Antique texts for the extraction of wood tar

by Albrecht Locher
Translated from German by Susan Verberg, 2019

Published in ACTA PRAEHISTORICA ET ARCHAEOLOGICA - 23
Das 1. Symposion zum Thema „Holzteer“ vom 16.-17.6.1990 im Museumsdorf Düppel, Berlin
(“The first symposium on the topic "Wood Tar" from 16.-17.6.1990 in the museum village Düppel, Berlin), edited by Andreas Kurzweil und Dieter Todtenhaupt

Summary [English]: Archaeological authentic proves of wood tar production do not exist from Mesolithic to early medieval times. Only two, perhaps three remarks about the manner of obtaining tar are to be found among the written sources, in spite of the fact that it is possible to quote numerous literary hints about the use of tar in techniques and medicines. Theophrast (371 — 287 BC), successor of Aristotle at the school of Athens, describes in Hist. Plant. 3,9,1 -3 a charcoal burner, constructed in such a manner that the ground floor was tightened and shaped as a funnel that runs into a waste-pipe. Pliny (23/24-79 AD) describes contrarily an oven in which small pieces of chopped woods are heated by a fire that is burned from the outer side; that installation might possibly be one whose principle of construction is similar to finds of the Middle Ages. The third remark, rather problematic, is to be found at Theophrast (Hist. Plant. 5,9,4 together with Pliny. Hist. nat. 16.23), who describes the deriving of oak charcoal, yet giving a hint, that the charcoal burner was round around ..greased up“. Pliny repeats this correctly. but adds that the workers make hollows into the charcoal burner to let drop out the „sweat“, i.e. the liquid, which is tar wood. Since the connection of the literary sources is difficult to explain (direct use of Theophrast with arbitrary Interpretation or a different source?), this quotation only can be used as source in a very restricted manner. The round around „greased“ charcoal burner could have been an intermediate phase of technical development between the modified one Pliny describes, and the oven constructed of loam, respectively enwalled. It remains an open question whether Pliny gained his knowledge of the distillation procedure by means of an early alchemistic source, he is said to have used.

There is a remarkable gap in the archaeological finds for the reconstruction of the technique with which wood tar has been won. Between the Mesolithic and early Middle Ages, a gap of roughly 5000 years has to be exclusively bridged with texts.

Assuming that the archaeological finds and the descriptive texts complement each other - at least in principle, whereby the weighting of the individual page can vary - the case is complicated by the fact that the process must be obtained exclusively from words. Great care is needed. For if one tends to put known texts too quickly in relation to near-tangible finds, they can succumb to a kind of Schliemann temptation. The otherwise so reliable Blümner (1879, 353), for example, quickly turns a simple tub (alveus) into an oven!

There are numerous written testimonies in literature and inscriptions for the use of wood tar in medicine, veterinary medicine and technology. However, news about the technique of extraction are very sparse; there are two, perhaps three. The first of these texts was written by Theophrast (371-287 BC), pupil of Aristotle and the successor after him in the direction of the Peripatetic school. He clearly practiced typical Aristotelian "looking down" - and therein lies its significance for the history of philosophy as well as of the individual sciences. After faithfully succeeding his teacher, he switched philosophical speculation for the systematic collection of individual observations and empirically determined facts. ln his study of plants (Historia plantarum), he explicitly touches the extraction of wood in Book IX (plant juices and resins) and in the margin in Book V (Wood and Woodworking).

(The translation is based on the most accessible text of Theophrastus: Theophrastus, Inquiry into Plants, ed. A. Hort London 1948-49 [LCL].) It [the translation] takes no aesthetic considerations and above all, does not attempt in case of doubt to described in an explanatory way any technology even in the least meaningful places.) Theophrastus, Hist. Plant 9,3,1-3:

 "They burn the tar in this way: After they have prepared a steife [?], as if they made a (round) threshing floor, which confluences [bowls] to the center, and then tamped down well, they split the fatwood
5 stumps and stack them together in a similar arrangement as in the kiln of the coal burners, except that it does not have a depression. The split pieces, however, place them side by side so that the height increases with the quantity. They say that if the kiln
10 has a circumference of 180 cubits, the height would be at most 60 or 50 cubits, or if both dimensions were ever to reach 100 cubits; importantly, the fatwood is rich in resin. Now, when they have set up the kiln and covered it with xxx, they cover it completely with dry earth, so that the fire never
15 breaks through; the tar spoils, if the two unite. They ignite from below through the (still) free passage; then they also block this opening with xxx and pour them. They watch (the kiln) ascending a ladder, see if they see smoke
20 rising, and then they keep throwing earth on it, so that nothing flares up. But there is a channel furnished for runoff of the pitch through the kiln into a pit, which is about 15 yards away. The outflowing pitch is cooled to the touch. Burning is for a maximum of two days and nights; on
25 the following day, before dawn, the combustion process enters the stage of completion and diminishes. Because that happens when the kiln no longer flows. All this time they are watching, without sleeping, so that nothing flares up, and they sacrifice, and they pray under festive
30 rituals that the tar may be abundant and beautiful. That's how people burn in Macedonian lands. "

1. Several recipes in Hippocrates, Dioscurides and Galen contain xxx, in Hippocrates several times xxx xxx so probably pitch-wax ointment. Greek inscriptions and Latin literary testimonies (Vitruvius, Pliny) testify to xxx pix as a preservative or sealant. The complete list of mentions [is not reproduced] since it does not serve any purpose, nor does it contribute to the question referred here; it can be requested from the Philological Seminar of the University of Tübingen if necessary.

The text is so vivid and precise that explanatory notes can be limited to the most necessary: ​​for instance, 1. Tar: The context makes it unmistakably clear that we are talking about wood tar. Otherwise, however, the ancient terminology is full of blurring. Here the minerals bitumen and asphalt are given the same names as the organic resins, in the latter case [even] all the stages and methods of extraction and processing are indiscriminately designated by the same words, with consequences to this day: Retsina is still a resinated wine; in the Romans, the word for resin (crapula) even served as a term for the intoxication caused therewith. For details, see André (1964, 96 f.); Büll (1955, 801) and Forbes (1955, 4 f.). Z. 3: Confluence stands for the Greek crupporj. This is reproduced as literally as possible; what is meant is not a gutter which one would think of, but only a funnel-shaped decent inward, which causes the confluence [bowling] to the center.

Z. 10-12: The given numbers are difficult. If the circumference of the kiln is approximately correct, then the height, even if one chooses the smallest possible yard of about 45 cm, results in gigantic dimensions. A height of more than 20 m could not have been scaled with ladders (Z. 19).

Z. 13 u. 18: xxx [indicates original Greek alphabet] remains untranslated. Blümner's translation of "wood" (1879, 351) is downright grotesque in terms of its technical purpose. xxx is simply "mass, material, substance.” Since this "substance" is clearly distinguished from earth (lines 14 and 20), it must have been the craftsman's term for a special covering compound ("personal communication" with A. Kurzweil). "Material" ("madral") [possibly “lute”] in a variety of common forms has to this day the same function in various craft trades. Z 23-24: Touch probably means contact with the cold floor and the walls of the pit.

If one ignores the likely incorrect dimensions, the text is technologically clear and unambiguous: it describes a coal kiln, which has received an additional device for the production of a by-product. And here, main and by-product change places.

The next text is about 400 years younger; it is in the Naturalis Historia of Elder Pliny in Book 16. In order to properly appreciate the meaningfulness of this text, necessarily one must consider some of its literary peculiarities. Pliny the Elder was born in 23/24 AD, received training in rhetoric, followed by the usual preparation for an administrative-political career. He was an official in civil and military functions under several emperors, traveled often, also as commander of the imperial fleet in Misenum. After writing in various fields, it is here he completed his Naturalis Historia, the only fully preserved encyclopedia of Roman literature. The writings of Pliny, which after centuries of almost canonical validity has become unduly undervalued since the last century, will be adequately appreciated here, even considering that Pliny was not an expert in almost any of the fields he covered. In addition, we are very well informed about his way of working: his nephew and adoptive son, Pliny the Younger, a kind of ambitious salon writer, has left a detailed letter (3, 5) in which he accurately portrays his way of working. Pliny the Elder worked all day and night, reading and dictating, which he did not give up even while having to be carried in a litter, being in the bath, and finally even when in mortal danger, and thus ended up with 160 books of notes. It speaks very much [to his credit] that these notebooks were already arranged according to a specific keyword system. But in the reordering of the individual information according to the keyword system, of course, coherent texts were partially broken down into smaller individual parts. Thus, in the Naturalis Historia there are references, of which one can come from a completely different source than another. Now imagine this re-editing, carried out by a man who could exercise none or hardly any objective criticism of what he wrote down. Therefore, Pliny often passes on information in a "blind" way. It has only recently become clear that this does not diminish the value of his information, but occasionally even enhances it, as long as is kept in mind which alterations and translation errors one could expect.

Now for the text:
Pliny, Nat. 16, 52-53 translated to the edition Jan / Mayhoff, Leipzig 1892-1906

"Liquid pitch is cooked in Europe from the pine; it is used for the preservation of ship parts and for many other purposes. Their wood is beaten and heated in kilns surrounded on all sides by fire.
5 The first liquid flows like water in a channel (down). This is called "cedrium" in Syria; it has such an effect that corpses doused with it are preserved in Egypt. The then already thicker liquid gives the tar. This is in turn thrown into bronze cauldrons
10 and thickened with the help of vinegar which acts as a thickening agent. It has been given the nickname "strong pitch" and is used favorably for barrels and other containers; it distinguishes itself in the stickiness from the other tar, also by its reddish color and by the fact that it is heavier
15 than anything else. It is made of spruce resin, which is thickened in stacks of solid oak wood with glowing stones, or, if you do not have such vats, (it is produced) by creating a pile / stack, as is common in the charcoal burning. "

The text is commented in detail by André (1962, 117). This is one of Pliny's typical groupings of individual texts from very different sources (Andre: "Gauchement juxtaposés"). Clearly, however, is the crucial point in our context, lines 3-4. It is clearly an oven that is heated from the outside. That Plinius uses a different word here for oven / furnace (furnus) than for metal furnaces (fomax) may not necessarily mean anything. It may be due to the source. Another negative factor for the technical value of infiltration is the fact that the process inside the stove is described with a rather poetic-rhetorical word (fervet - boils, glows). The casualness with which the furnace itself is spoken off makes it very probable that Pliny did not see such an installation himself. Nevertheless, what he so casually mentions is a decidedly different procedure from that described by Theophrast. It is, in principle, a forerunner of one of the variants of the process, for which archaeological evidence has been available since the Middle Ages. Pliny's explanation of the technical process also speaks of the combination that he makes in lines 17-19: he first correctly describes that liquid pitch is thickened with glowing stones. What follows, then, is not a technical alternative to gaining firmer pitch, but simply another method, namely that described by Theophrast. Pliny is here on the threshold of another serious blunder, which is only hinted at: probably misguided by the ambiguity of the word for resin (resina), Pliny mixes processing methods of cold-won tree resin, such as for winemaking, with those won by dry distillation; this is clear from the next, not reprinted text §§ 54-58.

Closely related to the working method of Pliny is another problematic point, which is at least indirectly connected with wood tar. In here is something else can be found: the first of the 37 Naturalis Historia books is just a comprehensive list of the following 36 books. In it, the processed information is not only scrupulously classified (and also counted), but it is also listed for each [entry], from whom the information is related or excerpted. Among the non-Roman authors is in third place Theophrastus. Therefore, it is certain that Pliny had theophrastic writings available, but we do not know which ones in particular. It is obvious that the detailed passage from Theophrast Hist. Plant, as translated above, does not appear in Pliny, n. 16, 52 ff. In another text, however, which deals with coal burning and (at least with Theophrast) not with the production of wood, it is clear one influenced the other.

Theophrastian Hist Plant 5,9,4 (edition A. Hort, London / Cambridge / Massachusetts 1948; LCL)

1 "They saw (the wood) and select the minerals
2 and smooth pieces for coal production. It is necessary to assemble them as tightly as possible
3 in order to achieve reduction of the air supply. When
4 they then smeared [covered] the kiln, ignited it and poked it
5 with skewers at certain intervals. This kind of wood
6 they also look for for coal mining."

Compared to: Pliny, Nat 16,23 (edition Jan / Mayhoff, Leipzig 1892-1906)

1 "The heaps of erected fresh logs are fired with clay
2 into a furnace-like structure formed by the kiln
3, so the hardening shell is pierced with skewers
4 to allow the liquid to escape"

The connection between both texts is confusing. This begins with Theophrastus in line 4: With "smeared” the Greek xxx is reproduced here. This seems to indicate a different design of the kiln than in Hist Plant above. 9, 3, 2 (see here p. 112), at least as long as neither the xxx nor the "earth" ability to smear / spread is attributed. The poking may have allowed the required minimum of air supply. The question here is if Pliny had this text in mind; whether it was this text alone or also the one next to it, is burdened with philological problems. Doubtless Plinius returns to the "smear" in the "clay" (luto, or lute) again (line 1), However, what is said in the words "formed into a furnace-like structure" raises further questions. Pliny here is simply "luto caminatur" - "becomes with clay ..." and now follows a verb only Plinius has demonstrably used, and twice, as the only Latin author of the ancient world. Incidentally, in the second place (Hist. Nat. 17,80) it marks the shape of a planting hole for a tree. The complicated sparse lexicographical material makes it possible to use the following alternatives as a solution: if Pliny has the (folk) Latin word from a Roman source or verbal communication before him, then it can mean almost everything that goes with it, including the form, function or purpose of a stove is in any context (the medieval "caminare" means "equipped with a fireplace"). The second possibility is this: Pliny often takes over Greek words by simply transcribing them in Latin; and the verb xxx exists in Greek since Theophrastus. It is said that he smelt (not in the texts translated from Hist. Plant., but in De lapidibus 69), as well as in the pseudo-Aristotelian writing De mirabilibus auscultationibus 833b23, where it means iron smelting. Pliny then continues (line 3-4): under the influence of the heat, the "shell" consisting of "clay" hardens ". Here is "calixder" mug ", the word that has entered as the" helmet "in the Latin of the alchemists. This hard "shell" is now punctured to let "the liquid" escape. That's not the case with Theophrast. What is certain, however, is what this liquid is about: wood tar. But it is completely unclear whether Pliny here simply interprets the theophrastics arbitrarily or whether he alludes to information from another source. This could have been Varro, the great diverse historian of the outgoing Republic; he is often the main source of information for Pliny and is in the author's directory of book 16 in first place among Roman authors.

Result
In all interpretation difficulties and uncertainties, especially in Pliny, there is no doubt that:

1. Between 350 BC and 100 AD two techniques of wood extraction were known in the western Mediterranean. One described by Theophrastus uses a modified charcoal kiln specifically designed to trap the liquid.

2. Pliny knows a decidedly different method: An oven is used in which the heat is generated by a fire built around it. This principle may have been a precursor to the medieval and later smelt oven.

3. The two last composed texts from Theophrastus and Pliny - if one assumes certain deviations in the transfer of information [i.e. transcripts and translations] - where the extraction of wood in the modified charcoal kiln by changing the outer skin of the kiln, the way to the solid from the outset [?], made of struck clay or brick oven. But it might be just as plausible that both techniques may have existed independently and side by side.

Outlook
Lastly, there is an open question that is still awaits answering: the distillation process, which is used in wood extraction, played a decisive role in alchemy. Pliny does mention a "Democritus" with all relevant books in the author's directory. Under this name, writings were written in antiquity that have nothing to do with the great philosopher from Abdera, but represent the oldest surviving alchemical literature. It is difficult say for sure and I have been so far unsuccessful to prove that Pliny was dependent on this literature for even one convincing single citation3. Your author hopes to be able to help solve this problem in the foreseeable future.

Bibliography
André 1962
J. Andre, Pline TAncien, Histoire Naturelle, Livre XVI, Texte établi, traduit et commenté par J. Andre. Les belles lettres (Paris 1962).
Andre 1964
J. Andre, La résine et la poix dans lÄntiquité, technique et terminologie. LAntiquité Classique 33, 1964, 86-97.
Blümner 1879
H. Blümner, Technologie und Terminologie der Gewerbe und Künste bei Griechen und Römern. 2. Band (Leipzig 1879).
Büll 1977
R. Büll, Das große Buch vom Wachs (1977).
Forbes 1955
R. Forbes, Studies in Ancient Technology I (Leiden 1955).
Fuchs 1985
R. Fuchs, Art. Teer, in: Lexikon der Ägyptologie V (Wiesbaden 1985) Sp. 289-293.
Marcille 1941a
R. Marcille, La poix antique. Revue tunisienne 1941,215-219.
Marcille 1941b
R. Marcille, La résine et la poix dans Pline. Revue tunisienne 1941, 220-228 (dem Verf. wie auch Marcille 1941a nicht zugänglich).
Projektgruppe Plinius 1989
Plinius der Ältere über Blei und Zinn. Werkheft 10 (Tübingen 1989).
Schramm 1937
A. Schramm, Art. Pech, in: RE 37. Halbband (1937) Sp. 1-5.