What Makes Pottery Food Safe?

Pottery has been part of human history for thousands of years, with the earliest known pottery pieces dating back over 20,000 years. Simply put, pottery refers to any object made from clay that has been hardened through firing in a kiln. Pottery includes a wide range of wares like tableware, cookware, bakeware, containers, and more. With its beauty and functionality, pottery remains a popular material in both art and daily life.

In this article, we’ll explore what makes pottery safe for food use. Pottery intended for food serving and storage requires careful construction to avoid potential health hazards like lead poisoning. We’ll look at critical factors like clay composition, firing techniques, lead testing, glazes, crazing, chipping, cleaning methods, and storage. Understanding these key aspects will help ensure the pottery you use for cooking and eating is non-toxic and safe.

Clay Composition

The type of clay used to make pottery is a critical factor in determining if it is food safe. Clays come in different varieties, each with their own properties that affect their suitability for cooking and eating.

Common clays used for pottery include:

• Earthenware – Made from low-fire clays that mature at lower temperatures. They are porous and not inherently waterproof.

• Stoneware – Made from higher-fire clays and fired at high temperatures. Stoneware is non-porous, opaque, and watertight.

• Porcelain – Made from kaolin clay and fired at very high temperatures. Porcelain is highly vitrified, non-porous, and translucent.

For pottery to be food safe, it must be made from a non-porous clay body that does not leach chemicals. Earthenware is often unsuitable for food use since its porous nature allows food particles and bacteria to enter the clay body. Stoneware and porcelain are better choices as they vitrify and become non-porous during firing.

The clay should also be lead-free and not contain impurities that can leach into food during use. Using a natural clay specifically formulated for cookware is the best way to ensure food-safe pottery.

Firing Process

The firing process is one of the most important steps in making pottery food safe. Firing clay at high temperatures causes chemical changes that turn the clay into a strong, non-porous material.

During firing, pottery is placed inside a kiln and heated to over 1600°F. The temperature is steadily increased over 8-12 hours until it reaches maximum temperature. It remains at this peak temperature for 1-3 hours. This vitrifies the clay, fusing the silica particles together and creating a glassy surface that seals the pottery.

The kiln is then slowly cooled over another 12-24 hours. This gradual heating and cooling is essential to prevent cracking and breakage from thermal shock. The transformation that occurs during firing permanently hardens the clay body and seals the surface, preventing moisture absorption.

Firing pottery above 1000°F eliminates soluble salts and makes the clay chemically inert so it will not interact with food or drink. Higher temperatures also burn off any organics in the clay body, ensuring no toxins can leach into food.

Lead Testing

Lead testing is a critical part of ensuring pottery is food safe. Historically, lead compounds were commonly used in glazes and decoration of ceramics. If not properly fired and set, this lead can leach into food and liquids, causing lead poisoning when ingested. While many modern glazes no longer contain lead, testing is the only way to be certain.

In the United States, the FDA has set standards that ceramicware must have less than 3 parts per million (ppm) of lead to be considered food safe. Reputable pottery makers will have their wares tested by independent labs to verify they meet this threshold. Conscientious crafters will also test their own homemade pottery before using it for food. Special lead test kits are available that can detect the presence of lead in glazes and decorations.

It’s important to note that even tiny amounts under 3 ppm can build up over time, especially in items frequently used to serve acidic foods that erode the glaze such as juices, tomatoes, etc. For maximum safety, lead should be undetectable. When sourcing ceramicware, aim for makers that have a stringent “no detectible lead” standard.

Glazes

Glazes are an important factor in making pottery food safe. The ingredients in glazes, how they are applied, and how they interact with the clay body all impact the safety of pottery for food use.

Glazes serve several purposes – they can make pottery non-porous and easier to clean, add decorative colors and textures, and also prevent leaching of minerals from the clay body into food. However, some glaze ingredients can be toxic, especially certain metals and minerals. It’s crucial to avoid lead, cadmium, and other heavy metals in glazes. Instead, opt for safe ingredients like feldspar, silica, kaolin, and food-safe colorants.

A properly applied glaze that has been fired to the right temperature will fuse to the clay body and create a non-porous, glassy surface that seals the pottery. This prevents bacteria from getting trapped in porous clay and prevents chemicals in the clay from leaching into food and drink. Harder, vitreous glazes are best for items that will hold food or liquids.

In summary, glazes seal and protect pottery when formulated properly with non-toxic ingredients. Careful glaze application and firing helps ensure a food-safe result.

Crazing

Crazing is a network of fine hairline cracks that can appear on the glaze surface of pottery. It occurs when the clay body and glaze cool and contract at different rates after firing. The clay contracts more than the glaze, putting stress on the glaze layer. This stress causes the glaze to crack into a fine network of lines.

Crazing creates small gaps and crevices in the glaze where bacteria, mold, and other contaminants can become trapped. Food and liquids can seep into these cracks, allowing bacteria to grow inside the crazed glaze layer. Even thoroughly washing crazed pottery cannot fully sanitize it or remove trapped food residue.

Over time, crazing tends to worsen with repeated exposure to heat, liquids, and cleaning. As crazing expands, the risk of bacterial growth increases. Heavily crazed pottery is difficult to fully sanitize and therefore not recommended for food use.

Chipping

One of the main risks with using chipped pottery for food is that it can expose the porous clay underneath the glaze. When a chip occurs, it removes part of the non-porous glaze coating that seals the clay. This reveals the clay body which is porous and can absorb liquids.

These pores in the exposed clay provide places for bacteria to hide and grow. Especially problematic areas are chips along the rim and inside the vessel itself. Bacteria entering the porous clay cannot be fully washed away. Over time, the populations of bacteria can grow to unsafe levels.

Even small chips and scratches should be closely examined before using a piece of pottery for food purposes. Discard or avoid using pottery with chips and cracks along surfaces that contact food. The risks are lower for chips on the bottom or exterior surfaces that do not come in contact with food.

In summary, chipping leads to exposure of the porous clay body which can then harbor bacteria and lead to potential foodborne illness if used for serving or storing food.

Cleaning

Proper cleaning of pottery used for food is critical to prevent bacterial growth. Here are some tips for effective cleaning:

• Handwash pottery with warm, soapy water after each use. Use a soft sponge or cloth to gently clean.

• Avoid abrasive scouring pads or cleaners that can scratch surfaces, allowing bacteria to settle in.

• Rinse thoroughly with hot water after washing to remove all soap residue.

• Allow pottery to air dry completely before storing to prevent bacterial growth in trapped moisture.

• For stuck-on food, soak in warm water before scrubbing gently. Avoid aggressive scrubbing.

• Sanitize periodically by letting pottery soak for 5-10 minutes in a bleach solution (1 tablespoon bleach per gallon of warm water).

• Check for cracks, chips, and crazing regularly. Damaged surfaces are difficult to get fully clean and can harbor bacteria.

With proper hand cleaning after each use, pottery can be kept safe for food use and prevent the spread of illness.

Storage

Proper storage is crucial for keeping pottery food-safe and preventing damage or contamination. Here are some tips:

• Store pottery somewhere clean and dry. Moisture can encourage mold growth and damage glazes.

• Avoid storing pottery near open windows or doors where it may be exposed to grease, insects, or temperature fluctuations.

• Use cabinets, enclosed shelves, or containers with lids. This protects pottery from dust, grease splatter, pests, and curious hands.

• Wrap pieces individually in soft cloth or paper to prevent scratches and chips during storage.

• Avoid stacking pieces directly on top of one another, which can cause cracking or chipping.

• Do not store pottery near appliances that generate heat or moisture like stoves, dishwashers, or sinks.

• Keep lead-glazed pottery separate from food storage areas to prevent contamination.

With proper storage habits, your handmade pottery will remain beautiful and functional for years to come.

Conclusion

In conclusion, there are several factors that determine whether pottery is safe for food use. The composition of the clay body is important – low-fire earthenware clays are more porous and require a non-toxic glaze to be food safe. Stoneware and porcelain clays are less porous and do not require a glaze to make them food safe. The firing process is also key – firing to higher temperatures makes clays less porous and less likely to leach minerals into food. Proper lead testing should be done, especially for brightly colored glazes. Glazes should be stable and non-leaching. Issues like crazing and chipping can allow food to get trapped and breed bacteria. Proper cleaning, use, and storage will also prevent long-term issues with bacteria growth. While handmade pottery always carries some risks, following best practices in clay and glaze selection, firing, testing, and care can minimize risks and keep pottery food safe for everyday use.