For a general introduction to the three hot extraction methods for processing mercury from cinnabar, see the section on Hot Extraction of Mercury: Sources
When it is extracted, under the blows of iron tools it sheds copious tears of quicksilver, which is immediately gathered by the miners. When these clods of ore have been collected, because of their saturation with moisture they are cast into a kiln at the foundry in order to dry them out, and the smoke that is driven out of them by the heat of the fire, once it settles again along the floor of the kiln, will be found to consist of quicksilver. Once the clods have been removed, the droplets that have settled out cannot be gathered because they are so small, but they are swept into a tub of water and there they merge with one another and are finally poured together into a single mass.
Cum id foditur, ex plagis ferramentorum crebras emittit lacrimas argenti vivi, quae a fossoribus statim colliguntur. hae glaebae, cum collectae sunt, in officina propter umoris plenitatem coiciuntur in fornacem, ut interarescant, et is qui ex his ab ignis vapore fumus suscitatur, cum resedit in solum furni, invenitur esse argentum vivum. exemptis glaebis guttae eae, quae residebunt, propter brevitates non possunt colligi, sed in vas aquae converruntur et ibi inter se congruunt et una confunduntur.
The hot extraction procedure, which primarily entails the roasting of mercury ores, became standard after the publication of Agricola’s De Re Metallica (1556) onward, whereas classical sources are less precise about the process. The Roman architect Vitruvius (1st century BCE) only records an extemporary observation, noting that to produce the pigment, the ancients used to dry moist clods of cinnabar in ovens. When the fumes condensed, mercury could be found at the bottom of the oven and on the clods. Mercury is thus produced either by reaction of cinnabar with oxygen or by distillation (HgS + O2 → SO2 + Hg). We tried out the procedure and verified the reaction using modern laboratory equipment.
In order to replicate more closely the work of ancient alchemists, we tested this by heating the cinnabar ores within an alumina crucible that was covered with a lid (Figures 1-2). In a crucible, the cinnabar sublimes and partially reacts with atmospheric oxygen, yielding mercury that condenses on the lid. The amount of oxygen estimated to be inside the crucible is insufficient to complete the reaction. Indeed, residual cinnabar and black metacinnabar (polymorphically stable at high temperatures) were always observed, even after prolonged heating (Figures 3-4).