Hot extraction of mercury: Sources

Ancient alchemical texts exhibit a strong fascination with mercury due to its mechanochemical properties, which captivated early practitioners. The AlchemEast project conducted a thorough investigation into the specific procedures followed by ancient alchemists to extract mercury from cinnabar. Based on the treatment of this mineral—either through grinding or heating—we can classify these procedures into two distinct groups: “cold extraction” and “hot extraction”. The following section delves into the primary sources for the “hot extraction” methods.

According to ancient sources, the hot extraction method for processing mercury from cinnabar can be divided into three procedures: 1) simple heating of cinnabar; 2) heating cinnabar in a closed vessel in the presence of iron; 3) heating cinnabar in the presence of a substance known as ‘natron oil’ in a closed vessel.

1. Simple heating of cinnabar
The hot extraction procedure, primarily involving the roasting of mercury ores, became standard after the publication of Agricola’s De Re Metallica (1556) onwards. Classical sources are less precise about the process. An extemporary observation was recorded by the Roman architect Vitruvius (first century BCE). He noted (On Architecture, VII.8.1-4) that the ancients used to dry moist clods of cinnabar (Figure 1) in ovens to produce the pigment.

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. [see the replication]

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.

Native mercury droplets (Hg) from cinnabar (HgS)
Native mercury droplets (Hg) from cinnabar (HgS)

2. Heating cinnabar in a closed vessel in the presence of iron
Since the first century BCE, recipes for hot extraction techniques have specified the use of closed vessels. These vessels served two purposes: facilitating the recovery of mercury and protecting ancient alchemists from its fumes, whose toxicity was already well-known in antiquity . In their attempts to extract mercury, ancient alchemists experimented with adding other ingredients to cinnabar before roasting it in closed vessels. The importance of iron in this process is confirmed by both Dioscorides (De materia medica, 5.95) and Pliny the Elder (Natural History, 33.123).

It (i.e., cinnabar) is put in an iron shell in flat earthenware pans, ad covered with a convex lid smeared on with clay, and then a fire is lit under the pans and kept constantly burning by means of bellows, and so the surface moisture (with the colour of silver and fluidity of water) which forms on the lid is wiped off it. This moisture is also easily divided into drops and rains down freely with slippery fluidity. [see the replication]

(minium) patinis fictilibus impositum ferrea concha, calice coopertum, argilla superinlita, dein sub patinis accenso follibus continuis igni atque ita calici sudore deterso, qui fit argenti colore et aquae liquore. Idem guttis dividi facilis et lubrico umore compluere.

Dioscorides’ entry on mercury (De materia medica, 5.95) was also included in the final section of the alchemical Leiden Papyrus

They put an iron shell containing cinnabar in an earthenware vessel and enclose it with a convex lid smeared on with clay; then they light a fire upon (the vessel) with charcoal. The vapour that settles on the lid, when wiped off, is mercury. [see the replication]

θέντες γὰρ ἐπὶ λοπάδος κεραμεᾶς κόγχον σιδηροῦν ἔχοντα κιννάβαρι, περικαθάπτουσιν ἄμβικα περιαλείψαντες πηλῷ, εἶθ’ ὑποκαίουσιν ἄνθραξιν· ἡ γὰρ προσίζουσα τῷ ἄμβικι αἰθάλη ἀποψηχθεῖσα ὑδράργυρος γίνεται.

3. Heating cinnabar in the presence of a substance known as ‘natron oil’ in a closed vessel
Besides iron, other substances were added to cinnabar prior to roasting the mineral. Reliable Byzantine sources report that the alchemist known as Pseudo-Democritus (1st century CE) ground cinnabar with ‘natron oil’ and placed the mixture in a ‘double vessel’ to capture all of the vapor, which was associated with the mercury ‘hidden’ in the ore.

Τhis very famous philosopher (i.e., Pseudo-Democritus) said: ‘Who does not know that the vapour of cinnabar is the mercury of which it is composed? Therefore, if anyone grinds cinnabar with oil of natron, mixes them together, puts them in the double vessels and lights a persistent fire, he will collect the entire vapour that was sitting in the bodies (of cinnabar).’ [see the replication]

Οὗτος οὖν ὁ ἀγαθώτατος φιλόσοφος· Τίς δὲ οὐκ οἶδεν ὅτι ἡ αἰθάλη τῆς κινναβάρεως ὑδράργυρός ἐστι, δι’ ἧς καὶ συντέθειται; Διὸ καὶ εἴ τις ἐλλείωσας αὐτὴν τὴν κιννάβαριν νιτρελαίῳ, ἀναφυράσας καὶ περικλείσας ἐν ἄγγεσιν διπλοῖς, ὑποκαύσας φωσὶν ἀλήκτοις, πᾶσαν αἰθάλην λήψεται ἐγκεκαθημένην [lege ἐγκαθημένην?] εἰς τά σώματα.

The same procedure is described in a Byzantine anonymous recipe, the dating of which is uncertain

On cinnabar. You must know that the transformation of cinnabar happens by means of the oil of natron: in this way cinnabar is melted by a light fire, as you know. [see the replication]

Περὶ κινναβάρεως. Δεῖ γινώσκειν ὅτι ἡ ἀνάκαμψις τῆς κινναβάρεως διὰ νιτρελαίου γίνεται, καὶ οὕτως χωνεύεται μετὰ πυρᾶς λεπτῆς, ὡς ἐπινοεῖς.