The answer is "well, sorta" and requires some elaboration. Light which
falls on the event horizon of a black hole will certainly not be seen
again. Is a black hole a "substance?" I'm not sure. Also, black holes
radiate light (and other particles) via a fascinating process called
Hawking radiation. One might say that light is absorbed and then
re-radiated (at different frequencies). Does this count as "absorbed?"
More practically, you can make stuff which absorbs nearly all
light which shines on it. Black paint on a flat surface doesn't do a
perfect job, reflecting maybe a few percent of the light that shines on
it. Some black surfaces are very shiny (think of polished black leather
shoes). Fortunately you can do much better than this if you really want
to absorb some light. You can make a box, painted black on the inside,
entirely closed except for a small hole in one of the faces. Light
shined in the hole will bounce will be mostly absorbed on the opposite
face, and some will bounce off. Most of the reflected light will hit
other faces of the box, and only a tiny amount will come back out the
hole. Making the hole smaller or the box bigger makes the hole
"blacker".
A variant on this approach is to paint black the inside of a cone
with a small opening angle. Light coming in along the axis of the cone
hits the side wall, and most gets absorbed. The remainder gets
reflected at a small angle, and must be reflected many times before it
changed direction to come out the other side, reducing the amount of
reflection.
A variant on the cone approach is to coat a surface with black
paint that has lots of little pits and holes in it -- each one acts
like the cone mentioned above. Some applications, like cameras and
telescopes, need surfaces painted very black to reduce the amount of
light contamination that can blur images. Here's a of such a new kind of coating.
Note: Just because an object absorbs all the light that hits it
doesn't mean that it's black. Something that's hot will glow, even if
it absorbs all the incoming light. Heat up the box or the cone above,
and they will radiate energy in the form of light. The sun is most
likely a very good absorber of light that hits it, but it would be
rather hard to tell how much gets reflected because of all of the other
light that gets emitted (although there are tricks of course which can
be used to separate a signal from all the background -- this sounds
like a good experiment!).
As for bending light: You can change the direction light goes in
with gravitational fields, but it is easier to do it with lenses and
mirrors.
Tom
(published on 10/22/2007)
