The History of Seaweed in Scotland: Kelp, Iodine and the Shore That Fed an Industry

By Jayson Byles, forager & chef · September 2026

The history of seaweed in Scotland runs from Neolithic teeth in Orkney, through a kelp-burning industry that is said to have begun on the Fife shore in the 1690s, to the discovery of iodine in 1811, a twentieth-century alginate industry and a wartime hunt for agar on the Clyde. It is a working history: for most of it, seaweed was fertiliser, glass and medicine before it was dinner.

We cut seaweed on the Fife coast for a living, so this is our patch of that story. The wracks we harvest for the workshops are the same plants that were raked, dried and burned here three centuries ago, and the iodine that makes people careful with kelp today is the element that gave the industry its second life. This page is the history spoke of the other uses of seaweed; the sister pages on nutrition, medicine and what comes next pick up where it ends.

Before kelp: food and fodder

The oldest evidence is in teeth. Hardened dental plaque from two teeth at Distillery Cave in Oban and eight teeth from the Isbister chambered cairn in Orkney shows people eating seaweed in the Neolithic, between 4,500 and 6,100 years ago, and isotope work on Neolithic Orkney bones shows more than half the sheep analysed were eating it too, as winter fodder when the fields ran out (Dig It!, Dr Magdalena Blanz). The Slow Food Ark of Taste entry for dulse puts the earliest recorded harvesting of dulse with the Irish monks of Saint Columba's era, more than 1,400 years ago, and notes it became a fallback food for Scots pushed to the coast in the nineteenth and twentieth centuries (Slow Food UK).

Two habits from that long prehistory survive in plain sight. Storm-cast kelp is still forked onto the machair in the Uists as fertiliser, a tradition the Scottish Parliament's own briefing calls continuous (SPICe, 2018). And on North Ronaldsay the sheep still live on the shore and eat the weed, for reasons that belong later in this story.

Kelp begins on the Forth

"Kelp" did not originally mean the plant. It meant the ash: seaweed dried, burned in a shallow stone kiln and raked into a hard, bluish slag that was sold to glass and soap works for its soda and potash. Chemistry dates the trade: kelp-fluxed glass carries far more strontium than wood-ash glass, and Yorkshire glass of 1655 to 1670 has the seawater signature. Christopher Merrett described kelp in English glassmaking in 1662 (Dungworth, 2009). On our side of the border a 2025 study of seventeenth-century Scottish window glass records the botanist John Ray watching kelp and sand being mixed at a Forth glassworks in 1661, and a dispute at the Leith glassworks settled in 1664 with a payment of five shillings and fourpence for kelp (Post-Medieval Archaeology, 2025).

Against that background the usual account, that organised kelp burning began in Fife in the 1690s, reached Orkney in the 1720s and the west coast in the 1740s, makes sense: the Forth had the glassworks, Fife had the rocky shore and the wrack (Except the Kyles and Western Isles, 2018). We have not found a primary document naming the first Fife kiln, and we say so. What is well recorded is the next step. James Fea of Whitehall on Stronsay made the first Orkney kelp in 1719 by one account and about 1722 by another, and by 1742 the smoke was blamed for failed harvests: on Sunday 16 May that year around fifty islanders rioted against the kilns (The Orkney News, 2025; Archaeology Orkney).

The boom, 1780 to 1830

Kelp was worth about £3 a ton in 1750. The wars with France closed off Spanish barilla, the purer competitor, and by 1810 the price was above £20 (The Past). It took ten to twenty tons of wet weed to make one ton of kelp, cut and carried by whole families through the summer, and a kiln burn could take a day of stirring. Orkney alone shipped around 3,000 tons a year between 1780 and 1830, about two thirds of the islands' exports. The workforce is harder to pin down: around 3,000 people in Orkney; around 10,000 families across Scotland by one archaeological survey; 50,000 people by the Scottish Seaweed Industry Association's history (SSIA). For two generations the shore was the main employer of the Atlantic and Northern Isles coasts.

The wrack that fed the kilns was ours: bladder wrack and serrated wrack and the knotted wrack of the sheltered lochs, cut at the spring tides and dried on the turf. Kelps such as oarweed came in as storm cast, "tangle" to the kelpers, and drift tangle fetched about twice the price of cut weed on North Ronaldsay in the 1860s and 1870s.

Collapse, and what it did to people

After Waterloo the duties that had kept foreign alkali out were lifted, and the price fell as fast as it had risen: back to £3 a ton by 1827, £2 by 1831 (The Past). Cheap Leblanc soda finished the job. Landlords had subdivided crofts and encouraged large families to keep hands on the shore; when the money stopped, the people were still there. The Scottish History Society's account of the Clearances puts it in one sentence: the end of the Napoleonic wars "brought tumbling prices, returning soldiers and a swift end to the dominance of kelp in the Highland economy" (Scottish History Society). Emigration followed.

North Ronaldsay shows the mechanism in miniature. The kelp slump left the island with more people than work, and the laird set the spare labour to heightening the wall around the whole island, finished in 1832, so that the native sheep could live entirely on the shore and the fields inside could be improved (Orkney Sheep Foundation). The same year thirty-two families were moved off the island to Eday (Orkney Seaweed Stories). The sheep are still out there eating seaweed, and the last kelp was burned in Orkney in 1937.

Who discovered iodine, and how kelp came back

Iodine was found in kelp ash, by accident, in a saltpetre works. Bernard Courtois, making potassium nitrate for gunpowder from seaweed ash because wood ash was short, noticed that something in the ash was corroding his copper vats. In 1811 he added sulphuric acid to the residue and a violet vapour rose and condensed as dark crystals. The element was announced in 1813; Gay-Lussac named it from the Greek for violet, and both he and Humphry Davy credited Courtois with the discovery (Linda Hall Library).

That gave the Scottish kilns a second market. From the 1840s kelp was bought not for soda but for iodine, and Glasgow became the centre of British iodine production, drawing kelp from the Hebrides and Ireland up the Clyde: about 6,000 tons in 1845 and 10,000 tons a year by the early 1860s (Except the Kyles and Western Isles, 2018). The chemist Edward Stanford, who published On the Economic Applications of Seaweed in 1862, arrived on Tiree in 1864 to build a factory at Middleton, known locally as the Glassary, which extracted iodine from the tangles until 1901 and sold the leftover charcoal as fertiliser (An Iodhlann, Tiree). In 1883 Stanford isolated alginic acid from kelp, the compound that would matter most in the next century (Grace's Guide). Cheap iodine from Chilean nitrate deposits undercut the kelp works from the 1870s, and the trade dwindled again.

The twentieth century: alginate and wartime agar

Stanford's alginic acid became an industry in the 1930s, when a company called Cefoil started producing alginates at Bellochantuy in Kintyre. During the war three more factories went up at Kames and Barcaldine in Argyll and at Girvan in Ayrshire; after 1945 Cefoil bought them from the government and became Alginate Industries. It built its first Hebridean plant in South Uist in 1944, another at Sponish in North Uist in 1955 and one at Keose on Lewis in 1965, where cut wrack was dried and shipped to Girvan. By 1973 Girvan employed 650 people and Barcaldine 250. Kelco of California took the company over in 1979; the Hebridean plants closed, and Barcaldine shut in December 1996 with the loss of its last eighty jobs (Grace's Guide; Hebridean Connections; Uist Asco). Alginate production carried on at Girvan under later owners until 2009, when manufacture moved to Norway. What alginate does in a wound dressing or an antacid is the subject of our medicine page.

The war produced a smaller, stranger episode. Japan had supplied the world's bacteriological agar, and with Japan on the other side Britain had none for culture plates and vaccines. From the Marine Station at Millport, Sheina Marshall and A. P. Orr surveyed the Firth of Clyde in 1942 and the west coast islands in 1943 and found that the red seaweed Gigartina stellata, a relative of carrageen, would gel well enough for a British agar. The Ministry of Supply wrote to thank them; demand fell away after the war (Coast, SAMS). Millport's successor, the Scottish Association for Marine Science in Oban, now runs two research seaweed farms.

One more Briton belongs here, though she never worked in Scotland. In 1949 Kathleen Drew-Baker of Manchester published in Nature the hidden life cycle of Porphyra, our laver and Japan's nori. Her paper made reliable nori farming possible; Japanese growers built her a memorial in 1963 and still hold Drew Day on 14 April (Science and Industry Museum).

Seaweed in Scotland now

The industry that remains is small and growing. The Scottish Government's 2022 study put it at roughly £4 million of turnover and 59 jobs, with scenarios running to £22 million a year by 2040 on wild harvest and £71 million with farming added (Scottish Government, 2022). Oceanium in Oban biorefines farmed kelp into food ingredients; Marine Biopolymers in Ayr works with alginate; the Hebridean Seaweed Company processes wrack on Lewis, where the Alginate Industries lorries used to run. In November 2025 a UK-wide body, UK Seaweed, was launched at the Scottish Seaweed Industry Conference in Oban to speak for farmed and wild-harvested seaweed together (UK Agri-Tech Centre).

The rules have changed too. The kelpers took what the laird's shore gave; anyone harvesting beyond personal use today needs a Crown Estate Scotland licence, explained in our plain guide to the law. What has not changed is the plant, the tide and the work of cutting. Our complete guide to seaweed foraging in Scotland is the place to start, and the pages on what seaweed gives you and what the supplement label leaves out carry the iodine story into the present.

Sources

• The archaeology of Scotland's natural larder: seaweed (Dig It!, Dr Magdalena Blanz)
• Dulse, Ark of Taste (Slow Food UK)
• Kelp harvesting, SPICe briefing SB 18/75 (Scottish Parliament, 2018)
• Innovations in the 17th-century glass industry: the introduction of kelp ash in Britain (David Dungworth, Verre et Histoire colloquium, 2009)
• Composition of late seventeenth century window glass from Scotland (Post-Medieval Archaeology, 2025)
• Kelp part 1: from soda ash to iodine (Except the Kyles and Western Isles, 2018; secondary account citing Stanford 1862 and the Napier Commission)
• Stronsay's kelp riots (The Orkney News, 2025)
• North Ronaldsay's kelp industry in the 19th century (Archaeology Orkney)
• Sifting through the remains of Scotland's kelping industry (The Past)
• History of Scottish seaweed (Scottish Seaweed Industry Association)
• The Highland Clearances (Scottish History Society)
• The dyke: origin (Orkney Sheep Foundation)
• Fire (Orkney Seaweed Stories)
• Bernard Courtois, Scientist of the Day (Linda Hall Library)
• Edward C. Cortis Stanford, Tiree, 1837 to 1899 (An Iodhlann, Tiree's historical centre)
• The history of alginate extraction, by Jim Bailey (Grace's Guide)
• Alginate Industries (Hebridean Connections)
• History of seaweed collection and its processing in North and South Uist (Uist Asco)
• Seaweed at SAMS in wartime and today (Coast)
• Kathleen Drew-Baker (Science and Industry Museum)
• Understanding the potential scale for seaweed-based industries in Scotland (Scottish Government, 2022)
• UK Seaweed launch unlocks new growth opportunities (UK Agri-Tech Centre, 2025)

Questions we get asked

When did the Scottish kelp industry start?

Kelp, meaning seaweed ash for glass and soap, was being bought at Forth glassworks in the 1660s, and organised kelp burning is usually said to have begun in Fife in the 1690s. James Fea made the first Orkney kelp on Stronsay between 1719 and 1722, and the trade reached the west coast in the 1740s.

Why did the kelp industry collapse?

Prices fell after 1815, when the end of the wars with France let cheap Spanish barilla back in and the duties protecting kelp were lifted; Leblanc synthetic soda then replaced both. Kelp that fetched over £20 a ton in 1810 was worth £3 by 1827 and £2 by 1831, and the coastal populations built around it were left without work.

Who discovered iodine, and what has it to do with seaweed?

Bernard Courtois, a French saltpetre maker, found iodine in seaweed ash in 1811 when sulphuric acid released a violet vapour from the residue in his vats. Gay-Lussac named it in 1813. From the 1840s Scottish kelp was burned again for iodine, with Glasgow the centre of British production until cheap Chilean iodine undercut it.

Was kelp burning linked to the Highland Clearances?

Yes, indirectly. Landlords had subdivided crofts and kept large populations on the shore to supply kelp labour. When prices collapsed in the 1820s those tenants could not pay rent, and clearance and emigration followed. North Ronaldsay's sheep dyke, finished in 1832 by surplus kelp labour, and the removal of 32 families to Eday that year show the pattern.

Is seaweed still harvested commercially in Scotland?

Yes, on a small scale. The Scottish Government valued the sector at about £4 million and 59 jobs in 2022; alginate has not been made here since Girvan stopped in 2009, but wrack is processed on Lewis, farmed kelp is refined in Oban and hand-harvesters like us cut for food and raw material. Wild harvesting beyond personal use needs a Crown Estate Scotland licence.