This year we decided to continue the program of experimental archaeology initiated in 2015, by producing modern replicas of EB (Kura-Araxes) and LB hearths/fireplaces discovered at Aradetis Orgora and other archaeological sites of the region (e.g. Natsargora, Kvatskhela, etc.). This activity was carried out under the joint responsibility of Marta Aquilano and Davit Darejanashvili and, after the departure of the latter, with the assistence of Modwene Poulmar'ch. This time, instead of using the firing installations in controlled conditions and with different types of fuel, we decided to focus on comparing the performances of the two different installations.
Like last year, for producing the replicas we used clay from the village of Doghlauri, next to the site, since this area is rather rich in clay. This year we decided not to sieve the clay, since last year the paste had turned out to be too fine; so we simply added water to it, leaving it to rest for three days, so that it could absorb the water; during this period, we covered the paste with a tent and uncovered it every day for one hour. After three days we added quartz (mineral tempers) and barley straw (vegetal temper) to the paste and mixed it for a long time using feet and hands, and constantly adding water.
For the experiment we created two different types of fabric: for the Kura-Araxes hearth we added more straw (about 300g on a total of 10 Kg of clay), and less quartz (about 200g) to the clay (temper 1), while for the Late Bronze hearth we added less straw (about 100g on a total of 10 kg of clay) and more quartz (about 400g) (temper 2).
The next step consisted of making the installations (hearths/fireplaces).
At first we tried to produce a hearth by simulating the fixed hearths with inner projections typical of the Kura-Araxes period in the Shida Kartli region, one example of which was also recovered this year at Aradetis Orgora. Considering the bad results of last year's experiment, when the hearth exploded in the firing phase, we decided to use another building technique: we prepared a sort of earth platform of compacted soil in the courtyard of the expedition house, on which we dug a cavity, into which we directly built the fireplace on site. We built it by adding a series of clay smoothed layers, and it took us one day to complete it (Fig. 29).
On the same soil platform, next to the Kura Araxes replica, we also tried to replicate a Late Bronze fireplace. First we constructed the base of the fireplace, made of large pebbles, by using pebbles from the Aradetis Orgora mound. Over the large pebbles we laid a thin plastered smoothed clay layer. On this thin clay layer we fixed a first layer of pottery sherds and over them we laid another smoothed layer of clay, to be used as a firing surface. We left a little hole on the firing surface, in order to be able to measure the temperature of the underlying pebbles. Finally we built the slightly raised fireplace's walls all around it.
The building phase of the two artefacts was long and difficult because the clay from this area is already mineralised by natural minerals (this is the reason why its colour is whitish); for this reason the clay gets dry sooner compared to other varieties of clay. Thus, when the fireplaces were ready, we had to maintain them humid in order to avoid the cracking of the surface, that happened very often and very fast, as they were exposed to wind and sun, even if they were protected by a tent.
After a few days, we lit a fire inside the Kura-Araxes replica, in order to make its surface hard, since it was already a little cracked (Fig. 29). For this first fire we used straw, small and medium wood sticks and pinecones. The temperature quickly reached 480 degrees, but we made an effort to reduce it (down to 300 degrees) since we wanted to fire the installation's surface in a gradual way. We had to fuel the fire very often with sticks because the temperature went down very quickly. The highest temperature of the day was reached at 550 degrees. We left the fire extinguish gradually and after 45 minutes there were only embers left, at a temperature of 250 degrees. After an hour the temperature was about 120 degrees. The day after (at 6 o’clock, after 10 hours), the surface was still warm, and had a temperature of about 80 degrees.
We observed that although the surface was already slightly cracked, the fire did not cause further damage to it. The following day we tried to make an experiment, in order to see how long it took for a pot full of water set on the hearth to reach the boiling temperature (Fig. 30). So we burned a fire at a constant temperature of 450 degrees, and we set a handcrafted clay pot bought in a bazaar on the lobes of the fireplace. We observed that the water started to boil only after 20 minutes.
After a few days of interruption of the experiment because of rainy weather, we started to use the LB fireplace replica by lighting on it a fire, that reached very quick the temperature of 700 degrees. It was difficult to maintain the temperature stable and we needed to fuel the fire very often. Even in this case, although the surface of the installation was already cracked, the fire did not cause any further damage to it.
After the surface had been hardened, we started to make the last experiment, i.e. to compare the performances of the two firing installations (Fig. 30). We therefore burnt up a fire, and reached a temperature of about 700 degrees in both hearths. After embers were created, we started to measures their temperature every 30 minutes (only on the combustion surfaces in the Kura-Araxes hearth; on both the combustion surface and the pebbles in the LB installation).
The observed temperatures are the followings:
18.00h: KA 483 LB 483 (pebbles 150)
18.30h: KA 320 LB 270 (pebbles 120)
19.00h: KA 200 LB 136 (pebbles 65)
19.30h: KA 170 LB 110 (pebbles 45)
20.00h: KA 134 LB 83 (pebbles 35)
After 20.00 we fueled the fire again and we left it create other embers to in order to measure their temperatures again and to see how the two fireplaces cooled down during the night and how they would behave during the next morning. The observed temperatures are the followings: 22.00h: KA 685 LB 595 (pebbles 245)
23.30: KA 410 LB 333 (pebbles 144)
5.30h: KA 82 LB 71 (pebbles 57)
7.00h: KA 69 LB 63 (pebbles 48)
8.00h: KA 58 LB 54 (pebbles 46)
9.25h: KA 56 LB 188 (pebbles 67) – but there was sun on this fireplace, so the measurement in not reliable.
What we can observe after this measurement is that over a short period of time the KA fireplace seems to maintain the heat better compared to the LB fireplace. This could happen because in the KA fireplace the fire is protected by the three projections, and because the installation is dug into the soil. Over a longer period of time, however, the difference in temperature becomes negligible. We can thus conclude that, over a longer period, the LB fireplace maintains the heat better. The presence of the pebbles and pottery layers probably plays a role in this situation, which we intend to better elucidate in the future.
At the end of the experiment, we covered the installations with soil, sine we hope to be able to examine their preservation after one year on the occasion of the next field season.