Rubber is extracted from the milk sap (latex) of the heveas. Extraction is done by tapping the living tree with the tapping knife. The latex is cut transversely. Therefore, the tap cut is made at an angle of approximately 30 ° to the horizontal plane, causing the latex to run off the cut. A metal gutter is attached under the cut, through which the latex ends up in the receptacle (1).
The tap knife has a metal curved blade with a U-shaped curved lip at the end and a straight wooden handle of approx. 10 cm. When tapping, a strip of bark of about 1.5 cm thickness is cut away with this sharp lip.
The tap knife resembles the timber scribe with which a tree to be felled is marked and the clog maker's timber scribe with which the clogmaker applies decorations to clogs. [MOT]
(1) See eg VAN DEN ABEELE & VANDENPUT: 374.