ADDITIONAL INFORMATION: POOR TECHNIQUES TO BE AVOIDED WHEN CONSERVING LEAD SCULPTURE
We try to actively promote good practice in the care of lead sculpture and we hope that our lead sculpture example pages on this site demonstrate our recommended techniques. By way of guidance and cautionary advice to owners of lead sculpture commissioning conservation or repair works, this page is designed as an outline of techniques that, in our view, should not be permitted - either because they are deemed ethically unsound or practically unfit.
Historically, repairs to lead sculpture were carried out in situ, usually by unskilled estate staff employing techniques ranging from a reasonable use of what was available at the time, to the downright bizarre. However, these efforts often did save many sculptures from being scrapped. Because even poor past repairs have some historic value in themselves, we only remove them where they are damaging, structurally incapable or visually disruptive, but this decision has to be balanced by taking into account the context of the piece and the level of intervention required to remove the old repair.
Over the last 28 years we have encountered many examples of the results of poor techniques, either centuries old or, sadly, recently employed. Today there is no excuse for the use of ineffective techniques or unethical practice. Only qualified and experienced conservators with a proven track record in the ethical conservation of historic lead sculpture should be commissioned to carry out conservation or repair works. It is very important that conservators working on lead sculpture and objects are knowledgeable in the history and techniques used to produce and decorate this material.
Please scroll down for illustrated examples of poor techniques to avoid:
Soldered or wiped repairs
Before the introduction of gas welding in the mid-nineteenth century, repairs were carried out using fire-heated soldering irons or wiped joints using molten lead (a plumbing technique). This type of repair was often structurally unsatisfactory and in most cases failed. Also, solder alloys do not achieve the same patination colour as the surrounding original lead surface, so those repairs are visually unsympathetic.
The hindquarters of this eighteenth-century lead horse displays a variety of unsightly old repairs, using various techniques and dating from various periods.
Inappropriate repair materials
Cement, concrete and putty were often used to fill holes and support the structure of failing lead objects.
Scrap reinforcements
In the past, ad-hoc pieces of scrap metal were used in an attempt to strengthen or support failing structures.
We often find old railings, pipe (pictured left), fire irons or machinery parts and even animal bones placed inside severely damaged sculpture.
Iron, steel or copper used in this context will eventually fail but many of these reinforcements saved some sculptures from collapse for many years.
Props
We have also often inspected collapsing lead sculptures that have been propped up by scaffold poles or similar struts.
This can be a useful stopgap to temporarily prevent the sculpture from falling over, but a conservator should be brought in as soon as leaning or impending collapse is observed.
Failure to act quickly could result in catastrophic damage to the sculpture and / or severe injury to people.
Expanded foam
Over the past twenty-five years, some conservators have, after the repair of a lead sculpture, employed the technique of replacing the original core with a variety of expanded foam materials. The most common foams used are pourable, two-component, semi rigid, closed cell polyurethanes developed in particular for the building and marine industries for insulation and buoyancy respectively.
The foam is introduced into the sculpture by pouring or injection under pressure through purpose-made holes in the lead, after a new armature has been installed and the repair is complete.
The reasoning behind the use of these materials is that the foam replaces the structural support to the lead previously provided by the original hard refractory core, and being closed cell prevents water ingress into the sculpture; in addition it helps set and hold the new stainless steel armature in place.
Unfortunately there are a number of significant problems with the use of closed cell polyurethane foams that make the material unsuitable for the conservation of lead sculpture. These are detailed below:
1. These high performance foams have only been in use for just over 30 years and although they are quoted in building literature to have a life span of up to 50+ years, there is little data available to support this.
2. Polyurethane polymer is a combustible solid and can be ignited if exposed to an open flame. Decomposition from fire produces mainly carbon monoxide, and trace nitrogen oxides but critically hydrogen cyanide, as one of the components of the foam is methylene diphenyl diisocyanate. The fact that the foam is combustible means that no future lead burning repair work is possible without the removal of the foam from the sculpture.
3. Due to the combustibility of the foams, the holes used to pour the catalysed foam into the sculpture have to be filled and sealed with a synthetic filler rather than be lead welded, these filled holes then have to be disguised.
4. Polyurethane is resistant to most chemicals, particularly hydrocarbons and solvents, therefore removal has to be by physical means, on a complex sculpture this usually means cutting the sculpture up, opening large windows through which the foam can be extracted. The task is made more difficult by the rough inner surfaces of the casting to which the foam strongly adheres.
5. Closed cell polyurethane foams have a typical density of between 35kg/m³ and 60kg/m³. The compressive, tensile, shear characteristics of rigid polyurethane foam are primarily a function of its density with strength behaviour varying considerably within the range of 120 and 450kPa (kilopascals). This performance is not nearly sufficient to prevent a lead sculpture moving under its own weight if not already adequately supported by a well-designed armature, nor will the foam minimise accidental impact damage. The misguided assumption that rigid foams have the necessary structural ability to assist in supporting a sculpture has lead to the installation of inadequately designed and incorrectly installed armatures.
6. Poured closed cell foams have a 90% to 95% closed cell formation therefore they are not totally impermeable to water nor water vapour. With foam being used to fill the sculpture there is the possibility of the formation of interstitial condensation between the foam and the lead. In contact with pure water in the form of condensation, a non-protective lead corrosion product white lead oxide can form instead of the far more resilient surface film of lead carbonate and lead sulphate naturally formed on the surface of lead. This can be exacerbated by the presence of certain acids. As cast lead sculpture contains many casting flaws, areas of gas porosity and inclusions of dross, the potential of establishing sites for corrosion to initiate and water entrapment is high if water is unable to escape once it has entered the sculpture.
Taking the above factors into account it is evident that the introduction of a non-reversible material such as closed cell polyurethane foams that severely complicates future repair goes against conservation best practice, unless there is a strong extenuating case so to do. Conservation work undertaken to lead sculpture should be executed with the intention that the sculptures will remain in sound condition for their foreseeable lifetime measured in hundreds of years, not tens.
Poor armatures
Sculptures needing major conservation work due to the failure of the iron armature and general structural collapse generally require a new armature to be constructed using 316 grade stainless steel. This will necessitate careful opening up to remove the original core and rusted iron.
If properly designed and fitted (unlike the bar in the arm, pictured left), a new stainless steel armature will be all the sculpture requires to retain its form, so any foam, synthetic fillers or reinforced glass fibre resin to give additional support is unnecessary and inappropriate unless there are exceptional circumstances (see above).
The new armature must be very carefully designed and installed correctly to ensure it is structurally capable and functions effectively (pictured left).
Inspection of the armature is not possible after the conservation is completed, so the work must be undertaken by competent craftsmen who should photograph it for the client as it
progresses.
Polyester fillers
The filling of non-structural holes, cracks and faults in the casting surface using hard polyester fillers is not considered ethical except in exceptional circumstances where access to enable lead welding repairs is not possible.
We have come across many examples where such fillers, not even colour-matched to the lead (pictured left), have been used because the lead was intended to be fully repainted.
This completely relies upon the paint surface being maintained in order to conceal the unethical repairs and moreover is an unnecessary use of a modern and incompatible material.
Aggressive cleaning techniques
The abrasive cleaning of lead (whether using air abrading or hand methods with wire brushes, abrasive papers and pads) should be avoided in all but the most exceptional circumstances, for two main reasons: Firstly, this irreparably damages the surface, both pitting the lead and destroying fine tooling and modelling.
Secondly, abrasive cleaning also removes all traces of original paint coatings which are highly significant and should be sampled and analysed as part of any conservation work (more detail below).
In addition, abrasive cleaning removes naturally formed patina which is unnecessary as lead generally forms stable corrosion products which if removed are impossible to recreate artificially. Abrasively cleaned surfaces also leave the sculpture looking flat and characterless (example pictured left).
Unfortunately there are many examples of lead sculptures and decorative objects having been cleaned with air abrasives in the past thirty years.
Once lost, the cast and tooled surface of a casting (as shown in the detail, left) cannot be regained. When necessity requires cutting into a sculpture, the location of these cuts must be positioned where minimal damage is caused to the decoration.
In the conservation of complex, detailed leads the conservator should rework and chase any damaged detail caused in the repair process using the correct hand tools, which may need to be specially made in some instances.
The photo left shows an example of finely-tooled surface of lead sculpture which is lost if abrasive cleaning is used.
Loss of original paint
Evidence suggests that most lead sculpture and decoration was originally painted to simulate stone or bronze. Therefore before even gentle cleaning of a lead sculpture takes place, evidence of original paint (pictured left) should be carefully looked for and samples taken for analysis, and then any such traces of paint should be left undisturbed by the conservation process as far as possible.
The significance of taking and analysing paint samples cannot be overestimated as this provides vital historic information on the decoration of sculpture, much of which has already been lost forever by the use of aggressive cleaning techniques.
Although lead sculpture is generally seen today in its natural unpainted form, this is only due to the gradual degradation of the original paint or inappropriate cleaning. However, enough paint will still exist in recessed areas on many sculptures to allow samples to be taken and analysed.
Analysis of the sample pictured left, illustrates a cross section of 19 successive layers of paint on a lead urn, applied over two centuries.
Poor decisions regarding surface finishes
Whether to reapply paint to the surface as would have been originally done is a complex question. A curatorial decision to repaint lead sculpture should not be taken without sound historic evidence, including paint analysis.
In recent years, painting has sometimes been used inappropriately, in many instances to disguise poor or otherwise disfiguring repairs or to hide the use of synthetic filler.
Leads have even been painted grey in an attempt to simulate natural lead, resulting in a dull, flat surface (pictured left) that bears no relation to the original intention of the maker or the original finish the sculpture would have had.
The natural patina that lead accumulates after many years in the open air has now become a prized surface finish for many lead sculptures, retaining an aesthetic beauty of its own.
We do not remove the natural patina, though we may selectively remove intrusive stains if they interfere with the reading of the sculptural form.
Lead’s natural patina is protective in itself and (unlike bronze) it does not require wax or other protective coatings to prevent corrosion.
Basic maintenance involving annual light water washing to remove dirt, algae, lichen and airborne pollutants should be all that is required. This regime also provides an opportunity to carefully inspect for any damage or deterioration in condition, which should be swiftly attended to.
Repaired areas will be visible due to the lack of natural patina and their shinier surface (pictured left on the legs).
Our preferred practice is to disguise these areas with a thin wash of casein-based watercolour paints. As these paints slowly wear off in an outdoor environment, they are replaced by natural patina.
This technique negates any necessity to fully repaint in order just to disguise worked areas.
However, in recent years, a red/brown formation has been appearing on lead sculpture and architectural lead throughout Europe (pictured left).
The formation seems to develop on worked or new areas of lead that have lost or not had time to develop their protective, natural patina and our initial research indicates that it is caused by modern pollutants.
This has also necessitated the selective repainting of new or cleaned areas of sculpture in order to allow the surface time to rebuild its patina gradually as the paint degrades, thus preventing the development of the formation.
Our research into the cause and techniques of dealing with this is ongoing. (Click here for further details).
Poor storage or handling
Storage, and the lifting and moving of lead sculpture also require experience and care in order to provide the necessary support to avoid crushing or distorting the object (as pictured left, on a poorly stored sculpture).
A careful assessment of the sculpture’s structural condition and its likely weight must be carried out before attempting to lift the piece.
Like all conservation and repair works to lead sculpture, the lifting operation should only be carried out by qualified and experienced personnel.
Poor sculptural technique
A great deal of sculptural ability is required to repair sculpture. We have often seen past repairs carried out that distort the form, as with this Shepherd's right arm and hand.
We hope the above information is helpful. Please do not hesitate to contact us for further advice