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Armada Cannons and Gun Carriage Wheel

Read about the first steps towards the conservation of nine cannons, a copper alloy cauldron and a gun carriage wheel recovered from the wreak of La Juliana off the coast of Sligo.

In the summer of 2015 the Underwater Archaeology Unit (UAU) of the National Monuments Service gathered together an expert dive team to carry out a detailed survey and rescue excavation of a wreck site off Streedagh Strand, County Sligo. Successive storms off the west coast during the winters of 2014 and 2015 had caused sands to shift, potentially exposing three wrecked ships of the Spanish Armada. A preliminary investigation by dive teams in April 2015 located the remains of La Juliana, an 860 ton merchant vessel, requisitioned to carry 32 guns, 325 soldiers and a 70 man crew during the 1588 Armada campaign (Moore, 2015). 

  Cannon on the seabed. Courtesy of the National Monuments Service, Department of Culture, Heritage and the Gaeltacht Cannon on the seabed. Courtesy of the National Monuments Service, Department of Culture, Heritage and the Gaeltacht

It became evident to the dive team that objects of interest associated with the wreck of La Juliana were exposed, vulnerable and in need of immediate recovery. 

Two cannons after recovery from the seabed Gun carriage wheel on the rescue boat

Cannons and gun carriage wheel on deck after recovery from the seabed.

Nine cannons, one copper alloy cauldron and an eight spoke gun carriage wheel were recovered from the sea bed it and transported from Streedagh, County Sligo to the National Museum of Ireland for conservation treatment in Dublin.  

Cannon arriving in Dublin, lifted from flat bed truck Cannon placed in steel storage tank.

A cannon arriving in Dublin and lifted from a flat bed truck into a steel storage tank.

Conservators are working to make the armada collection accessible to all who want to understand and appreciate them, both now and in the future. As a department we have previous experience treating armada cannons. On display in the Museum of Decorative Arts and History, Collins Barracks are two guns, a siege cannon and a smaller pedrero.

The larger of these cannons, the siege cannon, was recovered from the Spanish Armada wreck of the Trinidad Valencera, off the coast of Co. Donegal. The Trinidad Valencera was a Venetian merchant ship that had been seized in Sicily in 1586 and forced into the service of Philip II of Spain. At 1,100 tonnes she was the fourth largest of the ships of the great armada of 1588, with which Philip tried to invade England. After a battle with the English and a violent storm, many ships from the fleet were wrecked around the Irish coastline.

The siege cannon was cast in 1556 by the Founder Royal, Remigy de Halut, in Brussels. It bears an inscription stating who made it, together with the arms of Philip II and is decorated with dolphins and stylised foliage. It is bronze, weighs 2.5 tonnes and would have fired a 41 lb iron ball. This was one of a number of siege guns that the 130-ship armada carried in preparation for the proposed conquest of England, together with 19,000 soldiers and their supplies.

The smaller ‘pedrero’ cannon from the Juliana was recovered off Streedagh Strand in Co. Sligo. The Juliana was one of three Armada vessels wrecked on this part of the coast in the storm of 21 September 1588, where they broke up and where the bodies of 1,000 crew members were later found.

                Figure of a saint on the barrel of the pedrero Pedero cannon in the conservation lab

                    Figure of a saint on the barrel of a pedrero in the conservation studio.

The pedrero cannon was small and comparatively light in weight. It fired a large stone ball and would have been a ferocious weapon at close quarters in ship to ship fighting.

When the cannons were raised, they were completely impregnated with salt from the sea. Salt, when combined with oxygen and water in the air, causes rapid corrosion in metal, so the salt had to be removed before the cannon could be dried out. This was achieved by placing the cannons in tanks of fresh water, alternating between hot and cold to make the metal expand and contract to force the salt out. The last two washes were carried out with de-ionised water, to ensure that the salt content of the cannons was as low as possible.

Changing tank storage water Cannons in heating tank

Changing storage tank water. The cannons on the right are housed in a tank designed to heat the storage water.

The cannons were then dried out thoroughly and the painstaking work of cleaning off corrosion and concretions could begin; a process which took several weeks. The layers of dirt and corrosion had to be carefully removed mechanically with hand tools to reveal the original surfaces of the cannons under them. Several coatings of corrosion inhibitor and lacquer were applied, followed by a coating of wax to protect the cannons while on exhibition at Collins Barracks. 
The conservation of the nine cannons is ongoing. The conservation of the gun carriage wheel will be a three phase process:
1. Concretion removal and desalination. 
2. Consolidation 
3. Conservation mounting with recommendations for storage and display.  
Phase one has started.        
 The wheel supported within a protective cradle ready for transport Wheel before concretion removal
The wheel packed and supported within a protective cradle, ready for transport. Right, the wheel before conservation
Concretion removal and desalination
Marine archaeological objects are often hidden by thick unsightly concretions that obscure its true form and construction, and the carriage wheel is no exception. It is covered in a concretion which grew from iron on the wheel rim and wheel hub corroding and interacting with the surrounding environment to create a hard, compact mass of sediment, stones, corrosion product and marine organisms. To reveal the true nature and size of the wheel, the concretion has to be removed.
The wheel is kept wet during remedial work Variety of hand tools
The wheel is kept wet during remedial conservation. Concretion is removed with a variety of hand tools.
Concretion removal is painstaking work. Concretions are by their very nature hard as rock and the wood underneath can be as soft as butter, so great care has to be taken.  A variety of hand tools are used such as hammers and chisels on the thicker harder areas, proceeding to an air scribe for finer detailed work.
Concretion removal, session 1 Concretion removal, session 4 Concretion removal, session 8
Removing concretions from the wheel will also hasten the process of desalination. Once the conductivity of the storage solution reaches a sufficiently low level, the wheel will be classed as desalinated and made ready for phase two to begin. 
Further reading
Moore, F. Brady, K and Kelleher, C. (2015) Cannons, Saints and Sunken Ships— an Armada Wreck Revealed, Archaeology Ireland, Winter 2015, p.10-15. 
Pearson, C. (1987) Conservation of Marine Archaeological Objects, Butterworth & Co.
Luka, B. (ed) (2014) Conservation of Underwater Archaeological Finds Manual, International Centre for Underwater Archaeology in Zadar, Zadar Croatia