Nine Books on the Nature of Things

Know also that any flint taken from river water and placed in a cucurbit, with its own river water poured over it to fill the vessel, can be made very large alchemically in a few days—something the Archaeus of waters would scarcely do in many years. Distil the water off while any drop still rises, until the stone is dry; refill the cucurbit with that water and draw it off again. Continue until the cucurbit is full of that stone. If you then break the glass against a rock, you will have flint in the shape of the cucurbit, as though it had been poured into the glass. Although this benefits you nothing, nevertheless regard it as a marvel.