Maintaining the surface or patina of sculptures and statues of bronze, marble, stone bronze, spelter or lead, whether kept indoors or outside, is very important.
Deciding where to place pieces is an important first step when thinking about conservation. Find a sheltered position but avoid places where water might drip, for example from a tree or a gutter, as this will stain a statue underneath and mould, algae and lichen form more readily on objects exposed to northerly weather. In extreme cold, stonework can split and shatter as moisture absorbed by stone expands on freezing. Removing soil from urns and troughs lessens the danger of frost damage, but wrapping an object against frost does not help as moisture becomes trapped. It helps to raise pieces above ground level on plinths with damp-proof membranes. Keep clear of fallen leaves and plants such as ivy as they can stain and secrete weak acids that may pit the surface.
Limestone, sandstone and Coade stone are comparatively soft and form a weathered surface crust which if removed will expose a vulnerable, crumbly surface beneath. They are affected by pollution which weakens the surface. Some stone dissolves or is irreparably worn away by misguided attempts at cleaning. If the surface is smooth and in good condition, it can be lightly hosed with water, easing loosened dirt with a soft-bristled brush. Algae and lichen do little harm and can add to the attractiveness of a piece of outdoor stone sculpture. It can, however, be removed, if the surface is sound, by brushing with a solution of a teaspoon of dichlorophen to a pint (570 ml) of water.
MARBLE AND ALABASTER
Marble is porous and discolours easily, particularly in salt or polluted air, and it can be stained by rust, algae and lichen as well as smoke from fires and oil. It is also prone to cracks, chips and breaks. When handling white marble, clean hands are essential. Marble objects will deteriorate much more quickly if displayed outside and even inside they can be damaged by damp, particularly if they are white. Avoid putting them in bathrooms, near open windows, indoor swimming pools or in conservatories and do not spray house plants if they are standing on or near marble as the fine mist may eventually cause the marble to stain. Coffee can permanently stain marble so avoid putting coffee cups on the shelf of a marble fireplace. Do not display marble above fireplaces, radiators and other heat sources as the rising heat will deposit dirt on the surface. When moving marble table tops, carry them vertically, not flat, as they can crack or split very easily.
Never clean ancient, rare or precious marble pieces or marble that has a deteriorating surface. Always ask for professional advice and be aware that attempts to move stains from porous stone may force the stain deeper or erode the surface. Indoors, do not allow marble to become very dirty but never use dusters, particularly coloured ones, as they tend to rub the dust into the surface and may smear greasy dirt. Feather dusters are also best avoided as any broken ends can scratch the surface. Remove dust with a dry artist’s white hogshair paint brush. It is best not to wash marble but if it is very dirty and in sound condition you can clean it by wiping the surface with swabs of cotton wool dampened with a mixture made up of half a pint (300ml) white spirit, half a pint distilled or deionised water and one teaspoon of a non-ionic detergent.The mixture can be kept in a screw-top jar (not metal) and used when necessary having shaken the mixture well before use. Wipe the damp swabs in one direction only and do not rub the surface. Discard as soon as they become dirty and work from the bottom upwards to avoid any cleaning fluid running down on to a still dirty area where it will ‘set’ the dirt and make it almost impossible to remove. The swabs should not be so wet as to allow the fluid to run. Clean a small area at a time and rinse as you go by wiping with clean swabs of cotton wool dampened with distilled or de-ionised water. Use dampened cotton buds on small objects or intricate carvings, again discarding them as soon as they become dirty. A specialist poultice is used in marble workshops to draw stains out so any badly marked marble is best left to the professional.
Marble fireplaces are usually waxed to seal and protect them against dirt but the wax will wear away over time. They can be dusted using the brush attachment of a vacuum cleaner but be very careful not to knock the marble which will scratch it. After cleaning a marble fireplace, as described above, it can be re-sealed with a very little microcrystalline wax and this allows it to be occasionally wiped with a damp cloth. However waxing will accentuate any existing stains so if stains remain after cleaning it is best to leave the fireplace unwaxed. Alabaster, soapstone and onyx are all porous and much softer than marble so can easily scratch or break. Objects made from these materials should never be immersed in water or displayed outside or in a damp room. Remove dust before cleaning otherwise the dirt will be absorbed. Pieces can be cleaned with the same white spirit and water mixture used for marble, using just dampened cotton wool swabs so as not to wet the surface then rinse off with swabs of cotton wool dampened with white spirit. Dry with a paper towel or soft, clean white cloth. To enliven a dull surface, a little microcrystalline wax can be applied and then gently buffed. If alabaster urns are used as lamps, always use a low wattage bulb as too much heat will cause the alabaster to deteriorate.
BRONZE, SPELTER AND LEAD
A desirable patina forms on bronze, often dark or greenish brown, and this must be preserved so only dust and never use metal polish or solvent on any bronze, or even water on bronzes kept indoors. You can, however, occasionally apply a little beeswax polish, with no solvent in it, with a soft cloth to help protect the patination. Spelter is softer and more brittle than bronze and is prone to corrosion. Figures are often thinly cast and fragile so should be held at the most solid part. Painted or gilded figures should never get wet but be lightly dusted with a soft-haired artist’s brush. Lead is heavy and very soft so is easily dented and scratched. It is also poisonous so always wash your hands after handling it. Dust indoor lead frequently to avoid any white, powdery corrosion. A sound surface can be cleaned with a softbristled brush or cotton wool dampened in water with a few drops of non-ionic detergent. Rinse and dry well. Unpainted pieces made from all these materials can be protected with a light coating of microcrystalline wax and then gently buffed with a soft cloth. Any serious corrosion or damage should only be treated by a professional conservator.
Plaster is extremely soft, porous and water-soluble so should never be washed and only ever be gently dusted with a soft-bristled brush – dusters will rub the dust into the surface and may smear greasy dirt. Try to protect plaster objects from dust, avoiding placing them near a source of direct heat as the heat will carry dirt upwards and deposit it on the object. Avoid damp areas such as bathrooms and conservatories and do not place painted pieces in direct sunlight. When handling plaster objects always have clean hands and take great care as plaster will chip and break very easily.