The best way of re-blackening the impressed figures and divisions of thermometer scales on boxwood is to use a drawing pen filled with japan black; this would of course be a rather tedious operation. Another method, but not so good, is to paint the boxwood scale all over with japan black, making sure that it enters all the lines and figures : then roll up a piece of smooth cloth into a ball, damp it with turpentine, and with this remove from the boxwood all the japan black with the exception of that in the depressions. This should not be difficult if the rubber is used gently and the impressions are deep.