The Hunt for Tar Kilns

Out of all the archaeological remains around Satakunta region, there’s a certain type of archaeological heritage that's probably the easiest to find, but still often overlooked and rarely researched – that of course is tar kiln. While I rarely hear much enthusiasm among archaeologists towards these remains of historical tar production, their appearance and presence has always strangely fascinated me. So, it’s no surprise, that I’ve found time to visit a few during my weeks in Satakunta!

Tar kilns (‘tervahauta’) are basically dry distillation ovens, that were used to produce tar from wood. While there are a few distinct styles of tar kilns, they most commonly appear as primitive holes in the ground with sloped walls towards an outlet hole, which allowed the tar to pour straight into a container. These kilns used to be filled with wood, which was in turn covered with a tight layer of dirt and moss. Burning the kiln with a low level of oxygen caused tar and pitch to drip away from the wood into a container, which could then be transported for example to the use of shipbuilders.

Tar production was an important source of income especially from the 17^th to 19^th century and remains of tar kilns appear in a large part of the country – however research of their types, dating and distribution has been somewhat nonexistent. While only some dozens are marked into the database of the Finnish Heritage Agency, thousands have been registered by the Finnish forest administration agency Metsähallitus.

Beautiful tar kiln in Säkylä with a surprisingly well-preserved outlet hole.

Same tar kiln shown on a hillshade model.

There are quite a few ‘strategies’ to finding tar kilns and I’ve found maps to be the most useful tool for the job. While of course some tar kilns are already marked on the maps, there are also more discreet hints to spot a suitable area. The easiest is to just look for place names that include words such as "terva” (tar) or “hauta” (grave/trench) in them, as they usually hint of tar production activities from the past. Search is best to concentrate on areas that would have been suitable for tar production - that is an area with a lot of pine trees and access to a water-way for transportation.

Another way to ease the search tremendously is by using freely available hillshade data for example on Kansalaisen karttapaikka. Preserved tar kilns are usually fairly easy to spot on the model, as they often appear as doughnut-like features due to the hole in the middle and walls surrounding it. Often these procedures follow each other, as it's best to start by looking for fitting place-names and then scan the area more closely with a hillshade model. Kansalaisen karttapaikka is an useful site for this purpose also because of the other available features, such as measuring tools and coordinate pointers.

Visiting the site is the next step. At this point the details of the kiln are written down along with a description of the surroundings and possible threats to the preservation of the site. Further documentation is done by photographing and measuring the kiln and other possible constructions - also more exact coordinates are taken from the center of the kiln. If it's reasonable to believe that the kiln is more than a hundred years old, it's protected under the Antiquities Act and the information is added into the database to wait for further research.

While the topic has not yet attracted much interest among archaeologist, sooner or later someone will end up surveying this part of history as well - tar production used to be a major source of income in the past and now it has potential to be a major source of information about local economies from the time before Finnish independence.

If you're interested in the topic, check out this instructional video for building a tar kiln (in Finnish).

In case you've discovered a tar kiln that isn't recorded into the archaeological database, follow these introductions to report it to the Finnish Heritage Agency.