To descale a kettle, a coffee machine, or a pipe is to take off the hard white crust that builds up when you boil water again and again. That crust is called scale, or limescale — minerals left behind, not dirt. In Britain you see descale on product labels and in bathroom cupboards; people use a bottle of descaler, or vinegar. American speakers may say remove mineral deposits or decalcify instead. This entry is that household sense. Though actually, the same spelling can mean taking the scales off a fish — a different job that just happens to look identical on the page.