When your Crucibles is thus prepared with the proof, then set it in a little Oven, prepared for the proof of the Copper Oars, put fire in it, and when the Cruci∣ble [Section. 2] is glowing, blow very hard with a hand-Bellows, that the proof may have a strong heat, so that it need not stand long: then take out the Crucible, and let it be cold, then beat it asunder, and you will find below a grain of Lead, so much as the 2 centner-proof-weights will yield; then draw up the Proof-weights, and you will see how many centners of the bright or deft-lead Oar will yield a centner of lead.
But to this proof must be added filed Iron, that the [Section. 3] Antimony which is in the raw lead-Oar may touch the Iron rather than the lead, for if it had no Iron to con∣sume, it would begin on the weak Lead, therefore in many places, in the great fire, old Iron, or Iron scales, slacks and sinders are to be added to the melting, whereby more Lead is produced: it hath also this service in mel∣ting, that some Lead yields foul and unclean vvork, which by the Addition of the Iron becomes clean, for the An∣timony or remaining Sulphur vvill give it self (in the melting in the Lead-Kilns) to the Iron, and will come away that so the lead may be pure.
But some Assayers pretend to set the Grain-lead [Section. 4] upon a Test, which in proving is found below in the cru∣cible, and let it drive, so it vvill become clean: which is false, for the Lead being a vveak-volatile Metal, easily consumes it self in the fire: therefore I judge that vvhen the proof hath once suffered the fire, the Lead vvill become good and clean, unless the grain of the Proof be not clean, and that there doth hang on the same Lead, ravv glimmer or stone, which is a sign that the Proof hath not received its due heat, which ought to be observ'd by the Assayer) and then he must make the proof once more.