Excavations in the Abbey River, directed by Edmond O'Donovan, for the Limerick Main Drainage works have returned a rich cache of finds. The site has almost exclusively produced nonorganic items, and the conservation has so far focussed on the metals, both ferrous and nonferrous. Nine hundred and sixty-five objects, including 46 leather artefacts, 12 wooden artefacts, 278 coins and 629 miscellaneous metal pieces, have been received by ArchCon to date.
The objects are often covered with thick layers of corrosion and riverine concretions, obscuring their shape and surface detail. The ferrous artefacts also undergo active corrosion after excavation, due to high chloride levels in the river. After X-raying and documentation, the objects are cleaned mechanically using a variety of hand tools. In some instances, mild acid treatments are adopted to loosen the calcareous riverine deposits. Different acid solutions are used depending on whether the metal is silver or a copper alloy. With iron items, a micro air-abrasive technique is used to complement the mechanical cleaning: using a compressed air system, the operator directs a stream of tiny particles of aluminium oxide at the object, varying the flow and strength of the particle jet as appropriate. Storage in a dry environment should prevent corrosion continuing on the iron. However, chemical washing in a weak alkaline solution can aid this process by removing the chloride ions that cause the problem. Iron items displaying signs of active corrosion are therefore treated with this method when cleaning is complete.
The leather items recovered from the Abbey River were in a fragmentary condition. After cleaning and documentation, these artefacts were soaked in a solution of glycerol to help lubricate the leather and prevent dimensional change when dried, by freeze-drying in this case. With this method, the objects are dried from frozen, greatly reducing the shrinkage and warping that occurs during normal 'air-drying.' A similar approach was taken for the 12 wooden items, which were soaked in a solution of polyethylene glycol (a synthetic wax), before being freeze-dried. Currently, objects from this excavation are being conserved for inclusion in an exhibition to be held in Limerick later this year.
Objects of interest Mortar bomb 98E581:1581 This complete mortar bomb consists of a cast-iron sphere with central cavity for holding the explosive (black powder). There is one fuse hole, which is 40mm deep (thickness of the iron cast) and 27mm in diameter. The cavity has a volume of approximately 5.6 litres. The bomb was found under Baal's Bridge, and it is believed to have been part of the arsenal of William of Orange, who led a failed siege on Limerick in 1690 and is known to have attacked this particular bridge.
After excavation, the fuse hole was unblocked by army bomb disposal experts and declared safe. Despite the date of the bomb, if the explosive had remained uncontaminated and dry, it could still have ignited. The contents of the cavity were removed for analysis prior to conservation efforts. Before conservation, the bomb was soiled and had some concretions on the exterior. There was active corrosion occurring, with large droplets of iron chloride forming at several points. The object is extremely heavy, with three people being required to lift it comfortably. This size and weight have restricted the choice of treatments.
The bomb was recorded with photography, drawings, and X-radiography. It was too large for one X-ray plate, so several were taken in an effort to map the construction detail. The analysis revealed that the sphere had been made in two parts and that there was a ridge on the interior where the hemispheres joined.
Cleaning began with the removal of the larger concretions using hand tools, followed by washing with water to remove the loose soiling. The interior cavity was filled with water and rinsed out several times. The object was then soaked in a weak alkaline solution in an attempt to remove free chloride ions. After an extended soaking period, the bomb was removed, rinsed repeatedly and then air-dried.
The artefact should now be maintained in an environment where the relative humidity is less than 15% in order to prevent corrosion occurring.
Bronze pocket sundial 98E581:1549
This is a delicate circular-shaped object, 34mm in diameter and only 2mm thick. It consists of a flat outer ring, across the inside of which a Y shape extends. On the leg of this Y, there is a flip-up wedge used for casting a shadow. Numbers from 4 to 12 and from12 to 8 run three quarters of the way around the circumference.
On arrival for conservation, the surface and much of the shape of the object was obscured by heavy calcareous concretions. The object was photographed and X-rayed as part of the recording process. The X-ray revealed that a pin was embedded in the surface concretions.
The sundial was cleaned using hand tools, under a microscope. Some of the concretions were very stubborn and were removed using a mild acid and thiourea solution. After cleaning, the shadow arm could be moved again, and the numbers could be clearly seen.
The cleaned object should be maintained in an environment where the relative humidity is less than15%.
ferrous and nonferrous. Nine hundred and sixty-five objects, including 46 leather artefacts, 12 wooden artefacts, 278 coins and 629 miscellaneous metal pieces, have been received by ArchCon to date.
This complete mortar bomb consists of a cast-iron sphere with central cavity for holding the explosive (black powder). There is one fuse hole, which is 40mm deep (thickness of the iron cast) and 27mm in diameter. The cavity has a volume of approximately 5.6 litres. The bomb was found under Baal's Bridge, and it is believed to have been part of the arsenal of William of Orange, who led a failed siege on Limerick in 1690 and is known to have attacked this particular bridge.
On the leg of this Y, there is a flip-up wedge used for casting a shadow. Numbers from 4 to 12 and from12 to 8 run three quarters of the way around the circumference. 
On arrival for conservation, the surface and much of the shape of the object was obscured by heavy calcareous concretions. The object was photographed and X-rayed as part of the recording process. The X-ray revealed that a pin was embedded in the surface concretions.