Metal confetti
Not very long ago, I mounted some metal fixtures, made of 304 stainless steel. The fixtures were intended to be affixed to their substrate using adhesive and each one came with a tube of glue. How robust an attachment the stuff would create, I cannot venture to guess, and I opted to use screws.
At the places on the fixture where I needed to make holes for fasteners, the material was thin enough that I could do it using a sheet metal punch (with an M4 punch and die installed) rather than drilling. There are various types of manual hole punches. The one I employed is very similar to the tool shown in this how-to video:
The matched pairs of punches and dies included with this tool possess round cross sections and, in each matched pair, the outer diameter of the solid punch is a teensy bit smaller than the inner diameter of the hollow die. Every successful use of the tool produces a small, where the punch presses the target material against the die until it shears at the lip of the die, produces a circular metal confetto. They’re slightly bowl-shaped because the force exerted through the punch on the metal sheet deforms the metal before it breaks.
Three of the eight confetti shown in the image above, the ones with a slightly duller finish are facing convex side up (or die side up) The rest are concave side up (or punch side up). The glossy-versus-satiny finish difference was present in the material to begin with, perhaps a consequence of the rolling process (as with aluminum foil: ElI5: Aluminum foil one side shiny other side dull), and wasn’t caused by the punching process.
Each confetto also features a central dimple or pock (if the metal blank is sitting concave or convex, respectively). This mark corresponds to a protuberance at the center of the otherwise flat face of the punch. The black markings are Sharpie marker pigment.