Updated: Jun 18, 2022
Stone sculptures, indoor and outdoor sculptures, can be found everywhere around us. These could be temple deities, family worship idols, miniatures in marble, lions and birds standing on gate pillars and stone carved outdoor exhibits that find way in our gardens and balconies. Stones such as soapstone, alabaster, sandstone, limestone, marble, basalt and granite have been used in sculptures. Stone sculptures can boast of best longevity and easy-care options amongst all heritage objects and this could involve simple cleaning. However, as any material, stones also undergo natural weathering and deterioration with time. Stability induced by good house-keeping practices, proper display and storage can be key to ensure that they are passed on to future generations in pristine conditions. Caring for sculptures is easy once we know the material, the signs of deterioration and ways of preventive care.
What are Sculptures? What is the history / origin of stone sculptures?
Sculptures are three dimensional objects made of stone that may be carved out or assembled by joining more than one piece. Stone being a durable material, several stone sculptures have survived over the years in various parts of the world.
Petroglyphs or rock engraving on cave walls were perhaps the earliest form of carvings in stone. The Löwenmensch figurine and the Venus of Hohle Fels in Germany, are considered the oldest statues in the world. The oldest known life-sized statue is Urfa Man found in Turkey.
What stones are used in sculptures?
The combination of the natural colour, grain, texture of the stone and the man-made carving creates the unique stone sculpture art. A range of stones with varied textures have been used with great advantage for carving sculptures.
Common stones used are soapstone, alabaster, red sandstone, limestone, white marble, basalt and black granite. Many other stones have also been used depending on geography, availability and cost. The selection of stone for sculpture is based on softness/hardness, availability and the colour, texture or finish.
How to identify stones used in stone sculptures?
The main classification of stone in nature is based on its origin/formation and according to this there are three main types of stones- igneous, sedimentary and metamorphic.
Igneous stones are tough, cooled lava melts with little texture or layering. Rocks like these contain mostly black, white and/or gray minerals. These include granite, diorite, basalt, and obsidian. These are some of the hardest stones used for sculpture.
Sedimentary stones such as limestone, sandstone or shale are hardened sediments carried in rivers and deposited in lakes and oceans. With time, the sediments lose water and become cemented under temperature and pressure to form rock with a distinct layer (strata) or beddings. They are usually brown to grey in colour and may have fossils and water or wind marks. Many varieties of sandstone and limestone, which vary greatly in quality and suitability for carving, are used for sculpture.
Metamorphic stones are formed when a sedimentary rock or igneous rock is exposed to heat and pressure and undergoes a chemical change which forms a new crystalline material. The most well-known metamorphic rocks used in sculpture are the marbles, which are recrystallized limestones.
The colours and textures of stone can also be useful properties for identifying stones. As complex mineral forms, stones are also richly variegated in colour by the irregular veining that runs through them.
Marble stones are fine-grained with colours ranging from pristine white to blue/grey, pink and black and can be carved with delicate detail and finished with a high polish. Marble also has a translucent quality, that is the stone seems to glow as it responds to light.
The granites may be predominantly black or white or a variation of greys, pinks, and reds. They do not have uniform colouring, but a more salt-and-pepper quality and it may glint because of mica and quartz crystals in it.
Sandstones vary in texture and are often more warm- coloured in a range of buffs, pinks, yellows and reds.
Limestones, although whitish, may vary greatly in colour, and the presence of fossils may add a different texture to their surfaces.
What can go wrong with a stone sculpture and why?
Although stone is generally considered to be a hard material, it is subject to decay and weathering. Cracks, pitting of surface, change in colour, depositions are all signs of decay. Deterioration in stone depends on the nature of the stone and its location (indoor or outdoor).
Weather erosion, the effect of air pollutants, salt crystallisation, biodeterioration, repeated wetting/drying cycles, unscientific previous restoration (use of strong adhesives, cement), improper display and storage, vandalism, accidents can all lead to damage to stones. Painted and gilded sculptures should not be exposed to light for a prolonged period.
Observation, regular monitoring and vigilance and timely recognition of decay can help to prevent damage to stone.
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Why are there cracks in my stone sculpture?
Cracks in stone sculptures are rare.
However, cracks in stone indicate use of poor-quality stone, bedding planes in the wrong direction or settlement (mostly in sedimentary rocks), corrosion and expansion of metallic dowels used for fixing.
In outdoor sculptures or stones exposed to weather changes, the cracks may be due to rain and snow (dampness) which may penetrate the surface and create trapped moisture, destroying the internal stability or extreme fluctuations in day and night temperatures. Formation of soluble salts within the stone and their crystallization may also lead to cracks.
It is important to consult a conservator in case cracks or powdery or friable stone surface are visible.
What can I do to prevent cracks in stone sculptures?
Cracks formed due to inherent defects in the stones are not something one can predict or prevent from happening. Also, natural weathering of stone is inevitable, especially stones that are exposed to environment. Some stones such as granite are more resistant to weathering than others such as limestones or sandstones.
There are three major causes for cracks in stones; pollutants that are source of acids and soluble salts, frost or sudden change in temperatures and crystallisation of soluble salts. Water penetration is the main catalyst and the ability to resist damage or cracks depends on the nature of stone structure.
However, following simple steps one can prevent cracks in stone.
Avoid exposure to water/moisture: Do not display stones on or near damp surfaces (walls or ground).
Ensure that the stone surface is clean and dry and not in a polluted environment.
Avoid frequent wet cleaning. Water trapped in stone may lead to internal stress and cracks.
Should I clean stone sculpture at home?
Surface dirt on a stone is not usually a problem except from an aesthetic view.
Many carved stones suffer from the accumulation of a black crust on the sheltered undersides of the carving; this may lead to decay in the future but can also be completely stable and protective. Some retain it as it helps the definition of the carving by accentuating the shadows.
Cleaning of Stone Sculpture - Subrata Sen
Moss and lichen grow readily on exposed stone and do not usually cause decay except through water retention and the subsequent action of frost and salt. Hence need to be cleaned. Although some might argue that such growths contribute to the patina of the object.
The surfaces of carved stones should therefore not be cleaned very frequently, especially wet cleaning, as the action of cleaning can cause accelerated deterioration (especially to sandstones) or re-soiling by opening the pores of the stone.
Any cleaning is best carried out without using water. It is best to use gentle, dry, soft brush to clean stone surface.
If the stone does require a washing, use water with delicate spray, preferable de-ionized or filtered water and no detergents. Also, ensure that the stone is dried completely after cleaning using a cloth or air-dry.
Frequency of wet cleaning of a sculpture depends on its exposure to pollutants and the type of surface depositions build-up. In case of hard, stubborn deposition on the stone surface, it is better to consult a conservator.
Should I apply protective coatings on sculptures?
Avoid applying protective coatings and commercial products that contain oils, waxes or acrylic resins on stone surfaces. These will change colour and degrade over time. Also, in some stones they block the natural pores in stones and create more problems. Water-repellent coatings have the potential to trap water. In the longer term, these coatings may cause surface pitting and spalling.
What is the best way to move sculptures?
The main problems associated with handling or moving of stone objects include scratching the surface of highly polished or soft stones (talc, soapstone, marble), the absorption of grease, dirt, oil and salts from hands by porous stones (marble, alabaster, limestone) and accidents and breakage when carelessly handling or moving objects. To minimize the risk of damage:
Avoid unnecessary handling or moving sculptures as most damage is done to objects through poor handling. While moving remove jewellery, particularly on hands and wrists, as it can scratch surfaces and ensure your hands are clean or well-fitting disposable or washable gloves.
Handle only one object at a time and assess the condition of your sculpture before handling it. Check the attachment between an object and its pedestal or base before moving. Use flat, thick, and soft padded supports to carry it if it is fragile or unable to support its own weight. Pick it using both hands cradling the strongest points; do not lift it with handles or other protruding parts.
Assess the weight of the sculpture to be handled. If an object is too heavy for one person, use more manpower or use a trolley. Do not drag or push it across a surface.
What are the best ideas for displaying my sculpture?
Indoor sculptures (inside the homes) should be generally displayed at eye level for optimal viewing. Flat surfaces such as tables, recessed spaces in walls or within a bookcase are all ideal spots for display at home. The location of display should be areas that are dry (no dampness), and not too hot (near fireplace or radiator) or too cold.
Marble or limestone sculptures should not be exposed to high temperatures, direct heating from strong lights, sunlight, radiators, etc within the home environment.
Sometimes, it is better to put sculptures in display cases to prevent dust accumulation or exposure to pollution. Statues and sculptures come in many shapes and sizes, and in many cases, display pedestals or clear acrylic display cases for them should be custom made to order.
The pedestals are useful for indoor sculptures as they prevent the direct contact with floor surface and changes of dampness. These should be visually appealing yet should not compete for attention with the sculpture itself. The pedestals and cases must also be designed to the weight of the object, as well as its size. Non-corrosive metals such as steel may be used for locking sculptures for display.
Outdoor sculptures: Avoid iron and copper-based locking clamps while displaying outdoor sculptures and do not embed them in concrete. Displaying an outdoor sculpture under partial shelter may help to avoid the issues caused by exposure to rainfall, as well as providing shade from direct sunlight.
How do I store my sculpture?
The aim of storage is mainly to ensure that objects are protected against the agents of decay such as inappropriate temperature and relative humidity conditions, exposure to light, biological agents, dust, and pollutants and accidents.
When storing stone objects consider the following guidelines:
Store small, lightweight objects in acid-free cardboard boxes that have a rigid base, place padding under and around objects.
Clean cotton wool, acid-free tissue or polyethylene bubble wrap are suitable for padding.
Place large, heavier objects in closed cupboards or cover them if on open shelves to avoid dust accumulation.
Place the largest objects on the lowest shelves and keep shelving at a safe height.
How do I look after my outdoor stone sculpture?
Sculpture displayed outdoors or in open spaces are all considered as outdoor sculpture. These can be deities in front or gardens, animals such as elephants, lions figurines in the front, garden statues, rock garden features in stone, fountains or public art.
It is advisable to do regular inspection, cleaning, and maintenance to keep sculptures free of fungal growth, biological growth, pollutant build-up or dust and dirt.
It is important to maintain garden around the sculpture to ensure that there is no overgrowth of plants, weeds, or roots which may disturb the base of sculptures.
Wet cleaning, if required should be undertaken in warmer temperatures to ensure complete drying up of moisture from the sculpture.
Covering your statue for prolonged wet and cold seasons is the simplest way to prevent deterioration. If possible, removing and relocating the statue to a clean and dry storage location for these seasons is advisable.
Putting a sculpture under partial shelter may help to avoid exposure to rainfall, as well as providing shade from direct sunlight.