HISTORIC SCOTLAND TAN 13 THEARCHAEOLOGY OF SCOTTISH THATCH
5.3
Dated stratigraphic markers - S Carter
If particular materials can be given a precise date, they can be used to provide maximum and minimum age estimates for undated material stratigraphically above and below. So far only one likely marker has been identified: splleroidal carbonaceo~lsparticles (SCPs). These are microscopic particles produced by the incomplete combustion of coal and oil at high temperatures (Wik & Natkanski 1990). As such. they are a product of recent industrial processes and their abundance reflects the degree of particulate atmospheric pollution. The particles are deposited on ground surfaces and therefore will appear in turves used in thatches. No precise date can be given for their first appearance but they only become common at the end of the nineteenth century and increase in abundance through the twentieth century. Therefore their presence will indicate that a thatch is no earlier than the late nineteenth century. This will assist with the interpretation of radiocarbon dates from overlying thatching materials. Two potential problems should be noted. Firstly, turves under thatch frequently become coated in soot from domestic fires. This soot should not be confused with SCPs but nevertheless, sampling from the surface of a turf protected by an adjacent turf is recommended. Secondly, because SCPs derive from heavy industry they are most common close to major industrial
centres. Deposition of particles in the extreme north and west of Scotland may be too low to be detected and therefore there is potential for a false negative result and an incorrect assumption of an early date.
5.4
Dendrochronology
A thatch will always be younger than the roof timbers that support it so, in theory, dendrochronological dates for roof timbers will provide a maximum age for the thatch. Many roofs may, however, appear older than they actually are due to practices such as the re-use of earlier roofing timbers and the re-cycling of ships . timbers which used to be widespread in Scotland.
5.5
Documentary evidence, architectural style and oral history
Given the relatively recent date of many of the surviving thatched buildings a chronological framework can be constructed using information from available documentary sources, surviving inhabitants and architectural features of the house itself. The quality of this framework can vary significantly from building to building. In some cases the information is sufficient to identify when certain features on the roof were added whereas in others they may only enable us to bracket particular features or materials between two chronologically disparate events. It might be possible,
Pegged joints from a typical Highland building. (B.W.J