Surveying the Swan: archaeological techniques under water are the same as on land. (Photo: Colin Martin)
In 1653, a small Cromwellian warship was lost off the west coast of Scotland. Excavated between 1992 and 2003, the wreck of the Swan yielded finds that tell stories of cutting-edge weaponry, mishaps on board, and plunder. Now the full report has been published, Colin Martin reveals the ship’s secrets and explains why wrecks are such a valuable archaeological resource.
Buried beneath the waves around the British Isles are many lost vessels, each with a number of characteristics that make them archaeologically special. First, a shipwreck provides a watertight (forgive the pun) context. Everything in it was associated with a self-contained, functioning entity at the moment of loss and deposition. Sometimes the identity and background of a wreck will be known from historical sources; otherwise dating will depend on typological studies (of coins, pottery, clay pipes, and so on). However obtained, once a date is established for the site as a whole, contextual association will extend that date to everything it contains. The value of this for checking and refining artefact typologies is unparalleled, with the only caution to be observed being the possibility of later contamination, although proper archaeological procedures should negate this risk. A shipwreck has contexts and stratigraphy, just as any site on land.
Just how comprehensive and revealing shipwreck assemblages can be is demonstrated by major maritime archaeological discoveries such as the Mary Rose or Vasa, but every historic wreck can contribute to wider archaeological studies. Take the case of the Swan, a small Cromwellian warship lost off the west coast of Scotland in 1653. She had been part of an expedition to nip a Royalist revolt in the bud. While attacking the Maclean stronghold of Duart Castle on a headland overlooking the Sound of Mull, the ships were dispersed by a violent storm. Three were wrecked. The Swan’s remains were discovered in 1979, and the site was later designated a protected historic shipwreck. In 1992, erosion began to expose vulnerable archaeological deposits, and a controlled programme of partial excavation, consolidation, and protection was completed in 2003 (see CA 197). The results have recently been published.
These three pewter ‘tappit hens’, or Scots liquid measures, are the earliest examples known. The small blobs inside the necks indicate certified levels. (Photo: Colin Martin)
Several unexpected and revealing archaeological byways were opened up in the process. Excavation revealed three pewter flagons of a distinctive Scottish type known as ‘tappit hens’. What is remarkable about these pieces is that their secure terminus post quem of 1653 identifies them as the earliest tappit hens known to exist. Pewter is a soft alloy easily damaged in use, so items are frequently recycled, explaining a dearth of early examples. But catastrophic loss, like a shipwreck, freezes them in time.
A clue concerning how the flagons came to be on the ship is scratched on the base of the chopin (1/2 pint) measure. The mark can be identified as a ‘mountain inflamed proper’: the crest of the Mackenzie clan. It symbolises the network of fire beacons in the Highland landscape that linked a maritime clan’s castles to its galley fleets. Prior to the Cromwellian fleet’s arrival at Duart, it had seized two Mackenzie castles, and it is likely that this item was plunder from one of them.
More significantly, these finds have shown pewter experts that 17th-century tappit hens were manufactured using a different technique from that of later periods. Because early examples had not been examined, this was not previously known. By the start of the 18th century, the distinctive tripartite shape was made up of three moulded circular pieces, joined around their horizontal seams. Base, handle, and hinged lid were added at the end. The Swan examples, in contrast, were cast as two semi-circular vertical halves. The base element was an integral part of each casting, and each had a semi-circular cut-out in the centre. When the sections were joined, a hole was left in the base, which was used, together with the narrow mouth, to centre the vessel against the headstock and tailstock of a lathe. This enabled the exterior of the body to be finished by turning, followed by burnishing to give its surface a high polish. Finally, the hole in the base was filled with a plug, the inside of which bore an enlarged version of the pewterer’s mark.
Analysis has shown that this cast-iron gun was made using revolutionary techniques. It is a lightweight type called a drake, and is still in exceptionally good condition. All recoveries from the wreck are curated by the National Museums. (Photo: Colin Martin)
The investigation of one of the ship’s guns has thrown unexpected light on the technicalities of early modern metallurgy. Seven iron guns lay exposed on the site at the time of discovery. They were heavily concreted and evidently much corroded, so a decision was made to leave them in place, and they now serve as waymarks and points of interest on a heritage trail set up for visiting divers. During the excavation of the collapsed stern structure, however, a small iron gun was found buried and in good condition, together with its wooden carriage. Both have been raised and conserved.
When a light covering of concretion had been removed from the gun, it was found to be in pristine condition, with the wipe-marks from the clay casting pattern still crisp on its surface. Cut into the breech are the initials of the founder, identified as John Browne of Horsmonden in Kent. Its weight is marked as 4151bs (188kg), and a modern weighing with the concretion removed showed that the piece had lost only 1.7% of its original weight to corrosion – an extraordinarily low figure for iron that had been immersed in oxygenated seawater for three-and-a-half centuries. Analysis of the metal by Dr Ian Macleod of the Western Australian Museum and Professor Hans Preβlinger of Vienna revealed that it had strength and resistance to corrosion similar to that of modern cast steel. But their studies show that these properties were not achieved by extracting the impurities, as is done today, but by adding just the right balance of neutralising substances to counteract them. How a 17th-century Kentish iron-founder gained the knowledge to do this remains a mystery.
The drake’s inverted carriage was found nearby. (Photo: Colin Martin)
Much is known from documentary sources about John Browne and the excellence of his work. During the early 1620s, a new type of lightweight gun called the drake was introduced to England and, as master-gunfounder to James I and Charles I, Browne was its principal manufacturer. Drakes were much shorter than conventional guns, which saved a good deal of weight, but their lightness mainly depended on their tapered powder chambers. This was not to reduce the gunpowder charge, as often supposed, but tapering the chamber allowed the outer part of the breech – the rear portion of the barrel- to be reduced in diameter while still remaining strong at the point of maximum pressure. Finally, Browne used what he described as ‘refined’ iron for his castings, and charged double for it. It has been suggested that this saved weight because it was a lighter alloy, but we now know that it was not lighter but much stronger, so less was needed. In combination, these factors meant that the weight of drakes was less than half that of other guns of the same calibre. The Swan piece is the only cast-iron drake by Browne known to exist, so analysis of this find has cracked a 350-year-old industrial secret.
This is an extract from a feature published in CA 329. Read on in the magazine. Click here to subscribe.