Caring for your Ceramics
One of the most common causes of damage to historic ceramics is rough or careless handling. Almost all such damage can be avoided by handling pieces as little as possible, thinking ahead and using common sense.
Think through the whole process and prepare for each step. For example, how many people will you need to support and lift a large or heavy object? If it's dirty, do you have somewhere suitable to clean it that won't spread the dirt?
Remove jewellery that might scratch or catch, such as rings, bracelets or watches. When you touch something, your fingers leave behind a residue. Fingermarks can contain amino acids, peptides, salts, glucose, lactic acid, ammonia, riboflavin, oils and other sebaceous secretions as well as dirt. Many of these can cause damage if left behind on an object.
Generally speaking, it is best to wear gloves of some kind. White cotton gloves are comfortable but in hot weather they should be changed frequently to ensure sweat is not transferred through the cotton. Nitrile gloves can be less comfortable but provide a complete barrier to sweat and will not snag on the object. Latex gloves are also OK (not for metal objects), although some people are allergic to them. If gloves are not available, wash your hands at regular intervals and avoid using skin creams.
Support the object evenly - you may need to think about weight (e.g. marble busts), size (e.g. cabinets) or flexibility (e.g. paper or textiles). Support three-dimensional pieces with both hands from the strongest or bulkiest parts. Avoid picking up pieces by their handle or any parts that stick out, such as finials, spouts, knobs and the limbs of figures. These areas are weaker than the body and are the parts that are most likely to have been repaired in the past.
Most ceramics can be handled without gloves, as long as hands are clean and dry. Wear Nitrile gloves when handling unglazed ceramics or pieces with unfired, gilded or lustre decoration.
Before you start any cleaning, you need to identify your type of ceramic and other materials (such as metal mounts, ivory or wooden handles) to ensure that they will not be damaged.
Examine your ceramic in good light to establish if there are any potential problems. Remember, it isn't always necessary to remove all dirt or stains. They may have historic interest or it may be impossible to remove them without damaging the piece. Before cleaning a whole piece, test clean a small area to make sure you won't damage it.
- Firing cracks, crazing or pitting in the glaze.
- Structuraldamage e.g. chips and cracks. If you tap porcelain lightly with your fingernail it should give a clear ringing tone. A dull sound often indicates a structural flaw.
- A flaking, lifting or unstable surface.
- Exposure to water can cause or worsen corrosionof anymetal parts, which in turn can damage or stain the glaze and cause cracks.
- Some glazes are fired at a comparatively low temperature, which makes them vulnerable to abrasion. Lustre glazes, for example, have a metallic iridescent sheen that can be etched by fingerprints. Gilding is often easily abraded by repeated cleaning.
- Enamels are slightly 'raised' on the surface and may flake during cleaning if the edges are damaged. In some cases, water should be completely avoided during cleaning.
- Restorations. Repairs are always more sensitive to cleaning than the original ceramic.
- Unfired decoration; painted or metal-leaf decoration is vulnerable to damage during cleaning.
Click on the images below to find out how to clean ceramics:
Cleaning glazed earthenware, glazed stoneware
Glazed earthenware, glazed stoneware, soft paste porcelain and bone china
Although glaze will provide a barrier to liquids, earthenware, soft paste porcelain and bone china are porous and glaze imperfections are common but may not be obvious, so take a cautious approach to cleaning.
1. Use a cotton wool swab (on a cocktail or bamboo stick) dampened with warm water that has had a little detergent added (about one drop of detergent per litre of water)
2. Roll the swab lightly over the surface, don't wipe or scrub. Make sure your swab is always clean - change it if you see any dirt on it. Using a dirty swab will leave dirt behind in the cracks
3. When the surface is clean, wipe over again with water (to remove any detergent residues)
4. Blot dry with a paper towel
Black basalt vase, about 1785. Museum no. 1506-1855
Unglazed earthenware, unglazed stoneware and biscuit porcelain
Using any liquid to clean unglazed earthenware risks dirt being absorbed into the body and causing stains. Although unglazed stoneware is more resistant to staining than earthenware, some fine stonewares can mark easily, for example red stoneware and Wedgwood black basalt are prone to watermarks.
To remove dust, brush lightly over the surface using a soft bristle brush (e.g. an artist's sable brush). It is a good idea to put tape over the ferrule (the metal band between the hairs and the handle) to make sure you don't accidentally scratch the surface. Avoid cotton wool because the fibres can snag on a rough unglazed surface.
Figure with basket, About 1758-70. Museum no. C.156-1931
Check figures carefully before cleaning to identify potential problems . Figures are particularly likely to have restorations that may not be immediately apparent, most commonly on hands, feet and bocage (modelled flowers, foliage and branches used as a background). The restorations on this soft paste porcelain figure, for example, include numerous leaf tips and flowers on the bocage, one finger, and chips on the hat that have been filled and retouched. The hat has also been rebonded and retouched.
Clean flat surfaces as for glazed earthenware. For intricate or delicate areas use a soft artist's paint brush (e.g. squirrel or sable, size 4-8). It is very easy to damage delicate areas, so it is better to avoid awkward parts rather than risk causing damage.
1. Wet the brush in a small container of warm water (add equivalent of one drop of detergent per litre of water)
2. Blot excess water from the brush onto clean absorbent paper to avoid drips
3. Brush a small area of the surface at a time, for example one flower or leaf on this soft paste figure at a time
4. Repeat until the surface is clean. Repeat steps 2-4 with clean water to remove detergent residues
5. Dry the brush on clean absorbent paper, and use it to pick up any water left on the surface
Pair of figurines, porcelain
Low fired wares and soft-paste porcelain are prone to staining because of the inherent porosity of the ceramic body. Unglazed areas are particularly vulnerable, but stains can also occur in glazed ceramics if the glaze is cracked or damaged. Stains can be drawn into the body of the ceramic after contact with liquids, foodstuffs, metals or even from materials used to clean or repair objects.
Do not attempt to remove stains with water, solvents or proprietary cleaning products as these can cause the stain to spread, making it worse.
Tin glazed earthenware plate (back view), Italy
Repairs on pieces are almost always more sensitive to cleaning than the original ceramic. Some restoration materials are water soluble, especially if the repair is old. Care needs to be taken to avoid weakening or damaging the repair.
Clean with soft dry brushes (e.g. squirrel or sable, sizes 4-8) to remove loose dust and dirt. If necessary, use a cotton wool swab slightly dampened with warm water and a little detergent to clean around the repair, but avoid the repair itself. Reswab the area with clean water (no detergent) and then blot dry with a paper towel (see Glazed earthenware ).
Red stoneware teapot with unfired gold decoration, 1690-8. Museum no. C.4&A-1932
This describes painted or metal-leaf decoration that has not been hardened by firing in a kiln and is therefore very vulnerable to damage from handling and cleaning. You can clean around the decoration carefully but cleaning the unfired decoration itself should be left to a conservator.
Floor tile, A.W.N. Pugin
Victorian floor tiles
Floor tiles are common in the hallways and paths of Victorian and Edwardian houses.
These are usually of two different types described as encaustic tiles or quarry tiles. Encaustic tiles are decorated with coloured clay inlays. The leather-hard clay was stamped with an impression of the design, which was then filled with a contrasting colour liquid clay 'slip'. Once dried, the excess fill was scraped away to reveal the design. Encaustic tiles may be glazed or unglazed. Quarry tiles are unglazed and often laid in a geometric pattern of contrasting colours.
Unglazed tiles have a matt surface that tends to hold the dirt. They have often accumulated a variety of floor polishes, wax, varnish, paint or lino adhesive. Over time, the rich bright colours on the tiles become obscured by such layers.
1. Remove loose dirt and dust by brushing or vacuuming.
2. Use a scalpel to carefully remove hard deposits, paint spots or very thick varnish layers. Take care not to scratch the tile with a scalpel - you will need to judge the safest angle and pressure required.
3. Add a little detergent (one drop of detergent per litre of water) to bowl of warm water. Use a stencil brush or nail brush with natural bristles to apply the water to a small area about 10 sq cm. Using a circular motion, blot the surface with a paper towel to remove the dirt. Repeat this process, then blot dry before moving on to the next area.
It may be possible to remove waxy deposits with solvents such as white spirit, methylated spirits or a 50:50 mixture of white spirit and water with a drop or two of detergent. Use the solvent on a small swab and apply to an area about 2 sq cm at a time. Work on one tile at a time and blot clean and dry before you move on. It may seem a bit fussy to work on such a small scale in a large tiled area, but it allows you to limit your exposure to solvent fumes and work in a controllable way. Although it is often easier and quicker to use more aggressive methods, these may damage the tiles, particularly if used repeatedly over the long life of the floor.
Proprietary paint stripper can be used to remove paint or varnish. Test a small area first and follow the manufacturer's guidelines for safe usage. This should also be applied following a controlled approach as described above.
As a general rule it is best to avoid applying a sealant because they don't allow tiles to 'breathe', thus trapping damp below and encouraging mould growth. A build-up of silicone sealant can be almost impossible to remove. For housekeeping, use a mat at the doorway and vacuum or sweep regularly.
Glazed earthenware tile, Mexico. Salts are visible as long white needles around the unglazed edges
Porous ceramics may occasionally contain water-soluble salts absorbed from various sources. In dry conditions, the salts are visible as loose white crystalling powder.
Salts can occur in low fired porous ceramics such as:
- architectural ceramics, as a result of contact with cement, plaster and other building materials
- archaeological ceramics, as a result of contact with soil or salty water
- ceramics used to store foodstuffs
In some cases, salts were part of the original constituents of the clay body itself. In others, materials used for repair in the past, e.g. plaster, or inappropriate cleaning materials, may react and cause salts to form in the ceramic.
Repeated cycles of changing humidity will cause the salts within the pores of the ceramic to alter their state from solution (in damp conditions) to crystals (when dry). As the crystals tend to take up more space in the pores of the ceramic than when in solution, the pressure this exerts can disrupt the ceramic causing the glaze to flake, or the body to crumble.
Surface salts, visible as a white crystalline 'powder' can usually be gently brushed away with a soft brush, though they may reappear (and cause damage) if relative humidity fluctuates. Relative humidity measures the amount of moisture that is in the air relative to the maximum amount of moisture that the air could hold at that temperature.
Conservators use poulticing or immersion techniques for removing salts from badly affected pieces. An object with extensive salts or a flaking / crumbling surface should be referred to a ceramics conservator.
Damage through cleaning
Do not use a dishwasher to clean valued ceramics. High temperatures, high pressure water and aggressive detergents can permanently damage glazes and coloured enamel decoration.
Avoid using household bleaches or proprietary cleaning products because they can cause irreversible damage. Cleaning liquid can penetrate the ceramic, taking dirt with it. This can cause new stains or make old stains worse. Often the effect is not noticeable until the object has dried. Abrasive creams and cleaners will damage delicate decoration such as gilding, lustre or enamels and in the worst case, dull the glaze itself.
Breakages and repairs
Faults can occur during manufacture as a result of the constituents of the clay or glaze, poor fabrication techniques (e.g. how well a handle was attached) or inconsistencies in the firing process. Areas of inherent vulnerability include firing cracks, crazing or pits in the glaze. Many inherent problems in ceramics are directly related to the type of ceramic body and decoration, for example the porosity of earthenware means that it is prone to staining if it gets wet.
Restorations and repairs
Old repairs often indicate structural weakness and can disguise problems underneath. Some modern resins allow breaks to be joined almost invisibly. If the join hasn't been retouched, you should be able to spot it using a magnifying glass. Areas of loss are often filled with plaster or resin materials and then painted to disguise them. In time the paint will discolour or flake away.
In some cases, the whole object may have been coated with paint or lacquer as the last step in its restoration - at first glance this may look like the glaze but feels somewhat 'plastic'. Some porcelain restorations can be spotted by holding the object up to the light, where many repaired breaks or filled areas will appear darker than the original. A handheld ultraviolet light can help reveal restored areas.
If you are likely to make an insurance claim, photograph the scene of the accident before anything is moved. Collect all the fragments, no matter how small. Fragments can travel quite a distance after impact, so look carefully to find all the pieces.
Place larger pieces into a tray or box, padding or loosely wrapping them with clean tissue or acid-free paper. Use self-sealing bags for small pieces. Avoid sticky labels, which can be difficult to remove. Try not to touch the broken edges as fingermarks can make rebonding difficult. Resist the urge to try to fit any pieces back together - edges are always fragile. Consult a ceramics conservator for the best possible repair.
In theory bonding a broken ceramic back together should be straightforward, but the sheer number of poor quality repairs found - misaligned edges, adhesive that has stained porous ceramic bodies, or lumps of excess adhesive along the break line - highlight the problems that can be encountered. Sometimes the damage caused by amateur repairs can be irreversible. If you value your ceramic, leave bonding of broken pieces to a conservator.
One of the reasons for difficulties with home repairs is that common household adhesives are inappropriate. Some are too thick or discolour, whilst others bond almost instantaneously, giving one brief chance to get it right. All such products are hard to remove and will make any future repair work more difficult and time consuming. Ceramics conservators often use specialist adhesives that are not readily available to the public.
Ceramics can usually tolerate a wide range of environmental conditions without being damaged. There are some notable exceptions, e.g. ceramics in which salts are dormant but where problems will be initiated by fluctuating relative humidity.
In rare cases, there may be a manufacturing fault that can cause cracks to develop in the body or crazing in the glaze, particularly where there are sudden changes in temperatures, for example from direct sunlight or spotlights.
Lastly, old restorations or repairs may be more vulnerable to the environment. For example, some restoration materials used to fill or retouch a loss may discolour if exposed to strong light or if stored in the dark.
However, the main cause of damage to ceramics is impact damage. Try to avoid displaying ceramics in areas where there is passing traffic or where you may need access behind them, for example window sills in front of an opening window.
Display cabinets are a good option. If several pieces are displayed together, make sure they are not too crowded and aren't touching each other. Avoid hanging pieces by their handles, as these are often a weak point, particularly if they have been damaged or repaired in the past.
Vibration can be a problem when displaying ceramics. A busy road outside or foot falls on a springy floor inside a home can cause ceramics to 'creep' and they may bump into other pieces or fall from the shelf. One way to prevent creep is to place a piece of chamois leather under the ceramic. This is also a good way of stopping ceramics with an uneven base from wobbling. Avoid rough surfaces as they can scratch the base.
Commercially available display or mounting waxes are another way to prevent creep, but take care to ensure that it does not stain your object. Take a small amount and make it into 3-4 balls, place at regular intervals underneath the ceramic and press down gently. To remove the ceramic, hold it firmly by its base and turn gently. Residues can be removed with a cotton swab barely dampened with white spirit. Too much liquid can draw residues into a porous body such as earthenware.
Mounts for ceramics
Mounts are often used to show decorative ceramics that are in good condition but they aren't always suitable for cracked or restored pieces. Mounts need to be the right size for the piece - if they are too tight they can chip the edges, whilst if they are too large they won't hold the piece securely.
Museums often use inert plastic (e.g. Perspex) for mounts, as seen here, but there are many other safe options. Proprietary adjustable plastic hangers, called wall plate stands (supplier: Dauphin), wooden display stands and grooved shelves in display cupboards are all suitable. Plastic coated metal sprung plate hangers should only be used if the dish is in good condition. Bare metal hangers can cause scratches or chips and will stain the ceramic if it corrodes. Avoid mounts with hard sharp edges or using metal pins to stop plates sliding forward, as they can chip or scratch unless they are padded.
Produced by the V&A Ceramics and Glass Conservation Studio.