Stone slab furnaces in the Finnish Iron Age BA Joni Karjalainen

1. STONE SLAB
FURNACES
IN THE FINNISH IRON
AGE
BA Joni Karjalainen

2. THE FINNISH IRON AGE AND IRON
• The Iron Age ranges from 500 BC to 1050/1150 AD
• Varies between the regions
• Ends much later than in other parts of main Europe
• Iron probably came from the East
• Contacts already in the Bronze Age
• Similar furnace types from the Republic of Karelia
• Changed livelihoods and beliefs
• Equalized the society as iron ore is easier to obtain
• Especially in Finland it can be found from lakes and bogs

3. LAKE IRON ORE (LIMONITE)

4. TRACES OF IRON SMELTING
• There is very little evidence of furnaces in the Finnish
archaeological record
• But there is slag
• Problematic due to difficulties in dating and identification as
smelting slag
• Few possible furnace bottoms, but they haven’t been
dated properly
• Either they are not recognised or there is so few of them
• Interestingly all definite furnaces are found in Eastern or
Northern Finland
• Considered to be the periphery of the Iron Age
• Only stone furnaces survive

5. STONE SLAB FURNACES
• Built from big slate stone slabs
• Size varies between furnaces surprisingly little
• Partly underground
• Dating in Finland ranges from 400 BC to 600 AD
• They had to work, if they were used for such a long time
• Most fall to the Early Iron Age, 500-300 BC
• There are five definite ”box” furnaces in Finland and
one from northern Sweden (Jernbacken), but the
biggest number of them comes from the Republic
of Karelia, Russia

6. STONE SLAB FURNACES
Riitakanranta (Rovaniemi)
furnace in situ. Photo:
Hannu Kotivuori, Lapin
Maakuntamuseo
Stone slab furnaces
Location Dimensions Slag pit Clay inlay
Kitulansuo D, Ristiina 70 x 50 x 20 cm No Yes
Kotijänkä, Rovaniemi 40 x 50 x 25 cm Yes No
Riitakanranta, Rovaniemi 65 x 32 x 25 cm Yes No
Nastola, Kilpisaari 77-85 x 43 x c. 23 cm No ?
Äkälänniemi, Kajaani 70 x 40 x 25 cm Yes Yes

7. RIITAKANRANTA, ROVANIEMI
Drawing by Hannu
Kotivuori, 1995.
Excavation report,
Rovaniemi 474 a-
c, Korkalo,
Riitakanranta

8. EXPERIMENTATION
• Not really researched through experimental
archaeology
• Few tests or try outs
• Several interesting questions
• Position of tuyere(s)?
• Wind powered or bellows?
• At least two of the furnaces suggest the latter
• Single charge or continuous smelt?
• If continuous, how was it refilled?

9. TODAY’S PRE-EXPERIMENT
• First time using this type of furnace
• Setting:
• Measurements 60 x 40 x 25 cm
• Tuyere and bellows in the middle of a long side
• Clay lining to protect the stones
• Big slate stone as a lid
• Roasted lake iron ore
• Short test with charcoal on Thursday

10. FURNACE