A sander is a power tool used to smooth surfaces by abrasion with sandpaper. Other tools can include chisels, pliers and more with sandpaper or pumice stone for smoothing. Zirconia is a component in some abrasives, such as grinding wheels and sandpaper. Participants wore pajamas decorated with sponge, sandpaper, and aluminum, and ate salads without using cutlery. They start with sandpaper and finish with stain. Their skin is covered in placoid scales "(dermal denticles)" that are as rough as sandpaper. These bumps are what give the characteristic sandpaper texture to the rash. The brown skin has a texture somewhat between sandpaper and the fuzz on a peach. The blade is taken through a series of increasingly finer grades of sandpaper. The small rocks entrained by plucking act like sandpaper to the downhill slope. Many types of sandpaper use aluminium oxide crystals. World Championship of Ping Pong uses old-fashioned wooden paddles covered with sandpaper. Sandpaper and wood finishing tools were generally unavailable to the Hopi in this era. This helps prevent clogging of the sandpaper. These might involve dying, pressing, and even using sandpaper and drills on the raw jeans.