Our Kelp in Ages Past
26 September, 2013
Last week I was at Tantallon Castle in East Lothian, the site of a planned archaeological investigation in the coming weeks. The castle grounds recently underwent resistivity and magnetometer geophysical survey or ‘geophys’ to use Time Team jargon. This revealed a number of interesting geophysical ‘anomalies’ indicating possible sub-surface features such as buried wall-lines and ditches.
The planned archaeological investigation involves excavating a series of small trenches across some of these anomalies to explore the grounds in detail. This, we hope, will increase our knowledge of the castle, filling in some of the gaps in its long history, and inform our interpretation of the site.
The castle sits within a Site of Special Scientific Interest, so we are required to consult with Scottish Natural Heritage and satisfy them that we are not going to damage the wildlife. The grassland around the castle is unimproved neutral grassland – that is, it has never been artificially fertilised for agricultural purposes. This is a rare habitat, important for wild flowers and the insects, particularly butterflies, which it supports.
In last week’s post I wrote about seals, and there are many seal colonies around the coast and islands of Tantallon Castle, where they feed among the kelp beds. Kelp is a seaweed that attaches itself to rocks and stretches like a long scarf, up to 30 metres, reaching to the surface. Looking to sea from the castle at low tide, you can see the kelp forests lying off the rocks of the point. They are used for shelter by many sea creatures and seals often hunt for fish within them.
In the past, these seals would have been hunted by local fishermen. They would have provided many useful commodities, including blubber. At this time of year, the seals have built up large fat reserves to see them over the winter. This thick layer of fat, just below the skin in seals and whales, is known as blubber. Blubber can be melted to produce an oil, which was the main product of the historic whaling industry. Blubber was also particularly effective as a lubricant before its use was banned (the last whale-oil lubricant was sold in America in the late 1970s). It was a good fuel for lamps – though many households would also have refined sheep or beef tallow to burn in lamps. Fish oil was also used, but it was smelly and dirty to burn. Among the artefacts found around Tantallon Castle was a stone oil lamp, recovered from the beach below the castle in the 1920s. The lamp has a bowl for the oil and a groove for the wick.
But kelp did not merely act as a bait for seals and other sea life. Historically it was used in many ways. From early times, it was used as a fertiliser, spread raw on the fields. During the 1600s, it began to be burned as a source of soda and potash. Over time, this became it became a major additional source of (tax free) income in the Highlands and Islands of Scotland.
Soda and potash were important chemicals in the soap and glass industries and were widely used for linen bleaching. The extraction process involved burning the kelp in large, often stone-lined trenches – or circular pits in Orkney.
You can see kelp pits at the Links of Noltland on Westray, Orkney. Here, it was burned for some four to eight hours, the fire kept going with the help of heather and hay. It would then be covered with stones and turf to protect it against moisture, and left overnight. The following morning the chunks of kelp ash would be cool enough to be broken up into lumps for transportation. This industry continued until the early 1800s, when the discovery of mineral deposits of potash in Germany put an end to it, though on Orkney it continued into the late 18th and early nineteenth century.