Manufacturer and Builder 6, 1893
What materials are employed by the manufacturers of lead pencils to grade the hardness of the leads?
— C. D. A., Troy, N. Y.
Answer. It is commonly supposed that the different grades of hardness given to the ordinary lead pencils are produced by mixing the soft graphite, which gives the marking quality to the pencil, with varying quantities of clay, the softer grades being mixed with comparatively little, and the harder grades comparatively more, of the clay.
Ei kommentteja :
Lähetä kommentti