The burning of seaweed to make kelp was carried out in Orkney from the early 18th century until the early years of the 19th, at which time the industry went into decline.

The shallow waters surrounding Orkney, the sloping beaches and tremendous sea storms made the islands an ideal place to harvest kelp.

Tremendous quantities of tang and ware are washed ashore after the gales that regularly batter the islands, and these were easily gathered up, ready to be burned.

Seaweed had long been gathered by Orcadians, dragged up from the beaches and spread across the fields as a fertiliser.

This tradition was capitalised on by the island lairds, who quickly saw there were profits to be made gathering the seaweed and using it to produce kelp. The ash produced was rich in potash and soda, substances eagerly sought after by the glass and soap industries of the time.

The seaweed was gathered from the shores and laid out to dry, well above the high water mark. The piles of tang were then burned in large, stone-lined pits until the white powdery kelp was all that remained. The remains of kelp pits can be seen clearly today, across many of the north isles.

The remains of a series of kelp pits at the Ness o' Brough in Sanday.

Each kelp fire burned from four to eight hours, assisted by quantities of heather and hay.

The fire was watched constantly by the womenfolk, who ensured it was kept burning steadily. When the blaze was going well, the menfolk would pound the seaweed in the fire, before covering it with stones and turf and leaving it overnight.

The next morning, the chunks of kelp ash were cool enough to be broken into lumps and transported south.

The Orcadian crofters toiled at kelp burning between the months of June and August to subsidise their work on the land.

Undoubtedly hard and backbreaking work, the kelp industry not only caused the health of the workers to suffer but in later years the land became neglected because the lairds had all the islanders working at the kelp.

Stronsay was the first of Orkney's islands to start burning kelp, possibly as early as 1719, when the island's laird - James Fea of Whitehall - brought the practice to the island

To help, Fea brought a Scotsman named Meldrum to Orkney. This Meldrum was supposedly well-versed in the kelp production but it turned out he was something of a charlatan.

Eager to make the most of his position, Meldrum tried to convince the locals that only he knew the "magic words" and had enough of the "magic powder" to make the seaweed burn thoroughly.

Although superstitious, the Orcadians were no fools and paid little heed to Meldrum's wild claims.

Before long, the islands had a thriving kelp industry but its establishment was not without some protest. The opponents of kelp burning claimed that their livestock were being poisoned after inhaling the smoke blowing in from the shore. They even claimed that the limpets on the rocks were dying from the fumes and that the stench was driving away the fish.

The 50 or so years between 1780 and 1830 were Orkney's most profitable, with over 3,000 tones of kelp exported per annum.

The lairds gained most from this, retaining about three quarters of the selling price. Unfortunately, very little of this profit made its way back to the workers.

Kelp burning’s death knell was sounded in the early 1800s when the discovery of mineral deposits in Germany crippled the industry and it went into decline.