Don P
I have red that the black finsh is pine tar, but I doubt that is true after studying the picture more thoroughly. To me it looks more like coal tar, but using coal tar does not make sence to me. Honestly I do not know.
Pine tar mixed with turpentine (not mineral spirit) and either raw or usually boiled linseed oil is a commonly used mixture on many kinds of wooden things. I have used it on the topsides of my boat with good result, for two years until the boat became to rotten because of other reasons.
Pine tar can be used as it is, heated for better penetration or mixed with turpentine.
It is even possible to mix pine tar with red or black pigment in order to get better UV-protection.
It will stay sticky about a year or two, if pine tar is involved in any kind.
Riksantrikvaren (norwegian board of antiques)har an a very practical minded artickle online about use of pine tar on old buildings. It is written in Norwegian, sadly for you Don.
Some more links
Look at the two at the top and the one at the bottom of the page. The dates can be understood even if you do not know Swedish.
http://www.svenskatimmerhus.com/new/tradition.asp?Btn=timmer&SType=main&PageID=historiskaBlannesladu. A hay barn, formerly food storehouse built in the 1290ies
It is in Övre Gärdsjö in Dalarna in Sweden.
http://www.gardsjokultur.se/blannes.htmlTwo storehouses by the church in Älvdalen, Dalarna, Sweden
On the uppermost picure the noe to the left is built in the 1280-ies and the right one in 1577.
http://www.w.lst.se/template/NewsPage.aspx?id=2476The entrance hall from the old church in Rödön, Sweden. When the old church was torn down the entrance hall was moved and reused as a shed. It was originally built in medieval times.
http://www.timmerdraget.org/ click on "Norrlands märkligarte byggnad"
Lagmannsstova, Aga, Hordaland,Norway. Half the upper storey and the stone basement are from the 13th century
http://nn.wikipedia.org/wiki/Agalook at the pictures of lagmannsstova
http://www.touristphoto.no/ullensv6.htm