Young's Demonstrative Translation of Scientific Secrets / Or, A Collection of Above 500 Useful Receipts on a Variety of Subjects

by Daniel Young

190. TO PREPARE A FINE TORTOISE-SHELL JAPAN

Take 1 gallon of good linseed oil, and 1/2 lb. of umber; boil them together till the oil becomes very brown and thick, then strain it through a coarse cloth, and set it again to boil; in which state it must be continued till it acquires a consistence resembling that of pitch; it will then be fit for use.