We actively promote good practice in the care of lead sculpture, and to this end we have produced three additional information pages which we hope may be helpful to those responsible for the care of lead sculpture, to students and to practitioners. Below are explained and illustrated some of the more typical forms of damage and deterioration found in lead sculpture.
Expansion of the iron armature:
The production of lead sculpture reached its height during the 18th century. Lead sculpture was most commonly made by casting, using processes very similar to those employed for bronze, producing a hollow cast with a thin outer shell. However, lead being a heavy and soft material it frequently required additional support when used to make sculpture.
This was in part provided by the core and the iron armatures that were left in the castings or by additional supports, usually wrought-iron, built into the casting after manufacture, large garden urns being an example of this.
The primary reason for structural failure of lead sculpture is the corrosion of the wrought-iron armatures and fixings within the casting. If water enters the casting and the porous core material becomes wet, the iron corrodes. Rust can occupy up to ten times the volume of the pure metal, for instance 1mm of iron when rusted can convert to 10mm of rust. This results in huge expansion pressures being exerted on the lead casting which after some time will split, allowing more water to enter and accelerate the decay. The image above left shows the rusted iron armature and core material inside the leg of a lead sculpture, after cutting an access panel to allow removal and replacement of the iron armature.
By consequence there is also a weakening of the armature or fixing which, if the sculpture is fixed to a stone plinth, can cause fracturing of the stone by the pressure of rust jacking and result in instability. If red rust staining is visible on or around the base of lead sculpture this would indicate that there is a potential problem with the internal iron armature. The image left shows splitting of the same leg before removal for conservation - the expansion having also split the stone.
Casting faults: Dross
The casting process itself can also contribute a number of problems that can develop into structural failure. When melting lead for the purpose of casting, impurities in the metal float to the surface of the crucible as they are freed by stirring the molten metal, and these should then be scraped off. If the metal is poured into the mould without this cleaning process being thoroughly done, then the material known as ‘dross’ will be incorporated into the casting and form weak, porous areas which can fracture or become sites that can initiate corrosion at a later date.
The image on the left shows dross (the red-brown material) causing major fractures in a lead sculpture.
Casting faults: Cold pour
The temperature of the metal at pouring is also critical; if too hot it will boil and if too cold there is a chance of it starting to solidify before flowing fully throughout the mould. If this occurs, chilling metal can meet as the metal fills the mould and will not properly combine before solidifying, resulting in areas of structural weakness often referred to as a 'cold shut', pictured left.
Poorly fired moulds or damp core material can also cause the release of gas or water vapour as the casting takes place, resulting in areas of porous, weak metal filled with fine holes as the gas is trapped as the metal solidifies. The image left shows cold pour that has caused structural weakness resulting in fractures.
Casting faults: Inclusions
Additionally if the core or outer investment of the mould are not prepared well, particles of lime, sand or plaster can be washed into the molten metal as it is poured into the mould. These non-metallic inclusions will produce weak areas in a similar way to the dross previously mentioned.
The image left shows inclusions in the foot of a lead figure sculpture.
Lead’s inherent softness as a material and its scrap value has long made it a target for thieves. Any sculpture and garden ornament sited outdoors should be security fixed. Though the sculpture could still be damaged in attempted theft, a well-designed security fixing should delay and deter the thieves from being able to actually steal the object.
The image left shows fractures in the ankles caused by thieves attempting to wrench the sculpture off its plinth. The stainless steel securty fixings held fast, preventing the loss of the sculpture.
Again, lead’s softness makes it vulnerable to severe damage from heavy impact, caused perhaps by vehicle accident or falling trees (as pictured left, where a fallen tree has severely impacted the back of the female figure's head and neck).
This should of course be borne in mind when siting sculpture or planning planting close to it.
Missing parts and attributes:
Usually as a result of general wear and tear, lack of maintenance or theft/vandalism, sculptures are often found with missing parts. Replacement of these should only be considered where reliable historical evidence can be found upon which to base the replacement. For example, if the sculpture has a missing hand, it may be possible to find another contemporary cast from the same workshop and gain the owner's permission to take a mould of the hand and recast it in lead. Recasting in fibreglass or other inappropriate materials should not be permitted, except perhaps in the exceptional circumstance of persistent theft.
The replacement of missing attributes is a more complex problem, because reliable evidence may not be so easily found and comparison with existing attributes on the same sculptures found elsewhere may be later replacements, which in themselves may be inaccurate.
The photo left shows a lead figure of Diana, missing her attributes of arrow, quiver and bow, below left shows the same sculpture after the replacement of her missing attributes.
The ethics of the replacement of attributes are subject to debate and each decision should be made individually. Our general view is that the replacement of attributes is highly important in order to enable the aesthetic and narrative aspects of the sculpture to be understood by the viewer as per the artist's original intention. This is particularly pertinent to classical or allegorical subjects and when, for example, a figure is holding an object in their hand - with the object present, the subject identifies itself and indicates its character and the associated allegorical significance of the subject - and the pose makes sense; without it, the figure may be only making a meaningless and confusing gesture.
Care must also be taken to select the correct attribute to replace. It is known that John Cheere and perhaps also the other well-known eighteenth-century lead sculpture workshops occasionally re-used the same figures for different classical subjects, distinguishing one subject from another partly by the aid of attributes.
If missing parts or attributes are replaced, detailed records and photographs must be provided to the owner so that the date and extent of the replacement is known in the future.
Vandalism and abuse:
As a soft material, lead is very vulnerable to vandalism. Superficial dents and scratches to the surface are often found on sculptures accessible by the public.
Over the years we have also inspected many leads which have been repeatedly damaged by the impact of shot gun pellets (shown on the lioness’ neck, far left, alongside scratched graffiti).
Squirrels are partial to lead and frequently gnaw at it for extended periods of time, causing disfiguring damage, as can be seen along the edge of a sculpture base, photo left.
Lead is attacked by organic acids produced by algae (pictured left), lichen and mosses, which can pit the surface of the lead. Algae on lead sculpture should be removed by gentle washing, at least annually.
Lime based materials such as cement and mortar in the presence of moisture can initiate corrosion if free lime is in contact with the metal.
Other acids such as hydrochloric or hydrofluoric will rapidly attack lead; these acids are used in some masonry cleaning products.
Also acetic acid and other organic acids will corrode lead. A large number of timbers contain these organic acids.
Lead dioxide formation:
Over the past fifteen years in the United Kingdom we have observed a growing incidence of outdoor lead sculpture and other lead constructed items, such as roofs and rainwater goods, developing a visually disfiguring, red-brown to purple-brown surface discolouration. The photo left illustrates a severe case of this.
For further details and an explanation of this problem click here.
We hope the above information is helpful. Please do not hesitate to contact us for further advice