The discovery of a 13th century tar works or settlement

Tar-making belonged to the so-called forest crafts, along with coal mining, ash making, tar-making or even glassmaking. Their remains can be found here and there in the form of pottery fragments, pans or glass drops in forest streams or in clay scattered by animals. Or, as in this case, quite by chance when digging up another find.

History and use of tar and pitch

Tar and tar products have been known to mankind since prehistoric times. The earliest evidence of the use of tar comes from the Dutch beach of Zandmotor, where a siliceous tip coated with birch tar, some 50 000 years old, was found during construction work. Tar was commonly used in prehistoric times, for example, to attach microlithic tools to wooden and bone handles or to glue ceramic vessels. Resin lumps are also occasionally encountered inside urn graves or loose in settlements, but their interpretation is difficult. The purposeful production of tar in special facilities is only encountered in Roman times, and even in central Europe in the early Middle Ages. In Bohemia, the earliest evidence of tar pits dates from the 11th to 12th centuries. Traditional forest tar production was maintained until the beginning of its industrial production in the mid-19th century. In the Middle Ages and the modern period, tar was used to impregnate barrels, ropes and fishing nets and to coat shingle roofs. It was also used to treat skin diseases, for hoof pains and as a combustible for torches. Mixing tar and grease produced colomass, used to lubricate wagon wheels or wooden gears in mills, hammers and ironworks.

Production technology

Resinous conifers such as pine were most suitable for tar production, spruce and larch less so. The selection of suitable trees is described, for example, by J.L. Hartyg, in his book "The Art of Forestry" from 1849: "If a good, blackened, liquid and oily colomaz is to be obtained, it is well to pay particular attention to the selection ofAll coniferous wood will yield colomaz. But not every coniferous species and piece is so abundant in colomaz that we can profitably extract it from it. Pine trees are particularly useful for burning colomaz. The roots and stumps of old pines, felled some years ago, and such as by any chance contain so much resinous and oily sap has accumulated so much that we can tell by its yellow-brown colour, its strong smell, the unusual weight of the wood and the black surface of the trunk."

The oldest development was the production in the so-called tar pits, which are found in Central Europe from the 8th to the 12th century. These were funnel-shaped pits 1 metre in diameter, consisting of a decomposing part where the pitched wood was airtightly sealed, above whichand a sink below, where all the liquid products of this dry distillation were collected.

Not long afterwards, the production of tar in myrrh was introduced. These charcoal kilns were similar to the classic charcoal kilns used for the production of charcoalbut, unlike them, they were fitted with a spout in the bottom which allowed the tar to be collected. This method of production was often used until the end of the 20th century.

From the 14th century onwards, the most advanced production technology was the double chamber kiln, which was used without significant changes until the 19th century.century. They consisted of a firebox and a decomposition chamber and were usually located on gentle slopes, close to a water source. A bowl-shaped depression was formed in the slope, lined with flat stones, above which two domed chambers were built. The inner decomposition chamber, built of mud or bricks, contained resinous wood, while the outer chamber, called the "chamber of the chamber", was made of mud. The outer chamber, the ambient chamber, was filled with firewood, which was replenished during the process through holes in the shell-jaw. All liquid products then drained through a channel in the bottom of the kiln into the containers provided.

Finding

The site was not chosen at random. It is located near a place name where a gamekeeper was supposed to have found several pottery shards clogged with tar during forestry work in the 1950s. Unfortunately, their location was vaguely located to the number of the stand and the place name. With the idea of tracing the site, I set out. Soon I was standing on the edge of the aforementioned stand, tall forest alternating with young thickets, and the overall appearance was waterlogged and unpleasant. I switch on the detector and set off. Along the way, I scan every crevice and every spot raked by game, looking for odd landforms, but nothing. After a few hours, I turn back, and sort of on a hunch, I head for a place where I know from the maps that the spring forms a short but fairly deep valley here. The first signal was the cartridge, and the very second target a few meters down was the knob. And that was the discovery. Pretty much right after the scoop was turned, a ceramic shard peeked out at me, just below the rake and another below that. I extended the trench to about 50x35cm and from that area alone, to a depth of 25cm, I traced about 200 pieces of shards.

I was told by the museum that this was not a 1950s collection site, but a new site. However, there is a match here in the dating around the mid-13th century, and the black inscription on some of the sherds. However, the composition of the assemblages is different. The former contains mainly thick-walled and poorly decorated technical pottery with simple rims, while in my case it is exclusively decorated wall fragments of potsherds with engraved lines, engraved helix and ridge ripples, and only with swollen raised rims. While the black patch might indicate a defunct production, the assemblage has, thanks to the numerousornamentation and the absence of typical technical pottery, it has a residential character, and is unusually large for a dehter's site. Only analysis will confirm whether it is tar or burnt e.g. from cooking food. In April, we are going to visit the site with an archaeologist, take a closer look at the site andsurrounding area, possibly looking at interesting landforms and other finds.

Resources
http://archeologiatechnica.cz/sites/default/files/2018-04/83-%2090%20Woitsch.pdf
https://dspace.cuni.cz/bitstream/handle/20.500.11956/20907/DPTX_2008_2_11210_ASZK10001_127630_0_72184.pdf?sequence=1
https://theses.cz/id/vzidrx/22421504

The oldest method of tar production in a pit

Tar production in the mill

One example of a double chamber kiln

A two-chamber kiln depicted in a 1676 town charter

Black lime

Swollen and drawn edge types

Fragment of rim decorated with horizontal engraved lines

Large undecorated pieces of pottery

Most commonly represented decoration with horizontal engraved lines