What Is The Enemy Of Clay?

Clay is an incredibly versatile material that has been used by potters and artists for thousands of years. However, despite its durability and moldability, clay has several “enemies” that can damage, degrade, or otherwise negatively impact it. This article will examine the main threats to clay and explain why they can cause issues.

We will cover the effects of water, air, heat, acids, alkalis, organic materials, physical damage, and biological agents on clay. Understanding what can potentially harm clay is important knowledge for anyone working with this medium. Being aware of clay’s enemies allows potters and artists to take steps to protect their creations.

Water

Water can have several damaging effects on clay. Clay’s molecular structure causes it to be hydrophilic, meaning it attracts and absorbs water molecules (Low, 1961). When clay absorbs water, it can dissolve soluble salts and minerals present in the clay body. This dissolving action damages the structural integrity of the clay (Clay-water interaction).

Additionally, absorbed water causes clay particles to swell and shrink. As water is absorbed, clay expands. This swelling stresses the rigid structural bonds in the clay, leading to cracking and warping. When the water evaporates, the clay shrinks again. This shrinkage also stresses and damages the structural integrity of the clay body (Johnston, 2018).

Clay’s tendency to shrink and swell according to its water content makes it vulnerable to water damage through dissolution, swelling pressures, and shrinkage cracks.

Air

Air can be detrimental to clay in a few key ways. As clay is exposed to air, it begins to dry out which can cause cracking and damage to clay pieces before they are fired in a kiln. The moisture in the clay evaporates when exposed to air, so keeping clay covered when not in use is important.

Air also introduces contaminants to clay that can impact its workability and properties. Dust, pollen, pollution and other particles in the air can get mixed into clay. Over time, these contaminants build up and degrade the quality of the clay ¹. It’s important to keep clay properly sealed and stored when not in use.

Letting clay air dry causes uneven drying which leads to cracks and stresses on the material. Air drying also allows contaminants onto the surface of the clay that can interfere with glazes or firings. Slow drying in controlled conditions is better for finished clay pieces.

Heat

Heat can significantly impact the chemical structure and properties of clay. According to a study by Yanti et al. (https://iopscience.iop.org/article/10.1088/1755-1315/118/1/012078/pdf), heating clay above 100°C causes the hydroxyl ions to dissipate, changing the clay’s molecular structure. As temperature increases, clay minerals like kaolinite and smectite begin to lose water molecules from their crystalline structure through dehydroxylation. This process causes the clay to become more porous and shrink in volume.

Research by Aylmore (https://onlinepubs.trb.org/Onlinepubs/sr/sr103/103-003.pdf) found that heating clay to over 400°C can destroy its swelling properties and prevent rehydration. The dehydration from heat removes the water layers between silica sheets that allow clay to expand when wet. Temperatures above 600°C may collapse the crystal structure entirely as silica and alumina reconnect into new arrangements.

In summary, heat induces chemical decomposition in clays that alters their molecular structure. This affects physical properties like swelling, shrinkage, porosity and strength that depend on clay’s hydrated crystalline form.

Acids

Acids can break down the crystalline structure of clay minerals. This occurs because acids react with the cations in clays like calcium, magnesium, sodium, potassium, and aluminum that hold the crystalline structure together. The acidic hydrogen ions replace these cations, disrupting the ionic bonds and causing the clay to lose its structural integrity (Bahranowski et al., 2022).

Specifically, the acidic dissolution causes the silicate layers in clay minerals to separate, leading to swelling, loss of strength, and increased permeability. Research shows that the initial acid attack on clays is very rapid, indicating the destructive nature of acid on the clay crystalline structure (Bahranowski et al., 2022).

Acidic dissolution also increases the compressibility and volume change tendency in clay soils. The replacement of stabilizing cations like calcium and magnesium with hydrogen ions induces a more open, porous microstructure that is more prone to compression under loading (Al-Amoudi, 2018).

Overall, clay’s crystalline structure is vulnerable to degradation by acids through cation exchange reactions and silicate layer separation. This can significantly deteriorate the engineering properties of clay soils.

Alkalis

Alkalis, also known as bases, can break down the structure of clay and cause it to dissolve or disintegrate. This is because alkalis contain hydroxyl ions (OH-) that can disrupt the silicate mineral structure of clays (1). When alkalis come into contact with clays, several reactions can occur:

Alkali-silica reaction – The alkali hydroxyl ions react with silica in the clay to form an alkali-silicate gel. This gel swells as it absorbs water, leading to internal expansive forces that crack and weaken the clay (1).

Ion exchange – Alkali cations like sodium and potassium displace and substitute for other cations present between the clay mineral layers. This expands the interlayer space and causes the clay to swell and disperse (2).

Hydrolysis and dissolution – The alkali breaks Si-O bonds, releasing soluble silicate ions into solution. With enough alkali, the clay’s crystalline structure breaks down altogether (1).

One of the most damaging alkalis to clay is lye or sodium hydroxide (NaOH). Lye is a strong base that aggressively attacks silica networks and causes montmorillonite clays to dissolve (1). Even small amounts of lye can destabilize clay over time.

To minimize alkali damage, acidic modifiers may be added to neutralize excess alkalinity. Using alkali-resistant materials like kaolin or alumina cements can also help mitigate degradation of clay from alkalis.

(1) https://www.researchsquare.com/article/rs-1572646/v1.pdf

(2) https://www.sciencedirect.com/science/article/pii/0920410590900455

Organic Materials

Organic materials like vegetation, roots, and bacteria can negatively impact clay in a few key ways. As organic matter decays in clay, it can release humic and other acids that break down and discolor the clay through oxidation and reduction reactions (Walker 1966). This can lead to staining, mottling, and other discoloration. Additionally, plant roots and burrowing organisms can create voids and channels in the clay that weaken its structure (Walker 1966). As organic matter decays, it leaves behind voids where the plants used to be. Over time, these voids allow increased permeability and migration of water, which can carry staining compounds. Finally, some organic compounds can interact with clay minerals and disrupt the lattice structure through cation exchange and replacement of interlayer cations.

Overall, the presence of organic materials like vegetation and roots in clay deposits introduces chemical and physical changes like staining, mottling, increased permeability and voids, and disruption of the crystalline structure. This can negatively impact the structural integrity and aesthetics of clay.

Physical Damage

Clay is susceptible to physical damage such as cracking, chipping, and abrasion. As clay dries, it shrinks and can develop cracks if it dries too quickly. Care must be taken to dry clay slowly and evenly to prevent cracking. Chips and abrasions can occur if clay is handled roughly or improperly stored where it can rub and bump against other surfaces.

According to Princeton University’s Office of Environmental Health and Safety, “Clay scraps on the floor, bench and other surfaces can dry and pulverize, producing an inhalation hazard due to the presence of free silica.” (Source) Proper clean-up and storage of unused clay is important to prevent it from drying, cracking, and creating dust that could be inhaled.

Cracking, chipping, and abrasion damage clay physically and make it weaker. Damaged areas are more prone to breaking when worked on further. Preventing physical damage through careful handling and storage preserves the integrity of the clay and results in higher quality final ceramic pieces.

Biological Agents

Mold, algae, and fungi can all pose biological threats to clay materials and structures. Mold and fungi can grow on the surface of clay and penetrate into the material, weakening structural integrity through the growth of hyphae (filaments) (Li et al. 2021). The pigments and acids released by mold and fungal growth can also discolor and corrode the clay surface. Algae may colonize damp or frequently wetted clay surfaces, releasing organic acids that degrade the clay. Over time, the growth of algal or fungal biomass can cause physical disruption, cracking, and spalling (flaking). Careful moisture control is important to prevent biological growth on clay. It is also best practice to use clay types that are naturally resistant to mold and algal growth (Li et al. 2021).

Conclusion

In summary, there are several key enemies that can damage or degrade clay. Water can cause clay to become mushy and loose its structural integrity. Air exposure leads to drying, cracking and shrinkage. Heat can cause clay to crack during rapid drying or melting and distortion during firing. Acids and alkalis chemically alter clay’s composition. Organic materials can discolor clay or create gases during firing. Physical impacts like dropping can crack pieces. Biological agents like mold can stain clay. Proper studio ventilation, low-silica clay, careful handling and controlled firing help minimize these risks.

The main takeaways are to keep clay from getting too wet, allow controlled drying, avoid extreme temperatures, use clean tools and surfaces, handle pieces gently, and ventilate dust. Following basic studio safety guidelines will help ensure clay artworks remain intact from start to finish.