looks like an apple shaped hole (albeit, a hole that casts a shadow).
Blackest substance known to man. It’s main use is a coating for the interior of telescope tubes. It’s composed of nickel and phosporus alloy, with a specially pitted surface. Prior to this, I believe carbon black, also known as lampblack, was the champion.
I’m not sure it would look like a hole; I think it would look like a black object; difficult to focus upon and difficult to determine shape; ‘itchy’ to look at, if you like (possibly causing the same kind of visual discomfort that you can get by trying to study a deep cobalt blue object in twilight conditions, only more so).
The reason I think this is that holes seldom actually appear black a hole in the ground, for example, is a darker shade of the colour of the surrounding terrain; in fact it could just as easily be argued that we are only able to perceive holes as holes because of reflected light from parts of their inner surfaces.
Right. I was just trying to imagine a real world object that didn’t reflect any detectable light back to the naked eye. ‘Itchy’ is a perfect way to describe the way your brain would try to grasp what you were looking at. I think it would be very compelling too.
And thanks Q.E.D. for the link. Expensive stuff! I wonder what sort of other practical applications it could have? And I’d love to see it in person. Mmmmm, velvety.
Just wondering - is there such a thing as “pure white”? A surface that reflects all the light shining on it is “silver” rather than “white”, and when it comes to light, we have colour temperature to deal with.
Can a non-luminous, non-reflective surface actually be white, as opposed to very light blue, grey, etc?
I’m not sure that a silver-colored object (as opposed to a mirrored surface) actually reflects more light than a white object.
A perfect mirror would reflect back all the light that hit it precisely according to the laws of incidence and reflection.
White objects reflect back a large proportion of the light that hit them but scattering the light at different angles. I’m not sure of the exact scattering pattern, but theoretically I think you could have an object that scatter-reflected ALL the light that hit it, which would qualify it as purely white to me.
In regards to your last question… sorry for being so nitpicky, but what do you mean by non-reflective? Objects that do not reflect back any light that hits them are not any color at all… they’re black. See the rest of the thread for more details. (And why something perfectly non-reflective doesn’t exist any more than something perfectly reflective.)
Leaving that out, yes, non-luminous non-mirrored objects can be white instead of say blue or green. Though it does get a little tricky until you agree on definitions, especially with white versus gray.
Of the pure metal surfaces, aluminum is the reflectivity king. On its own, when highly polished, it has a reflectivity better than 90%. This can be drastically improved with the addition of various enhancement coatings. Enhanced aluminum is the first choice for first-surface astronomical mirrors in the visible spectrum, having an average reflectivity better than 95%. For specific wavelengths, mirrors can achieve better than 99% reflectivity.
Just came across this article and it reminded me of this thread I OP’d. Interesting read. Not sure if it’s a different process than the article in Q.E.D.'s post, but the process works on all metals, not just nickel.
The article seems to describe a product or method of obtaining, for all practical purposes such a coating.
Like the persuit of ‘perfect’ sound reproduction, it’s all in the ear or rather in this case the eye of the beholder.
Perhaps very sensitive photo detectors could tell the difference or improvement.
For visual effect the immense empty space of a large cavern in the heart of the earth, at Mammoth Cave KY, with NO lights, appears blacker than one can immagine.
A small hole in an otherwise enclosed large cavity is the blackest black you can make, especially if the cavity is also painted black in its interior. The reflectivity of the hole varies as the inverse square of the ratio of its radius to the cavity’s radius. See “ideal blackbodies”. It works in the visible just like in the IR.
Silver is the whitest metal when we compare shiny ones. Aluminum is preferred for mirrors because it’s easier to keep from corroding - silver forms dark halides easily (that’s why you have to polish silverware).
Mirrors and snow both reflect almost all the light. The difference is whether they reflect it in predictable directions (specular) or unpredictable and randomized directions (lambertian). Integrating spheres are for collecting and measuring all the light entering a hole or emitted by a body (such as a lamp). Their makers strive to find the whitest paints, powders, et cetera to coat them with. I think titania and rutile and maybe barium titanate are some of their choices.