A VIKING WHITEWASH
Article created on Sunday, October 13, 2013
It was already known that Iron Age Danes whitewashed their houses and halls with lime to protect clay walls against wind and weather. However it wasn’t clear whether they created their their own lime, or if it was sourced from elsewhere.
Now Danish National Museum archaeologists have found the answer in the rich Viking settlement at Tissø, Zealand. In the spring of 2013 they excavated the first lime kiln from the Danish Late Iron Age, the oldest found in Denmark.
The base of the lime kiln, which is carbon-14 dated to about 850 AD Photo: National Museum.
Burning slaked lime
The researchers examined a kiln used to burn slaked lime around the the middle of 800s CE. National Museum archaeologist Sandie Holst explained that, “We knew in advance that the great halls and buildings of Fuglede farmhouse were whitewashed because of previously excavated daub with traces of white chalk, but now we have proof that the limestone was burned in the immediate area” .
The excavation uncovered only the base of the kiln, which first appeared to be a hard layer of lime mixed with charcoal several centimetres thick. Under this layer was sand burned red due to the heat that it had been exposed to. At first, archaeologists thought the thick layer was just solid ash, but the layer was rock hard and seemed to consist of something more than just ash and charcoal.
Fragment of “slaked” lime from 850 CE Photo: National Museum
National Museum agronomist Peter Steen Henriksen therefore examined a sample. – “I always have my microscope with the excavation, and when I looked at the sample, it looked like so much lime. Therefore, I bought some hydrochloric acid and dripped it on the sample that reacted exactly as lime reacts when exposed to acid – it seethed and bubbled merrily, he said.
To prepare the whitewash you have to burn limestone, travertine or seashells to temperatures of more than 900 degrees which converts limestone to calcium oxide. The lime is slaked by adding water, creating calcium hydroxide, which is highly alkaline and highly corrosive. This slaked lime is further diluted with water ready to whitewash walls.
It is a dirty and dangerous task to burn lime, even if you inhale the dust or get it in your eyes, it will react instantly with moisture and cause damage.
Currently the team are unsure where the occupants of the site at Tissøs collected the raw materials for lime burning but clearly they required large quantities of wash to maintain the many square metres of wall in the huge Viking halls, which had floor plans of over 500 square metres.
A long history of whitewash
Archaeologist Sandie Holst explained that, “beyond the practical reasons, it was probably also a status symbol to have whitewashed houses and halls”.
“Discovery of daub from the Iron Age and the Bronze Age with traces of white chalk shows that Denmark has washed its homes in more than 2000 years before the Danish Late Iron Age burned lime at Tiss”, she said.
What amazes her is that it has taken so long to find one, though she is convinced that there are many more kilns to find.
Source: National Museum of Denmark