The Wooden Objects of Birka – Intact but Fragile

One of the biggest things this year has probably been the huge amount of well preserved wooden artifacts we’ve found. Previous bloggers have already written about the smaller finds we’ve had so far. Many of these finds have been in mint condition, most probably lost during the Viking age by their previous owner. Others have been broken and obviously thrown away. What all these finds have in common, is that they are extremely fragile, even though they look like they were made yesterday.

One of many finds, a needle, that look like it was made yesterday.

All waterlogged wooden objects face similar conservation challenges. Luckily today we know a lot about the conservation methods, but it was not always like this. The pioneers of waterlogged wood conservation were actually the Swedes, during the 1960s, working with the conservation challenges of the Swedish warship Vasa. Vasa faced huge conservation challenges and, at that time, scientists had to draw up new methods in order to solve the problems they were facing. Regardless of size, all wooden objects found at Birka face similar challenges as Vasa, over 50 years ago.

The aim of the conservation is, of course, to preserve the objects as, they were, for future generations so that they can be studied and displayed for the public. In theory this means, that all objects should maintain their original form after the conservation. All waterlogged wooden artifacts face at least two common challenges that have to be taken care of. One is the incorporation of a material into the wood that will give the wood back the structural strength after the destruction of the original cellular structure. The other is the removal of excess water that will prevent shrinkage and distortion of wood. If these steps are neglected, the result is a partial or total deformation and destruction of the artifact.

Uncontrolled drying of the wood will always result in distortions and shrinkage after the water inside the cells starts to evaporate. This is the reason why the cells have to filled with a substance (usually Poly ethylene glycol, PEG) in order to give the wood back its structural strength. The bigger the object, the more time it will take. Vasa was sprayed with PEG roughly 17 years, which was followed by a long and slow drying period of almost 9 years. Luckily our objects are a lot smaller, but nevertheless it is good to keep in mind that all finds have to be taken care of after the excavations, and they will go through proper conservation.

A couple of days ago we found a big piece from a wooden bowl.  It is a good example of an object that looks really robust, but which in fact is really fragile. While underwater archaeologists have the privilege to work in an environment that preserves organic materials really well, we have to always exercise extreme caution while we excavate.

The wooden bowl ready to be lifted.

The bowl was lifted onto a crate and stabilized under water by a wool blanket.

The bowl being registered.

 

Ville Peltokorpi

Pinnar, nålar eller korvpinnar!

Vi har under flera bloggar fått ta del av fina och ovanliga fynd. Jag som registrera allt fynd har förmånen att studera dessa på nära hål. Det råder ingen tvekan om att dessa kommer att stötas och blötas, jämföras och vi kommer att göra djupdykningar i andra material för hitta paralleller.  De kommer att bli uppmärksammade!

 

Redan nu har vi säkert ett 30-tal fynd som vi kallar för nålar. För mig ställer de till en del problem. De är omöjliga att få ner i fyndburkarna. En liten nål kan ta upp en hel låda och att stoppa dessa i påsar går inte heller.

 

Flera utav dessa är svagt böjda och har en skarp spets men inget hål för någon tråd. Det finns även varianter där den är spetsad i båda ändarna. Vad har de använts till vet vi inte. Kanske har det haft många användnings områden?

 

Inom det medeltida materialet kallas de ofta för korvpinnar.  Ett användningsområde för dessa centimetertjocka träpinnar var att hålla köttinnehållet på plats i korvskinnet (fjälstret). Pinnen fästes genom korvskinnet och stängde öppningen. Detta sätt hålla samman korven är känt även från sentida beskrivningar av korvtillverkning.

 

Nu tror inte jag att det är så enkelt att alla dessa pinnar representerar vikingatida korvtillverkning. För oss ligger de nära till hands att även tolka dem utifrån aktiviteter som har skett i en hamnmiljö. Kanske i samband med fiske? Nu kanske vi får tillfälle och närmare studera dessa ganska oansenliga pinnar och bredda deras användningsområde. Intressant är att de ligger i en miljö med ganska mycket djurben dock…

 

 

Tool handles and other wooden artifacts

We have found massive amount of wooden artifacts this year. Spoons, spatulas, nails, pieces of bowls, toggles, tool handles and whole bunch of unidentified wooden things. My favorite find group this year is the tool handles. They are most likely simple everyday tools like knifes and carving blades. Most of them have been perfectly preserved but some are eroded after rolling around on the sea floor before being coated with sediment.

 

Handles have a rectangular hole in the other end where the blade has been attached. We are missing the blades because iron eventually erodes away in the water. Handles are mostly without any decorations. Wood material used for them can be either pine or some harder deciduous trees.

 

Another day I found something quite surprising in the trench. It seems to be a wooden sword handle without any traces of blade in it. Even though it’s quite eroded, one can still see some decorations on the surface.

It remains a mystery if it really is what it looks like. It can be a toy made for a child or as Jim Hanson pointed out maybe a model for a sword handle. Finds of small wooden swords, interpreted as toy swords, has been made also in Hedeby and in Novgorod.

Eveliina Salo

Birka's pole wall

Birka was a trade center and relied on shipping for the conveyance of trade goods. Investment in Birka's harbor would therefore have been of primary importance for the leadership, merchants and consumers alike. Trade during Birka's heyday was no longer limited to small easily portable prestige items, but also bulk items like timber, wool and wheat. This required larger ships (like the knarr pictured below) and therefore larger permanet harbor structures.

 Skuldelev 1 a knarr type trade ship from the Viking Age

Skuldelev 1 from Roskilde Viking Ship Museum.

The safe conveyance of these larger knarr type ships, which primarily relied on sails for propulsion and therefore had smaller crews, speaks to the power of the local ruler and his/her ability to keep the peace. A part of this meant providing a safe harbor for merchants to conduct their trade within the city limits. Remains of the city's defenses are still visible in the landscape today, with parts of the earthern rampart still present around the fortified hilltop of Birka and the remains of the town below.

Photo: Jan Norman Riksantikvarieämbetet.

But the harbor was fortified as well, with an extensive pole wall, which would have controlled access to the harbor, the ships and the wealth within. Not just in the sense of keeping would-be attackers out, but also regulating access and providing a border for the allowance of a custom or tax to trade within the town.

Where we're excavating now is near the outer edge of the pole wall and we have many questions about its construction. Poles are scattered all over the seabed nearby (marked in red on the map below).

Map of timbers in Birkas harbor

Map of pole wall timbers from Birka's harbor. Timbers are marked in red.

The quantity of timbers suggest an extensive construction effort that was no doubt ongoing throughout Birka's history due to the effects of erosion and damage by ice. We don't know how they drove the timbers into the sediment, but an image from Olaus Magnus (though from the 16th century) offers one possible explanation.

Pile Driver Olaus Magnus

Pile driver on ice from by Olaus Magnus 16th c.

We see many different types of construction features on the tops of the poles.

So-called "tapp" from the end of timber 4 first discovered in 2008. Photo: Trevor Draeseke, Sjöhistoriska museet.

Timber 57 (2008) with an eroded construction that probably use to fit with a plank. Burnt on one side. Photo: Trevor Draeseke, Sjöhistoriska museet.

Many of the timbers are also burnt, which could mean a number of things. Perhaps, if the pile driving was being done on the ice, the workers relied on heat and light from bonfires to aid them. Or, if considered with the variety of construction features, these timbers could be secondary use. Given how common damage to buildings by fire was, it is possible some of these timbers used to be part of a building structure and after a fire were moved to the pole wall.

We will document and take dendrochronology samples to try to determine an age range on the timbers. If the pole wall was as important as we think it was, we should see timbers ranging in age of felling across the whole of Birka's period of occupation.

 

Trevor counting growth rings. Photo: Andreas Olsson, Sjöhistoriska museet.