Cleaning marble

Bust of Homer, Francis Harwood, 1764. Museum no. A.8-1958.

Bust of Homer, Francis Harwood, 1764. Museum no. A.8-1958

This article contains information and advice on how to look after domestic and indoor marble. It highlights common problems, tells you what to avoid and provides practical, step-by-step instructions on how to clean and preserve marble and similar materials.

First decide if your marble has historical, aesthetic or sentimental value and whether you wish to pass it on to future generations. If you think your object has significant monetary value, consider having it valued, insured and professionally conserved.

Before you start make sure that you are actually working with marble, as there are many similar materials, e.g. alabaster or painted plaster. If in doubt, do not clean because the materials discussed below are not necessarily appropriate for imitation marble. Examine your piece in good light to establish if there are any potential problems. Look for evidence of a coating and traces of original paint or gilding. If you find any, clean around them without touching them.

Types of marble

Marble is a metamorphic rock. It is formed from limestone that has gone through a process of recrystallisation through heat or pressure. This gives it a dense crystalline structure that makes a polished surface possible. Marble can vary in colour from the whites and creams of classical sculpture to pinks, greens, greys, browns and yellows. These variations are a result of mineral impurities in the original limestone.

In the decorative arts, marble is commonly associated with statuary, but is also found in a variety of objects from furniture and clocks to light fittings and lampshades. In the home, marble is used for used for fireplaces and flooring due to its strength and durability.

Common problems

Marble, like all stone, is both heavy and brittle. When these factors are combined with poor handling or internal weakness, the marble is liable to break. Whilst smaller objects may be made in a single piece, it is not uncommon for statuary to be made in multiple pieces. This may be as simple as a bust on a socle (a separate base or plinth), as complex as a large sculpture where arms and legs have been jointed on a torso, or a result of past repairs that have been dowelled into place.

While marble is often perceived as hard wearing and durable, the same properties that make it attractive can also contribute to its vulnerability. Veining, for example, gives a decorative effect but can also be a source of weakness in the stone.

Marble can also be damaged if it is exposed to acids and strong alkalis. Lemon juice, vinegar and wine can etch the surface and remove the polish. Repeated exposure may erode the surface still further.

Is it marble?

There are very many materials that can be confused with marble, so it is important to ensure what your piece is made of before attempting to clean it. There is a list of other types of stone and artificial stone, and how to clean them, at the bottom of this article.

Once you have ascertained that the object you want to clean is marble, there are two ways you can proceed: liquid cleaning or dry cleaning.

Liquid cleaning

Solvents - take care!
Apart from distilled water, the solvents mentioned below are all listed on the COSHH (Control of Substances Hazardous to Health) Register. It is very important to read the instructions and hazard labels before you use these .
  • Distilled water - available from DIY stores and chemists, used to clean and as a neutral rinse.
  • White spirit - good for removing waxes and oily dirt, available from DIY and hardware stores.
  • 2% non-ionic detergent - available from chemists.

Gloves (plastic or Nitrile, not fabric) should be worn to protect the hands, work should be carried out in a very well ventilated area, and the minimum amount of solvent should be used.

To ensure safe handling of solvents, decant small quantities for use into glass or ceramic containers - this prevents contaminating your bulk supply. Label small quantities of solvent (use the bulk container as a guide) and store all solvents appropriately (e.g. out of reach of children and away from sources of ignition etc.). 

Basic liquid cleaning
General grime, nicotine build-up and fingerprints can usually be cleaned from unpainted marble using white spirit, or a mixture of deionised (purified) water with up to 2% non-ionic detergent added.

For stubborn areas, an equal mixture of water and white spirit with up to 2% non-ionic detergent added may be useful. This will need to be shaken regularly to maintain the mixture as an emulsion. Keep this in a clearly labelled and securely capped container and only use with Nitrile or plastic gloves.

When cleaning with deionised water use slightly dampened cotton swabs and begin in a small area (e.g. 5 sq cm at a time), renewing the swabs once soiled to avoid driving dirt into the marble instead of removing it. This will also help avoid obtrusive runs and drips that can then be difficult to remove. The degree of porosity of marble is dependent on the condition of the surface. Highly polished marble is comparatively non-porous whilst marble that has weathered or been abraded is more porous.

Detergents tend to leave a residue behind on the surface which can increase the rate of resoiling and may affect the surface in other ways in the long term. If you use a detergent in a cleaning mixture, it is important to wipe over the surface thoroughly a second time using swabs slightly dampened with water.

Dry cleaning

If liquid cleaning is inadvisable, a cleaning material such as Groomstick can be used. This is a spongy, natural rubber product that is free from moisture, solvents or chemical additives (supplier: Conservation Resources Ltd). Wrap a small amount of Groomstick around the end of a bamboo stick and roll it lightly over the surface.

Stained surfaces
Iron stains, usually a rusty orange colour, can be caused by pyrites or by iron objects in contact with the marble in combination with moisture. Pyrites are small crystals of iron sulphide which look like small black spots and create an impurity within the marble. In moist conditions they can corrode and cause small orange, brown or pinkish areas of iron staining. In the past, some sculptors picked the pyrites out and filled the resultant pinhole with wax. This wax can be lost if the marble is cleaned with white spirit.

If your marble has an all-over dark yellow-brown or orange staining this might be the result of previous treatments where a combination of linseed oil and beeswax was applied as a polish, permeating the structure and, over time, forming an oxalate skin which invariably discolours the crystalline structure. Oxalate skins are complex and almost impossible to remove.

Stain removal without risking damage to the marble surface requires skill and experience. A stone conservator may be able to reduce or remove some stains by poulticing. They will also be able to minimise the risk of spreading the stain and making it worse.

To be avoided!

Abrasives and domestic cleaning materials
Avoid using bleach on marble: it does not remove stains and may change its colour or chemically react to fix the stain permanently. Bathroom cleaners often contain harsh abrasives, are acidic (to help remove limescale) and have a range of additives designed to improve their cleaning performance. Spray cleaners have similar ingredients.

All proprietary cleaners of this type can damage marble, and can 'skin' the surface, which will then be visible as dull patches. Polishing with abrasives may increase the sheen, but also removes the surface of the marble, damaging pieces of historical or monetary value.

Traditional remedies
Avoid traditional remedies.
They often rely on a strong alkali which will affect the surface of the marble itself rather than just removing dirt - the longer it is left on, the more likely it will damage the marble surface.

One 19th-century remedy suggests that discoloured marble should be treated using a mixture of equal parts of soft soap, quick lime and caustic potash. The mixture was applied with a brush, left on the marble for several days and then wiped off. The same source recommended polishing using a mixture of soda, pumice and chalk, or simply using milk.

Using milk is never appropriate because the residues that will inevitably be left behind are acidic in themselves, will encourage mould growth and attract dirt. Traditional cleaners containing vinegar or lemon juice can have a similar unwanted effect.

Polishing and waxing

If your marble has been damaged by a treatment, has a flat surface (e.g. a table top) and is not of historical or financial value, you can get it repolished. Marble is polished with a succession of ever finer abrasives, using water as a lubricant. Each stage reduces the roughness of the surface by abrading it away until the surface is smooth and glossy.

Once polished, the surface may be waxed to enhance the gloss. This is not an appropriate treatment for sculpture, decorative art or original historical surfaces - consult a conservator for best advice.

The Dyneley Casket, 1600-10. Museum no. 24-1865

The Dyneley Casket, 1600-10. Museum no. 24-1865

 

 

 

 

 

 

 

 

 

 

 


Coade stone candelabra, 1810. Museum no. A.92-1980

Coade stone candelabra, 1810. Museum no. A.92-1980

 

 

 

 

 

 

 

 

 

 

 

 

 

 


Scagliola table top, 18th century. Museum no. W.6-1933

Scagliola table top, 18th century. Museum no. W.6-1933

 

 

 

 

 

 

 

 

 

 

 

 

 

 


Pietre dure panel, about 1675. Museum no. 810-1869

Pietre dure panel, about 1675. Museum no. 810-1869

 

 


Head of a warrior, possibly 4th century. Museum no. A.102-1956

Head of a warrior, possibly 4th century. Museum no. A.102-1956

Other types of stone and artificial stone

Alabaster

Alabaster is a translucent, fine-grained stone that is often mistaken for marble. It is soft and so easy to carve and polish. It has been used for lampshades, sculptures and other decorative objects. Like marble, it is a metamorphic rock, but is mainly composed of hydrated calcium sulphate. 'Hydrated' means that it contains water within its crystal structure, which affects its durability and how it deteriorates.

Alabaster can be dissolved by water and will be damaged by heat. Heat drives out the water from within the crystal structure and it cannot be reintroduced. The effect is an irreversible loss of translucency and the alabaster takes on a dull opaque appearance. The only way to avoid this is to avoid exposure to heat. Onyx 'marbles' have sometimes been called alabaster because they have a similar appearance but they are actually polishable limestone which is more durable than alabaster.

Cleaning alabaster
First, check the surface for traces of paint or gilding. If you find any, dust around them without touching them - leave them for a specialist to treat. If there are no traces of applied decoration, you can dust with a soft brush or clean dry cloth. Alternatively, wipe the surface gently with a cotton bud slightly dampened with white spirit. Ensure you are in a well-ventilated space and wear Nitrile or plastic gloves. Avoid water or water based cleaners.

Artificial stone

Artificial stones are manufactured from aggregates, pigments and binders to imitate natural stones. Recipes dating from the 16th century were based on marble dust, lime and glue, whilst in the 18th century Eleanor Coade set up a very successful factory making artificial stone from a fired, clay-like casting material. Coade stone was more durable than many natural stones. 19th-century artificial stones include Haddon and Pulham. Artificial stone was mainly used for architectural detail and garden sculpture but may also be found in the home, for example some fireplaces with polished finishes.

Polishable limestones

Limestones vary in composition and properties. They are a sedimentary rock, often of uniform texture. Limestones are composed mainly of calcite or dolomite, with a variety of other minerals. Hard limestones can be polished and are sometimes called 'marble', for example Purbeck or Travertine, though they are not always as durable.

Cleaning artificial stone
Artificial stone, polishable limestone and onyx 'marble' are likely to be more porous than marble, so there is a higher risk of dirt being pulled into the pores of the stone if a liquid cleaner is used. Try Groomstick (supplier: Conservation Resources Ltd), but if it doesn't work use a cotton swab slightly dampened with purified water.

Polishable limestone can have bands of different sedimentation within the stone that may result in areas that are softer, more porous and more easily eroded. Watch for loose grains of stone on the surface or on your swabs. If you see any, stop cleaning and refer your piece to a specialist.

Scagliola

This is a faux marble made from selenite (the crystalline form of gypsum), glue and pigment. The mixture is applied to a support in a marbleised pattern and sometimes includes chips of marble. Once applied, the mixture is heated and polished. The technique has existed from Roman times. It was revived in the 17th century and flourished in the 18th century, particularly in Florence. Scagliola was often employed for plinths, columns and pilasters but was also used for table tops, floors and wall and door panels. It was often finished with an oil or coloured wax. Scagliola is comparatively soft and can be damaged by knocks and bumps, and also by moisture.

Cleaning scagliola
Try Groomstick first. If this is unsuccessful, test a small unobtrusive area with a swab dampened with white spirit, but if you see anything other than black dirt on the swab, stop immediately and consult a conservator. If your test is successful, you should be able to clean with white spirit. Ensure you are in a well-ventilated space and wear Nitrile or plastic gloves. Avoid water or water-based cleaners.

Pietre dure

Pietre dure (from the Italian 'hard stone') is made from finely sliced coloured stones, precisely matched, to create a pictorial scene or regular design. There are two ways of making pietre dure. In the first method, pre-cut slices of coloured stone are laid into a stone ground of marble or slate, which has had matching recesses cut into it. The background forms part of the design. The second method is to assemble the pre-shaped slices (like a jigsaw) and stick the new pictorial scene or design to a stone support, which is not part of the design.

Both methods set the pieces in a wax-resin mixture. As this mixture ages, weak or loose areas may develop and the stone pieces may crack. The wax-resin mixture will be damaged if it is exposed to a wide range of solvents, such as white spirit and alcohol. Damaged pietre dure is best treated by a specialist conservator due to its complex construction.

Cleaning pietre dure
Examine the surface for cracked or loose pieces. If there are none, try Groomstick as the first cleaning option. If this is not does not work, use a cotton swab slightly dampened with water. Do not flood the surface with any liquid.

Porphyry

Porphyry is an igneous rock, formed from volcanic magma that cooled and hardened quickly after eruption. It is harder than granite and takes a polish well. Porphyry can be red (with white spots), green (with darker green and grey spots) or grey (with green and grey spots) - the grey tends to be noticeably softer. Red porphyry is the most common type. Porphyry is an unusual stone and is therefore sometimes mistaken for marble or ceramic.

Cleaning porphyry
Porphyry can be cleaned using the materials and methods described for cleaning marble.

If liquid cleaning is inadvisable, Groomstick can be used. Wrap a small amount of Groomstick around the end of a bamboo stick and roll it lightly over the surface.

International Training Course

The Victoria and Albert Museum welcomes applications for ‘Creating Innovative Learning Programmes’, its new one week intensive course. This is a unique training opportunity for museum professionals from overseas who are interested in attracting and programming for a range of museum audiences.

Find out more

Shop online

Marbled Bouncing Ball

Marbled Bouncing Ball

Marble effect bouncing ball.   Please Note: This toy is not suitable for children under 3 years.…

Buy now

Event - Cleaning the Morris & Co. Tapestry The Forest

Wed 11 March 2015 15:30

The Forest tapestry is one of the V&A’s most popular textiles and one of William Morris’s finest achievements.

Book online