(04 march 1998)
Due to the great number of excavated artifacts, the Centre de conservation du Québec has established partnerships with other conservation laboratories such as the Canadian Conservation Institute and Parks Canada. The Service Centre of Parks Canada in Ottawa was given approximately 60 heavily concreted artifacts excavated during the summer of 1996.
All of the objects were X-rayed, most from several angles, to determine if the materials within the concretions had survived and, if they had, what condition they were in. If a concretion was hollow, sometimes the impression of the original object remained and could be moulded by injecting rubber or epoxy into the void, then breaking apart the concretion. Various objects were visible in some of the concretions, including rifles, shoes, pieces of metal, textile, leather, and wood, and a large metal
cauldron.
The State of the Cauldron before Restoration
The X-rays of the cauldron were inconclusive due to the thickness of the concretion on the exterior surface and the fact that the pot was at least half-filled with concretion. They showed no solid metal contents and the metal of the cauldron itself was very poor. No recognizable objects could be seen in the X-ray of the interior. A large piece of concretion had broken off the cauldron during underwater excavation, separating with it two large sherds and leaving another sherd attached to another concretion. In the interior, the top of a folded piece of textile could be seen as well as one other possible leather or textile fragment. There appeared to be two handles but they were also concreted over and their condition was unknown. The walls of the pot appeared to be 5 to 8 mm thick. There were no feet visible in the concretions.
The Restoration of the Cauldron
The pot was stored in a 500-Litre tank in a 0.5% solution of Hostacor KS1 (a corrosion inhibitor) in tap water in a walk-in fridge at 3°C. A plywood cradle was made to hold a large shallow plastic tray lined with Ethafoam padding material to support the cauldron when it was being worked on and or moved in and out of the tank. Two people were required to lift the object as it weighed approximately 70 to 80 Kg.
We decided to mechanically excavate the interior of the pot in an effort to determine what the visible concretion/textile was. Although we had successfully used a Cavitron dental tool and also a pneumatic tool to help remove concretions from most of the rifles, the Cavitron proved generally ineffective (too slow) against most of the concretion in the interior of the pot. A small chisel and mini-hammer were therefore used to remove much of the concretion, until what appeared to be a small bristle from a brush was visible near the bottom. By slowly detaching the concretion with the Cavitron and a very small chisel, more pieces emerged, which Marc-André Bernier then recognized as small fish bones, possibly cod. Further removal of the concretion began to show larger fish bones. The soft tissue of the fish had been replaced by silt and rock but the bones remained in-situ until exposed. Great care must be taken when using mechanical tools such as a chisel or Cavitron since the surface of the pot is softer than the concretion and is easily damaged.
As more of the interior concretion was removed, the corresponding exterior concretion was also removed to reduce the weight and stress on the walls of the cauldron. The exterior concretion was extremely easy to remove by splitting small sections then prying under them and lifting them off. The underlying surface appeared in very good condition. After detaching the concretion from the rim, it was obvious that some rim pieces were cracked and loose. These were separated from the rest of the pot by simply removing the attached concretions and "wiggling" the sherd until it came off. All removed sherds and the two larger body sherds previously separated were stored in 0.5% Hostacor KS1. As more of the exterior concretion was removed, close examination of any of the exposed surfaces revealed a network of cracks over the entire pot. It was not clear if these cracks were the result of vibration caused by the removal of the concretions, a product of stresses caused by simply moving the pot, a pre-existing feature or a combination of all three. The walls of the cauldron easily flexed and the cracks got larger or smaller as slight pressure was applied near them.
Since one side and part of the base of the pot were missing, it was known before we started that the pot might break apart once the concretion was removed. Initially, as the top of the cauldron was separated from the concretion, a layer of coated wire and tape was wrapped around the top. Suggestions were made to cover the exterior (once it was fully exposed) with a support coating of polyester, epoxy, bandages or other material over a barrier coat. However, due to the difficulty of removing most applied coatings later and the fact that the tape seemed to be working well, no other support mechanisms were used. The thick concretions on the exterior bottom of the cauldron were left in place, not only to support the pot but also to protect any feet that remained. Similarly, the concretions around the handles were left in-situ to protect them.
Although cast iron pots of this era are extremely rare, it is known that they usually had three legs. The concretion at the bottom of this cauldron has not been removed yet and there is a possibility that one leg may have been attached to the missing bottom sherd (which was uncovered in the 1997 field season). Another leg fragment was found in a concretion associated with the cauldron (57M16N2-22) and was successfully removed using the Cavitron and small chisel. The leg is straight with a partial ball (paw) or bulbous end. Like the pot, the metal of this leg is very mineralized under the surface, with a soft surface layer. Overall it is moderately magnetic.
Approximately 60 to 70 % of the concretions on and in the pot have now been removed. It is expected that the fish remains will only come out as separate bones (i.e. no large pieces). The fragile fragments of textile still remain attached to the bottom concretion. Removal of the remaining fragments of objects will continue with the Cavitron, small chisel or pneumatic tool. Once all of the interior material has been lifted out of the cauldron, the bottom concretion will be removed. If the legs are still present and attached, a support will be necessary as the remaining legs will not be able to support the weight of the pot. Due to the flexure of the pot along crack lines, it is anticipated that the cauldron will eventually have to be taken apart in many pieces and rebonded after treatment. Tests will be performed on a few small sherds to determine the best method of stabilizing the metal.
Douglas Beaton
conservator, Parks Canada
