Does a black surface absorb all light? Graphite is intensely black. A cleaved graphite surface is shiny (about 8% light reflected). True black black demands correctly dimensioned porosity in which light gets lost, as in black velvet or hollow glass microballoons dispersed in light absorptive paint. (Solid glass microspheres create 3M reflective tape.) Black black obtains by spray painting a mesoporous white reflectance standard with cheap flat black from a hardware store. True black black loses light in crevices - blackbody cavities - and crevice color makes little difference (size counts) if they are electrically conductive (as opposed to dielectrics). Bright shiny metal is a fine route to black so black it sucks out your eyes. It is sold commercially.
Credit past employee Steve Nanchy in the R&D area of Schick/Wilkinson Sword Shaving Products Group (Warner-Lambert Company) with this tidbit:
"We sell lots of stacks of cleaned, uncoated single edge razor blades for beam dumps. 375 blades x .004" = 1.5" square target. (Do not touch the sharp faces or you blunt edges and get silver lines.)"
A razor blade's working edge is a honed brittle ceramic or intermetallic shard narrower than a wavelength of visible light. (Metal foil that thin is soft.) Light hits the razor edge and diffracts around it, plunging into vast numbers of reflections between converging metal walls. Each bounce loses a little intensity to optical absorption. Resonance conditions (quarter wavelength gap intervals, nodes at the conductive walls) create more intensity holes as the converging metallic tunnel becomes an etalon for successive wavelengths. The result of stacking tiny mirror-shiny sharpened ever-so-thin electrically conductive plates is an irreversible sump for light profoundly black black as only physics can make it.
The downside is that the easily rusted metal cannot be cleaned lest the almost atomic fineness of its edges be blunted. If you are selling rather than buying your derived pain is tolerable. Do optics labs using these things have a medicine cabinet with a little slot at its lower rear, ten stories deep, for safe disposal?
Scan the black "surface" with a monochromatic light (laser) beam, sweeping frequency, walking into and out of constructive and destructive interference. Vary blade orientation versus polarization direction. Is the stack a reflectance bandpass filter or something more curious? Magnetize it - microscopic radii of curvature occasion hellacious field gradient and divergence. What will the Faraday effect affect? Go too deep into the infrared and the surface looks solid and reflective, but with electrical and magnetic anisotropies. It could be great Science Fair fun if somebody covers the research budget.
To what dastardly missions can this knowledge of bulk razor blade ecstasy be assigned?
The optical engineering philosophy is immediately applicable to automobile radiator grills for both microwave and laser traffic citation radar. Heck, redesign the whole car with an eye toward stealth technology! Computer resources needed for continuous curvature computation of a stealth automobile are not overmuch burdensome. Every corrupt police department that squawked (every police department) would be complimentary sales publicity. The revenue possibilities are endless, as are the hushed payoffs to prevent the stealth auto from ever happening. The first person to file a patent dies quietly wealthy (or quietly quickly).
King Gillete's fortune was based upon a simple observation, namely "forget the razor, sell the blades!" The eldritch phenomenon of stacked razor-sharp shiny metal summing to ultimate blackness is perfect for incorporation into high school science curricula. Suitable Federal lobbying tempered with threats of indiscretion disclosure will have every high school kid buying a pack or three of single-edged razor blades to constructively contribute to the outcome-evaluated American zero-goal education process. The US economy will blossom, steel foundries will revitalize, mercantile trade will boom, The National Razor Blade Crisis will have new medicine cabinets emergency examined and retrofit with razor blade slots at ruinous cost to the citizenry. We will all seize Eden courtesy of a five minute physics demonstration. Isn't that what (political) science is all about?
The dark side is the bright side. Blackbodies are not only the best possible absorbers, they are the best possible emitters (First Law of Thermodynamics). Place the bolted 375-blade stack in a vacuum bell and raise the temperature. Passing 500 C there is perceptible visible emission in the deep red, intensifying and blue-shifting as the temperature rises further. Will emitted light be polarized in deference to the structure of the parallel incised emitting surface? Inquiring minds want to know!
Isn't it time your child had fun and a consequential learning experience with razor blades?