Two Shipwrecks in the Sound of Mull

Duart Castle (Figure 23), ancestral home of the clan Maclean, has watched a great deal of history from its location guarding the Sound of Mull. We have conserved material from two warships sunk in the 17th century whilst attempting to subdue the Macleans. The oldest vessel, the 'Swan', was lost in a storm in 1653. The later vessel, the Dartmouth, sank in a heavy storm on the evening of October the ninth 1690.
Figure 23. Duart Castle
 23
The Swan

Based on the designs of the Dutch pinnaces of the time, she was built for Charles I in 1641. She served the first part of the Civil War as an advice boat carrying messages between royalist forces in Chester and Ireland. When pay ran out, she switched sides, and was finally lost transporting troops in the Sound of Mull for the Commonwealth government of Oliver Cromwell.

When the 'Swan' changed sides the intricate carving from the superstructure, which betrayed her Royalist origins were stowed in the hold (possibly ready for another change of heart or fortune). As a result this has been preserved. Normally the superstructure of a sunken ship is the last part to be buried, and is exposed to aerated water for longer. This allows gribble (limnoria lignorum) and other sea creatures to eat it away.

Much of the carving has been conserved by conventional techniques by Theo Skinner, conservator at the National Museums of Scotland. It was thought, however, that two of the artefacts and some human bone would respond better to Supercritical drying, and these were conserved at St Andrews (Figure 24).

24a 24b 24c
Compass base Cork bottle top Rapier handle
Figure 24. Three items conserved from the excavation of the Swan
The Dartmouth

Designed by John Tippets at Portsmouth in 1655, the Dartmouth was a small, fast warship, used for commerce duties (raiding and protection). She had length at the keel of 80 feet (approximately 24 m), a burden of 266 tuns, and a crew of about 130 men. Whilst the Dartmouth had a long and relatively trouble free history in service, she had a major overhaul at Rotherhithe in 1678, due to an infestation of shipworm (teredo sp.) which was sufficiently bad as to require the replacement of her keel. Her ballast was reported as being bad in November 1688, but this problem ought to have been rectified during a refit at Plymouth in January of 1690.

In October of 1690, the Dartmouth, under Captain Edward Pottinger, entered the Sound of Mull to persuade the Maclean to sign the Articles of Allegiance to William and Mary, by force if necessary. The Dartmouth took emergency anchorage in the Sound during a storm on October 9th, during which she developed a heavy list. Her anchor cables broke at 18:00 hours, and she drifted two miles before striking rocks on the north shore of the sound. The Dartmouth sank with the loss of all but six of her crew.

'The waves beat on her until she went all to pieces there, to the great rejoicing of the Macleans'

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Figure 25. The 'black box', a timber from the Dartmouth, conserved by Supercritical drying. Note the extensive tunnelling by shipworm, exposed by erosion after sinking
We can probably discount the accounts of witchcraft, but the sinking of the Dartmouth does have some unusual features - anchors were found on the ship, but unused. What problem prevented the crew from deploying them? From the historic account, we know that there was a problem with the ballast on the ship in 1688, perhaps this had slipped. Alternatively, the archaeology suggests that the hull may have given way under the pounding of the storm, after having been weakened by shipworm attack.

The Alderney Shipwreck

Dating from the reign of Queen Elizabeth, this wreck was originally thought to be of the pinnace Makeshift, but is now believed to be of a merchantman. Her cargo consisted of large amounts of arms and armour, destined to supply troops engaged in denying Philip of Spain access to French Channel Ports in the years following the Spanish Armada.

41Amongst the material recovered from the wreck in 1995 were some knife and sword handles (Figure 26). These had lost their blades to corrosion, but many retained traces of their tangs, protected by the wood.

Figure 26. A collection of handles with metal wire grips. The first two from the left are weapons (detail - see photographs below), where the wire binding would have helped prevent the user from slipping on a wet handle. From paintings of the time we can guess that the smaller handles to the right belonged to knives that would have hung from the wearers belt, and used as eating implements and general-purpose tools
These artefacts pose problems for conventional conservation techniques. Although good conservation techniques do exist for wood and iron separately, they are mutually exclusive. In consequence, supercritical drying, then an experimental technique, was used in an attempt to conserve the handles as complete units. The photographs below are of these handles after successful completion of the process.
42 43
Figure 27. Once a fine sword handle, this composite artefact contained elements of wood, cloth, copper braid, and the residue of an iron tang
Figure 28. A rapier handle, with only traces of the original braided wire grip adhering to the wood. The dark parallel striations are an image in corrosion product of the original wire

Ecofacts

Ecofacts are frequently as important as artefacts; they constitute general environmental evidence that might be entombed alongside that of human activity. The most commonly analysed material is pollen, which can give a snapshot of the environment in which the activity was occurring. The conifer cone shown here is a macroscopic indicator of the type of environment.

It was also the most complex conservation challenge we have faced to date. In an extremely fragile condition when found, no conservation technique was thought up to the challenge. Upon drying, the cones opened (as a modern cone would). Unfortunately, the greatly weakened core was unable to support the stress of this motion, and the cone collapsed under its own weight. This left discrete piles of bits that had to be cleaned, consolidated and reassembled, as documented in the accompanying photographs.

26 27
1. The cone after drying. It had collapsed and separated into two major parts, the core and the base, as well as many smaller fragments 2. The cone was too weak to move as a complete unit, so many fragments had to be cleaned and consolidated separately
28 29
3. The base was extracted almost complete. Shown here partially consolidated before moving 4. The base was strengthened or consolidated by applying several coats of polymer solution
30 31
5. The core was carefully cleaned and consolidated 6. The base and the core were reunited
32 33
7. Supported in a foam collar, the cone could be tipped to allow re-insertion of the smaller fragments that had been conserved separately 8. Almost finished! Excess polymer was removed by gentle brushing with acetone, to reduce the gloss finish
34
9. The conifer cone after supercritical drying and consolidation

Ecofacts might be as important as artefacts to the scientific study of an archaeological site, but it is doubtful that their display potential warrants the two months of work that was required to complete conservation of the cone above.

SOMAP 98 - NAS training school

The three artefacts below all come from SOMAP 98, a training school run by the Nautical Archaeology Society. The work in the Sound of Mull that August involved surveying the John Preston, a wooden sailing ship that sank with a full load of roofing slates shipped from Port Dinorwic in North Wales, and the Scallastle Bay Cannons, a group of muzzle loading iron guns. The Scallastle Bay Cannons were thought to have been jettisoned by the Dartmouth on October the 9th 1690, just before being blown out of control across the Sound to be wrecked off the mainland coast. The clay pipe fragment excavated from beneath one of the cannon, however, indicates that this ordinance probably dates from after the Napoleonic Wars (early 19th century).

Two of the guns were identified. One is an Armstrong pattern gun dating from about 1785, and possibly manufactured by the Carron Co. (who developed the "Carronade" or "smasher"). The other is a Blomefield gun, which superseded the Armstrong pattern, and was in use up to 1805. As the Dartmouth sank in 1690, these cannot be her guns. The dates of these weapons are consistent with that given by the clay pipe fragment (ca. 1800 to 1830).

ITEM 1: Clay pipe fragment (bowl)
Archaeological Data
Site: Scallastle Bay Cannons Site

Context: Beneath one of the cannons, and possibly dating this site
Notes: The bowl is cast with a raised Hand of Ulster and oval bearing the indented initials (R?) M. Cleaning during conservation confirmed the inscription to be 'RM'. These initials may be scratched in (that is an owners mark), or introduced as part of the casting (a makers mark). The oval about RM is raised from the body of the pipe bowl, and therefore cast with the bowl.
Conservation Data
Lab ref : BA853 External ref : SOMAP 98
Material(s): Unglazed ceramic

Analysis: Gravimetry only, 14.433 g wet weight as origin. Mass loss on acid treatment equivalent to 3% of the original mass. Final dry weight after cleaning 11.158 g (a fairly porous ceramic).

Notes: Item from a seawater environment, stained black with some red/brown colour in patches (iron oxide). Ceramic is robust, but scratched and chipped along the bowl rim, and missing the stem from close to the bowl.
Conservation plan: Full recording, including all dimensions (not shown in accompanying images). Stepwise reduction of salt-water concentration, followed by treatment with 1M hydrochloric acid to remove staining. Complete desalination to chloride free distilled water. Air dry and display.

Plan updates: Hydrochloric acid stripped out iron, leaving clear white ceramic showing in patches. Much of the black colour is, however, a surface bio-film that cannot be removed mechanically. Organic film peeled on drying from acetone, removed by brushing. Some surface damage during cleaning indicated by traces of ceramic powder. Damage is not visible to the naked eye, but may be apparent under magnification. Inscription is now clear, 'RM'.

Current status: Completed
35a 35b 35c
Prior to conservation Close up of initials drawn after cleaning Close up of hand drawn after cleaning
Figure 29. Drawings
36a
 36b
 36c
As origin (wet) After acid wash (wet) After completion (dry)
Figure 30. Photographs
The dark colour of the artefact as it was found (1 above) was due to a combination of contamination, and the darkening effect of water present within the porous structure of the ceramic. One contaminant was iron, derived from corrosion of the cast iron cannon, from below which the pipe was excavated. Iron salts are commonly red-brown in colour, though black iron sulphide may also be formed in reducing environments. The iron salts were removed by washing in hydrochloric acid, the effects of which can be seen in photo 2 above. The other contaminant was a thin organic film on the surface of the pipe. This film was removed by mechanical cleaning in acetone. Small patches of this film are still present in photo 3 above, but the decoration on the pipe (the Hand of Ulster) is now clearly visible.


ITEM 2: Lead Gun Apron
Archaeological Data
Site: Scallastle Bay

Context: Originally associated with cannons, but uncovered between 1997 and 98, and mobile on the sea floor
Notes: Aprons were used to prevent water entering the touch-hole of the gun. When in place the gun could be kept loaded and ready for action. A tampion would have prevented water entering through the muzzle of the gun.
Conservation Data
Lab ref : BA854 External ref: SOMAP 98
Material(s) : Lead

Analysis : Corrosion potential only

Notes : Lead apron is scratched and dented, with some adhering concretion and marine life, but bears no apparent graffiti
Conservation plan: Record - photographic and dimensioned drawings including profiles. Stored in 0.05M sodium sulphate solution in fresh water to prevent oxidation (CP measured = -360 to -375 mV vs. Ag/AgCl). Treat with dilute sulphuric acid (0.5M or 1N) to remove concretion and adherent biological contamination (CP of the Pb in acid with aluminium anodes attached = -650 mV vs Ag/AgCl). Soak in fresh water and dry ready for display.

Plan Updates: Experimental studies confirm that cathodic protection during acid treatment is valuable in preventing the formation of surface lead sulphate. Close anode location allows cleaning to a bright metal surface which acquires a dull white patina over a period of days exposure to air (lead carbonate or oxide). Treatment of the apron revealed large amounts of sulphide salts (presumably iron) embedded within the surface concretions, this results in considerable stench upon treatment with acid (liberation of hydrogen sulphide).

Current status: Completed
                            Figure 31. Drawing               37
38a 38b
Figure 32. Photographs of the apron prior to conservation. Note the apron was moulded to the cannon's shape (left if upper surface, convex)

ITEM 3 : Wooden sheaf
Archaeological Data
Site: John Preston

Context: None
Notes: Of no archaeological value, this item was raised by a sports diver and kept wet in a drain from a domestic sink. The sheaf would have acted as a pulley wheel in a lifting block, as shown in the sketch above.
Conservation Data
Lab ref : BA855 External ref: SOMAP 98
Material(s): Wood

Analysis: Microscopic analysis for species (in progress)

Notes: Very badly worm eaten and contaminated by modern food residues. This is not a nice artefact. It may be useful in evaluating treatments for two other sheaves undergoing conservation at the laboratory, however.

Conservation plan: Record - photographic and dimensioned drawings, wet weight. Treatment with 1M hydrochloric acid to remove iron contamination and sterilise item. Clean than replace all water with methanol and attempt to remove fats. Supercritical drying.
Plan Updates:

Current status: Completed
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Figure 33. Drawing (scale bar is 5 cm long)







40a 40b
Figure 34. Photographs
Above left, sheaf showing screw holes around the large central hole through which the axle would have passed. The screws held a cast iron bearing in place. Above right, view of the other side of the sheaf, showing the triangular recess in which the cast iron bearing sat. The bearing, screws, axle and other iron fittings have corroded away. These photographs were taken before conservation work commenced. Due to the dark colour of this artefact, these photographs have been processed so that detail can be seen.

Ruben Duque 2011. All rights reserved