A pocket
knife is used for cutting suitable materials rat her than prytng and scratching
rocks, which will spoil the blade. Scratch tests can be made with a sharp
steel needle, which may be mounted permanently as follows: (1) cut a 4-in.
(10-cm) piece from a green sapling branch as thick as a heavy cut a
needle in half with a pair of pliers; (3) holding it in the pliers, force the cut
end about I cm into the piece of sapling; and (4) add a cap eraser that will
cover the needle and fit snuggly on the sapling (Fig. 2-1B).