Porcelain & Ceramics Knowledge

Corrosion of Glazes and Ceramic Surfaces

Glaze corrosion is the chemical and physical alteration of ceramic surfaces caused by water, temperature, dishwashing chemicals and mechanical stress. It can significantly impair the shine, hygiene, resistance and usability of a piece of tableware.

General Definition of Corrosion

The term corrosion comes from the Latin corrodere and means “to decompose”, “to eat away” or “to gnaw away”. From a technical point of view, corrosion describes the reaction of a material with its environment, resulting in a measurable change to the material. This change may go so far that the function of a component, material or system is impaired.

Corrosion is not only known in metals. In geology, it describes the decomposition of rock by water and weathering. In medicine, the term may refer to the decomposition of tissue. In metals, the best-known form is rusting. Glass and ceramic glazes can also corrode when their surface is attacked by chemical or physical influences.

What Happens During Glass Corrosion and Glaze Corrosion?

On a chemical level, components are dissolved out of the surface during corrosion processes. These can include ions of various elements such as sodium or potassium. At the affected points, the optical and physical properties of the material change.

A typical result is clouding, dulling or a matt, milky surface appearance. The surface loses its original brilliance and may appear rougher, more open-pored or stained.

Susceptibility is influenced by the material itself, the hardness and density of the glaze, the lime content and temperature of the dishwashing water, steam during drying and the dishwashing chemicals used.

Material

Hardness, density, glaze composition and firing temperature determine how resistant a ceramic surface is.

Dishwashing Process

Temperature, water pressure, chemicals, rinse aid, water hardness and drying influence the stress placed on the glaze.

Use

Stacking, rubbing, abrasion, aggressive cleaning and long periods of use can intensify signs of corrosion.

Why Dishwashers Can Promote Corrosion Processes

Every dishwasher works with water, temperature, pressure, chemicals and drying. These factors are necessary for hygienic cleaning, but they can place increased stress on sensitive or lower-quality glazes.

In combination with temperature and pressure, water acts as a transport medium. Dishwashing chemicals dissolve grease, protein, starch and mineral residues, but if they are improperly dosed or too aggressive in composition, they can also attack glazes. Especially in commercial use with short wash cycles and intensive chemicals, the stress is significantly higher than in a private household.

In addition, metallic foreign substances or flash rust from knives, peelers, baskets or other metal parts can promote corrosion on stainless-steel cutlery and sensitive surfaces. Ceramic glazes with lower hardness or density may also react more sensitively to such stresses.

Typical Triggers of Glaze Corrosion

Aggressive dishwashing chemicals

Strongly alkaline or incorrectly dosed detergents can chemically attack sensitive glaze surfaces.

High temperatures

High washing and drying temperatures increase surface stress and can accelerate corrosion processes.

Low glaze hardness

Glazes with lower hardness and lower density are more susceptible to chemical and mechanical attack.

Mechanical abrasion

Stacking, rubbing and contact between pieces of tableware can additionally wear down an already weakened glaze.

Corrosion of Ceramic Surfaces and Glazes

Surfaces of glass and ceramic materials can also corrode. In tableware, this mainly affects the glaze, the protective, glass-like surface of the ceramic body. When this surface is attacked, it gradually loses shine, density and resistance.

Ceramic qualities advertised with high physical load capacity or particular break resistance are especially critical if their glazes have not been fired at the very high temperatures typical of genuine hard porcelain. If the body is strengthened with additives, this may under certain circumstances limit the maximum possible firing temperature.

For ceramic descriptions such as “Durable”, “Resistant”, “Fine China”, “New Bone China” or similar trade names, one should therefore always ask for the material type, firing temperature and glaze hardness. A prestigious-sounding name is no substitute for technical material quality.

What Role Do Hardness, Quartz and Aluminium Oxide Play?

Glazes with a higher Mohs hardness are significantly more resistant to abrasion and corrosion. Based on practical experience, glazes with a hardness of around 6 Mohs and higher are much less susceptible to glaze corrosion than softer ceramic surfaces.

A higher quartz content and/or the addition of aluminium oxide can increase the hardness and resistance of a glaze. However, these components have higher melting points and therefore require correspondingly higher firing temperatures.

This is precisely where the difference lies between many ceramic qualities and genuine hard porcelain: materials fired at lower temperatures generally do not achieve the same glaze hardness, density and corrosion resistance.

Ceramic Types Susceptible to Glaze Corrosion

In our product knowledge section on Firing & Kiln, the relationship between firing temperature, body hardness and material quality is described in detail. In our understanding, ceramic qualities fired below approximately 1,300 °C do not deserve the quality designation of genuine porcelain.

Very high hardness and density can only be achieved to a limited extent below the corresponding gloss-firing temperatures. Ceramic qualities with lower firing temperatures may therefore be more susceptible to glaze corrosion, abrasion, dulling and hygienically questionable surface changes.

Many of these designations are trade names or fantasy names. They may give buyers the impression of special quality, but without technical information on firing temperature, glaze hardness, density and material composition, they say little about actual resistance.

How to Recognise Vulnerable Glazes

Matt surface

The glaze loses its shine and appears dull, milky or visually aged.

Rough feel

A formerly smooth surface feels rougher, more open or less dense.

Dirty appearance

Corroded glazes often appear stained, grey or shabby despite cleaning.

Abrasion marks

Mechanical abrasion and glaze corrosion often occur together and reinforce each other.

Glaze Corrosion Caused by Chemicals and Detergents

The chemical composition of the detergent used has a considerable influence on the service life of ceramic glazes. In commercial use, especially in large dishwashing systems in canteens, hospitals, hotels or care facilities, very intensive chemicals are often used for reasons of time and cost.

If thermal cleaning is partly replaced by chemical cleaning, the stress on glass, porcelain and ceramics increases. Aggressive cleaners can cause glass and glazes to “go blind”, dull surfaces and permanently reduce their original brilliance.

High-quality, densely fired hard porcelain is significantly more resistant to such stresses. Without extreme chemicals, unsuitable dishwashing processes and mechanical abrasion, porcelain can retain its consistency, shine and brilliance for many years or even decades.

Example: Glaze Corrosion in Professional Use

The following example shows typical glaze corrosion, as it can occur due to aggressive dishwashing detergents and heavy commercial stress:

Example of glaze corrosion on ceramic tableware — Example of an attacked glaze surface caused by intensive chemical and mechanical stress.

What happened? Aggressive dishwashing chemicals, especially in combination with the post-drying process, chemically attack the glaze. The surface corrodes, loses its shine and, over time, may suffer complete visual and functional wear.

If such ware is advertised as particularly hard or especially resistant, it should be carefully checked whether this claim is technically plausible. What matters are not marketing claims, but firing temperature, material density, glaze hardness and actual resistance in professional use.

Why Corroded Tableware Is Hygienically Critical

Glaze corrosion is not only an optical problem. To guests, a corroded glaze quickly appears “dirty”, “old” or “shabby”, even if the tableware has been cleaned beforehand. Especially on white tableware, matt, grey or stained areas are particularly noticeable.

The hygienic assessment is even more important. If the glaze is open-pored, rough or attacked, residues, discolourations and foreign substances can settle more easily. As a result, the item may lose its suitability as a food contact article.

Urgent note: corroded tableware must be replaced immediately. In case of doubt, it should no longer be used in guest-facing areas or in areas with direct food contact.

Recommendations for Preventing Glaze Corrosion

Use hard porcelain

Explicitly request genuine hard porcelain if you want to minimise corrosion risks as much as possible.

Check dishwashing chemicals

Cleaner, rinse aid, dosage and water treatment should be matched to the material and dishwashing system.

Question material specifications

Trade names such as “Durable” or “Resistant” are no substitute for information on firing temperature, glaze hardness and material density.

Inspect tableware regularly

Matt, rough, stained or visibly attacked glazes should be consistently replaced for hygienic reasons.

Glaze Corrosion: Defect or Material Characteristic?

Whether glaze corrosion is to be regarded as a defect of the item or as a consequence of unsuitable use depends on the individual case. On the one hand, there are ceramic qualities that are inherently more susceptible because of lower glaze hardness or firing temperature. On the other hand, even suitable ware can be damaged by aggressive dishwashing chemicals, incorrect dosing or unsuitable use.

In addition, decorative areas and coloured glazes can partially conceal optical signs of corrosion. White plates show dulling and discolouration more quickly and more honestly. That is precisely why white tableware is still considered a visible sign of hygienic cleanliness in hotels and gastronomy.

A factual assessment is therefore essential: material quality, intended use, dishwashing process, chemical use and the visible condition of the glaze must be considered together.

Why Genuine Hard Porcelain Is the Safer Choice

Genuine hard porcelain is fired at very high temperatures and has a dense, hard and resistant glaze. These properties significantly reduce the risk of glaze corrosion.

Anyone who wants to operate economically in the commercial sector over the long term should not focus solely on marketing names, design or purchase price. What matters are technical material quality, firing temperature, glaze hardness, dishwasher resistance and suitability for professional operating conditions.

In case of doubt, hard porcelain should be explicitly requested in order to largely eliminate the risk of porcelain corrosion.

Conclusion

Glaze corrosion is the chemical and physical alteration of ceramic surfaces caused by water, temperature, dishwashing chemicals, steam and mechanical stress. It manifests itself through dulling, clouding, roughness, stains and a surface that appears dirty.

Ceramic qualities with lower firing temperature, lower glaze hardness or less dense surfaces are particularly at risk. Aggressive commercial dishwashing processes can further accelerate such damage.

Corroded tableware should be replaced immediately for both visual and hygienic reasons. Anyone wishing to minimise the risk should choose genuine hard porcelain, suitable dishwashing chemicals, controlled dosing and regular visual inspection.

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