Cleaning Marble Monuments

Angus Lawrence


  Garden statue with one half of face cleaned to show condition before and after treatment
  Eroded and soiled garden statuary marble, half of which has been cleaned using a controlled nebulous spray system

Marble has long been an important material for sculpture and monumental compositions, notably in religious settings. Whether related to a significant event or as a mark of remembrance, a monument will often become an important focal element in an architectural space.

As with all natural materials, marble is prone to varying degrees of soiling and deterioration which in turn can be detrimental to the appearance and appreciation of a piece, detracting from its significance as a work of art. Therefore cleaning aimed at refreshing or restoring a marble surface is often considered appropriate. As soiling may also hide evidence of deterioration, cleaning is often carried out as a precursor to conservation and repair work, in order to fully understand the condition of the piece. Cleaning, then, often forms a necessary and desirable part of a well-designed conservation specification. This should involve the simple removal of damaging or disfiguring deposits from the surface.

However, cleaning is an irreversible process and so the choice and application of the right materials and techniques are vital. Well-intentioned but damaging cleaning has sometimes been carried out in the past with the use of inappropriate processes, tools and materials.

Faced with an ever-expanding group of specialist marble cleaning products (in the form of powders, liquids, gels, pastes, etc) it is important to approach the cleaning of marble monuments with sound conservation principles and an awareness that a historic marble surface should be properly examined and assessed before any programme of cleaning.


Marble (from the Greek marmaros meaning a white, shining stone) is a metamorphic rock formed from limestone (CaCO₃) which has been broken down under pressure and heat to recrystallise and produce a granular mosaic of calcite crystals of roughly equal size. During this process, the original sedimentary elements of a limestone are lost and a pure marble is therefore monomineralic, free from fossils and white in colour. The vast range of coloured marbles is a consequence of small amounts of impurities being incorporated with the calcite during this metamorphism.

Marbles are found across the globe but the best known and most desirable come from Italy, Greece and Turkey. There are a handful of true British and Irish marbles, but they are relatively rare and most are only of geological interest. Most notable are the rocks from the Scottish islands of Iona, Skye and Tiree and Connemara Marble from the west coast of Ireland. Other stones that take a polish, such as Purbeck, are often called marbles but are in fact largely fossiliferous limestones, shale stones and other varieties.


Since indigenous marbles are both difficult to quarry and largely unsuitable for carving, marbles from abroad have been an important decorative and sculptural material in Britain since the Roman occupation. Although the architecture of ancient Rome is equated in the popular mind with the use of marble, the Roman buildings of Britain consisted mainly of timber, local building stones, and fired terracotta bricks and tiles, all cemented together with lime mortars and renders. Marble was, however, imported around the Roman Empire in the form of statuary, sculpture and monumental pieces to furnish temples, public buildings and private dwellings. Fine marble remains associated with the 3rd-century AD Temple of Mithras, which was excavated in 1954 in the City of London, are on display in the Museum of London.

  Marble cartouche with heraldic design before and after cleaning  
  A finely decorated marble cartouche on a monument from the 1780s, before and after cleaning to remove dust, decorators paint and surface soiling. The monument had been divided in two by a stud wall, hence the vertical paint marks. The solvents used included acetone, saliva and deionised water.  

The use of marble tesserae in mosaic flooring is also well recorded and in the Middle Ages Italian craftsmen imported material from archaeological remains in Italy to reuse with indigenous stones in order to achieve the decorative patterns and colour combinations of the Cosmati pavements at Westminster Abbey and Canterbury Cathedral (both 13th century).

Alabaster was the main stone used for religious sculptures and monuments in Britain from the mid 14th century. A vibrant and profitable industry grew up in London, Nottingham, York and Burton upon Trent and mass-produced sculptures based on stock themes and imagery were exported in large numbers to mainland Europe. Sometimes mistakenly identified and referred to as marble, alabaster is geologically very different, being a form of gypsum – hydrated calcium sulphate.

The 17th century saw the eventual replacement of alabaster with marble as the main material for church and other monuments. Sculptural and architectural styles based on European examples were studied, copied and then developed in Britain and the demand for marbles increased as monuments became more exuberant and ambitious in breaking free of the staid conventions of the alabaster workshops. A typical example of this development can be seen at St Mary’s, Bottesford in Leicestershire, where the use of alabaster for the fine memorials to the Dukes of Rutland was phased out in the middle of the 17th century in favour of statuary marble.

Realistic portraiture became a key component of many monumental compositions with the finest statuary marble being sought out to produce sculpture of the very highest quality. Marble funerary monuments were important commissions for the top sculptors and carvers during the late 17th century through to the late 19th century, with sculptors such as Gibbons, Rysbrack, Westmacott, Flaxman and others producing a range of monuments often comprising large and complex architectural arrangements. At the same time, fairly simple marble wall tablets with incised and gilded or painted inscriptions became commonplace throughout the British Isles.

The start of the 17th century also saw the beginning of the use of marble as a decorative feature for internal floors and walls, again influenced by the architecture of Europe. One of the earliest examples in Britain is at the Queen’s House, Greenwich, where Inigo Jones, who had returned from Italy in 1614, used marble for the flooring in 1635. Dark and brightly coloured marbles, which were deemed unsuitable for sculpture, were often used to decorate and enrich grand interiors.[1]


Statuary marble has been used externally for garden statuary and sculpture, churchyard monuments and mausolea but its relative vulnerability to frost and other atmospheric conditions meant that limestones, sandstones and granites became established as the preferred materials for external stone pieces.[2]

Even in an internal location, marble monuments are subject to a range of processes that can cause deterioration. Moisture is usually the key agent of decay, with condensation or penetrating and rising damp (often the result of a poorly maintained roof or rainwater goods) leading to direct surface erosion, soluble salt action and corrosion of iron fixings.

  Top-down view of a badly soiled church monument
  Dust and soiling on a church monument caused by atmospheric pollutants, waxes and other applied surface materials

It should be emphasised that the most immediate consideration with any monument is the structural integrity of the piece which, if compromised, may constitute a significant health and safety risk to users of the building or surrounding area.

Of major concern is the corrosion and sometimes disintegration of iron fixings, which can occasionally lead to catastrophic failure. Larger monuments may contain dozens of metal fixings, all playing a role in keeping the various parts in balance and uniting the whole as a coherent composition. Simpler memorials may rely on just a handful of fixings. Clear indications of corrosion can be seen in rust staining, cracking, spalling and movement.

Surface soiling can be attributed primarily to airborne dust and pollutants, degraded coatings, staining through condensation or water ingress, corrosion of metallic elements and fixings, and human activity (such as previous maintenance and restoration, handling and graffiti). Conservation of monuments may therefore include partial or total rebuilding, pinning and repair of breaks and losses, re-pointing of failed and open joints, and consolidation of decaying stonework or decorative finishes.

Surface cleaning may therefore appear to be low on the priority list for marble monuments. However, it can enhance a monument and allow a clearer reading of both fine detail such as inscriptions and the sculptural whole. There is also the understandable desire to maintain a piece in its best possible condition as a memorial to an event or person and as a work of art in its own right.


Before any cleaning is undertaken, careful assessment and recording should be carried out.

As part of this initial process, an assessment of the surfaces to be cleaned must be made to get a better understanding of what might be removed by cleaning and what may be left. This must also take into consideration the residues that could be left on the surface from the cleaning process/material.

A close examination of the surface should help to identify the material, assess its condition in terms of structure and surface, understand that condition and, if possible, determine what has caused it. Any surface finishes such as the remains of painted decoration or gilding should also be located and identified. Decorative finishes on marble monuments tend to be restricted to inscriptions, heraldic devices and other minor decorative elements (for example, column fluting and capitals being picked out in gilding).[3]

  A conservator uses a cotton wool swab on the shoulder of a marble bust  
  Solvent swabbing a lightly soiled marble surface  

Analysis of a painted finish through crosssection examination or identification of paint/ pigment types can be used to distinguish original decoration, which should always be retained, from later interventions that may be removed if appropriate. A close examination of a monument’s surface should also reveal any structural defects such as hairline cracking or joint movement which may need to be addressed before cleaning.

Following close examination, careful and objective tests should be specified and undertaken before continuing with a programme of cleaning. Experience of similar projects will inform the conservator in what materials and methods should be trialled, but it is always sensible to start with the most benign procedures.

The key is to develop the tests, preferably in groups that are similar in nature (such as various mineral solvents), and to give them the time to work properly. That also means, for example, allowing time for a trial area of marble to dry out fully so that the stable cleaned surface can be judged. A wet surface can often give a false idea of the final appearance.


The decision to proceed with cleaning may be left to the conservator alone, but more often than not a range of people take part in the process. This often involves managing people’s expectations. Trials to select the most appropriate cleaning method and to establish the degree of cleaning that can be achieved without risk are essential, and the conservator should present a clear and concise explanation and assessment of the trials to the client and others responsible for decision-making. It is important that the process and materials being recommended are fully understood by all concerned, rather than just the visual result.

At the most basic level, a light dusting with a fine, soft cloth (an ‘e-cloth’ for example) or a fine, soft-bristle brush can remove a dulling layer of dust and grime. A brush should be used with a vacuum cleaner with the edges of the nozzle covered with padding (such as ethafoam). If there is any danger of loose sections dislodging, a layer of gauze can be placed over the end of the nozzle to prevent any original material being sucked up.

Mechanical cleaning may include careful removal of poorly executed fills and repairs which are obscuring areas of original surface. Extreme care should be taken using hand tools such as scalpels and fine chisels, and abrasion of the marble surface should be avoided at all costs.

Wet cleaning is likely to involve a range of detergents and/or solvents. These may be used singly or in combination. For example, a standard non-commercial formula (known to conservators as ‘Kill quick’ or the ‘V&A mix’) combines water and white spirit with a small amount of non-ionic detergent. This is applied by swab or brush and can be lightly agitated with a bristle brush before removal and careful rinsing with clean water. Wet cleaning techniques act by dissolving or mobilising deposits so it is important that these are lifted from the cleaned surface using cotton wool or absorbent paper to prevent re-soiling of the marble.

Steam cleaning can be carried out using small portable dental cleaners which have been successfully employed both in conservation studios and on site. These allow very controlled targeted cleaning to be carried out at a pressure of c3-5 bar (40-75 psi).

  A conservator directs the nozzle of a portable steam cleaner close to the surface of a marble font Marble statue of man in judge's wig and gown
  Left: using a portable steam cleaner to clean a decorative marble font. Right: a marble figure during steam cleaning.

A new generation of larger steam cleaners which superheat the water have been developed for use in building conservation. These are controllable enough for use in cleaning external marble monuments where, for example, removal of biological growth or rinsing after poulticing of sulphation* is carried out. Again, the marble should be carefully examined first and only sound surfaces should be cleaned by this method. However, these machines should not be confused or substituted with standard hot-water pressure washers or other steam machines, which can cause severe damage.

More severe staining and soiling may need to be removed with laponite*, sepiolite* or paper-pulp poultices. Over-painting, often the result of sloppy decorating of an adjacent wall surface, will need to be removed using solvents or paint strippers. Strongly alkaline products should be avoided.

Chelating agents, such as EDTA* and triammonium citrate, affect ionic bonding and are useful on some types of soiling. However, they are difficult to control on marble, and many conservators consider them too unpredictable for use on historic surfaces.

Laser cleaning of marble and other stones has been regularly carried out in the conservation studio for the last 20 years and Q-switched Nd:YAG laser systems are occasionally used on-site for specific targeted cleaning (for example on the Cosmati Pavement in Westminster Abbey). These operate by emitting rapid short pulses of light energy which are readily absorbed by a dirt layer causing it to expand and lift away from the surface of the marble. Highly effective at removing dark staining from light surfaces, the use of lasers involves a good deal of organisation, an appropriate level of training and strict adherence to stringent health and safety procedures. Concern has been expressed in the past about the discolouration of some types of decorative finish and the marble substrate itself, but recent developments have been made which aim to avoid this potential drawback.

The many proprietary marble cleaning products now available have mostly been developed for the maintenance of modern architectural surfaces and are not suitable for use on marble monuments. Often highly alkaline or acidic in nature, they can be very effective at cleaning marble but do not allow the degree of control necessary for the careful cleaning of monuments. They can also leave damaging residues on the surface and introduce harmful salts.

The removal of most types of metallic staining, however, can only be achieved by the use of chemical processes. Recipes are available for self-mixing but a number of suitable proprietary products are also available. Tests should always be carried out and the manufacturer’s instructions strictly adhered to.

  A conservator applies a layer of clay over selected areas of a wall monument, parts of which have been masked with plastic sheet A conservator brushes microcrstalline wax onto a marble statue in an alcove lined with gold leaf or gold paint
  Above left: applying a sepiolite poultice to draw out and reduce copper staining caused by the bronze elements of a marble wall monument and, above right: applying microcrystalline wax to a marble figure after cleaning


Following cleaning, a further decision must often be made in relation to the application of a protective surface coating. Again, proprietary products, such as lacquers, polishes, waterproof coatings and hard waxes, should not be used for monuments or sculptures. A standard procedure is to apply a thin layer of microcrystalline wax which can provide a degree of protection to marble surfaces which are prone to condensation (such as monuments in semi-exposed locations like cloisters or porches), are vulnerable to bat excreta, or are located in areas of heavy human traffic and are liable to frequent touching. The wax can also be lightly buffed and/or tinted with pigments to enhance the appearance of dulled surfaces.

After cleaning, exterior marble monuments can be treated with a lime shelter-coat or limewashes which will adhere well to weathered surfaces and provide a degree of protection to friable marble. They can also be used to ‘even up’ an irregularly weathered surface.

After a thorough conservation clean, only simple routine maintenance should be required. Any maintenance plan should avoid the use of harsh and potentially damaging materials and should focus on providing simple guidelines for custodians where, for example, regular dusting is required.

Maintenance guidelines should also include provisions for dealing with potential sources of damage such as graffiti or accidental spillage. If a conservator is not immediately available, the problem should not be tackled by recourse to potentially damaging ‘quick fix’ solutions.

Marble monuments convey an important record of events from the early 17th century through to the modern day and form a unique facet of British sculpture and design. Marble will continue to be used as a sculptural and decorative material but never in quite the same way and it is important that this rich inheritance is conserved and looked after properly. Cleaning of these important pieces should therefore always be a carefully planned and executed conservation procedure.




EDTA ethylene-diamine tetra-acetic acid, which is used in a range of cleaning and descaling processes

laponite a synthetic silicate related to the clay mineral hectorite

sepiolite a clay mineral, magnesium silicate

sulphation chemical reaction between calcium carbonate (the main component of limestone and marble) and sulphur dioxide (a common air pollutant which, when dissolved in rainwater, forms an acidic solution) resulting in the formation of a sulphate skin on limestone and marble surfaces.


Recommended Reading

English Heritage, Practical Building Conservation: Stone, Ashgate, Farnham, 2012

G Lott and D Smith, ‘Shining Stones: Britain’s native marbles’, The Building Conservation Directory, Cathedral Communications Limited, Tisbury, 2001

P Rogers, The Beauty of Stone: The Westminster Cathedral Marbles, Westminster Cathedral, 2008



1 Westminster Cathedral (John Francis Bentley, 1895-1903) contains over 100 different varieties of marble from 25 countries.

2 It has been noted that certain types of Apuan marble are especially durable and have survived well in an external environment in Britain. As a general conservation measure, however, vulnerable marble sculpture and statuary are often protected with covers during the winter months.

3 There are cases of colour tinting of marble statues dating to the mid 19th century produced by John Gibson and others working in the neo-classical style. It is not a finish likely to be found in church or other monuments.



The Building Conservation Directory, 2014


ANGUS LAWRENCE BA Dip Cons ACR has over 20 years’ experience working on a wide range of conservation projects including major works at Westminster Abbey, the Tower of London, Westminster Cathedral and the City of London. He is a project manager for Taylor Pearce Ltd and is an assessor for the PACR (Icon) accreditation scheme.

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