Caring for your Ceramics

Plate, Spode Ceramic Works, 1818. Museum no. C.231-1934

Plate, Spode Ceramic Works, 1818. Museum no. C.231-1934

This section contains information and advice on how to look after ceramics. It highlights common problems, tells you what to avoid and provides practical, step-by-step instructions on how to clean and care for ceramic objects.

Types of ceramic

Ceramics include all objects made from clay which are shaped when wet and hardened by heating (firing). Fired clay has been used to create both functional and decorative objects since prehistoric times. In general, the higher the firing temperatures, the more durable and less porous the ceramic can be.

The ceramic body can be left unglazed after the initial 'biscuit' firing. Glaze can be applied prior to subsequent lower temperature firing. Glazes produce a decorative glassy finish on the ceramic that provides an impermeable coating to strengthen the ceramic, making it less or even non-porous and thus suitable for storing liquids.

Ceramics can be divided into three main categories defined by their firing temperatures and the constituents of the clay:

Stoneware

Stoneware is fired at a high temperature (around 1200º-1300ºC) and varies in colour from light grey to dark red, depending on the clay. It has a strong, non-porous body. Stoneware can be unglazed or glazed

Earthenware

Earthenware is fired at comparatively low temperatures (up to 1150ºC) and ranges in colour from creamy-white to red-brown. The low firing temperature means that the clay particles are only partly fused together and there are spaces (pores) between them. Earthenware is prone to staining, because liquids are able to penetrate into the body through the pores. Earthenware pieces tend to have thicker walls than stoneware and porcelain, to add strength. Earthenware objects may be unglazed or glazed.

Porcelain

Porcelain describes ceramics with a white body fired at a high temperature.

Hard-paste

Hard-paste porcelain, also known as true porcelain, is fired at temperatures up to 1450ºC. It has a vitrified (glassy) appearance and is hard, strong and non-porous. It can be used to make very delicate objects which may be thin walled and translucent. The glaze on hard-paste porcelain is fused to the body by the high firing temperature. Exposed or broken edges can be very smooth and almost glassy in texture. Hard-paste porcelain is made from china stone and/or china clay (kaolin).

Soft-paste

Soft-paste porcelains were made in Europe in imitation of East Asian porcelains. Soft-paste porcelain has a softer body than hard-paste porcelain and is slightly porous. The glaze is fired at a lower temperature than the body and sits on it as a distinct layer. Often on soft-paste porcelain the colours appear to sink into the glaze.

Bone China

Bone china is a porcellanous body developed in the eighteenth century in Staffordshire and is still produced today. It contains a high proportion of bone ash in combination with china clay and china stone.

Click on the images below to find out more about types of ceramic.


TIle, England, 14th century. Museum no. 382-1905

TIle, England, 14th century. Museum no. 382-1905. Red earthenware tile inlaid with a depiction of St Paul. The tile was broken, probably when it was removed from its original location, and poorly repaired.

Handling

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.


Cleaning

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.

Potential problems

  • 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:
 

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.


A poorly repaired English tin glazed earthenware bowl, late 17th to mid 18th century.

A poorly repaired English tin glazed earthenware bowl, late 17th to mid 18th century.

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.

Accidental breakage

 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.

Repairing ceramics

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.


Display cabinet, China, 1720-1780. Museum no. FE.56 to B-1983

Display cabinet, China, 1780 (Qing dynasty). Museum no. FE.56 to B-1983.

Storing

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.

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