A Guide To Healthier Glazes For Food-Safe Firing

A beautiful glaze can transform a hand-thrown bowl, mug or serving platter, yet appearance is only part of its performance. When a ceramic piece touches food or drink, the glaze must mature correctly, resist wear and avoid releasing harmful substances into what people consume.

For Australian potters, “food safe” is not a casual description to place on every finished piece. A glaze may be suitable for a decorative vase but unsuitable for a coffee cup, especially when it contains soluble metals, develops cracks or has been fired below its intended temperature.

The safest approach combines a reliable recipe, accurate firing, careful surface inspection and honest labelling. Commercially manufactured glazes usually provide useful technical data, while experimental mixtures require testing before they are used on functional ware.

This matters at home, in shared studios and at weekend markets in Melbourne, Sydney, Brisbane and smaller regional communities. Buyers often expect handmade ceramics to cope with tea, citrus, tomato-based food, dishwashers and ordinary Australian kitchen habits, so makers need to understand how the surface will behave in daily use.

Start With Materials You Can Trace

Avoid unknown powders, unlabelled colourants and ingredients bought from general hardware suppliers. Ceramic stains, oxides and frits are formulated for specific uses, but their safety depends on the complete glaze recipe, the firing range and whether the finished surface remains stable.

Lead is the clearest material to avoid in food-contact work, particularly in bright low-fire colours and old or reclaimed glaze ingredients. Cadmium can also present a concern in strong red, orange and yellow colours. Some traditional recipes contain barium, lithium, manganese, copper or cobalt in amounts that may require careful control. These materials are not automatically forbidden in every ceramic application, but they should never be treated as harmless simply because they produce an attractive colour.

Choose suppliers that provide safety data, batch information and firing recommendations. Keep the original labels and record the recipe, clay body, kiln schedule and glaze thickness. Traceability becomes especially valuable when a piece is sold, displayed at a local craft market or made in a community studio where several people share equipment.

Understand What Firing Can And Cannot Fix

A kiln firing changes raw minerals into a glassy coating, but heat does not magically remove every risk. If a glaze is designed for cone 6 and is fired at a low earthenware temperature, it may remain porous, soft or chemically unstable. An over-fired glaze can run, separate from the clay body or form a surface that is difficult to clean.

Follow the manufacturer’s firing schedule rather than relying only on the number shown on the kiln. Hold times, ramp rates, kiln loading and atmosphere can influence the final result. Test tiles fired beside the work can reveal colour, gloss, running and fit before a full batch is produced.

The clay body and glaze must also work together. A glaze that appears smooth in the kiln can craze into a network of fine cracks after cooling or during repeated hot-and-cold use. A carved stoneware surface, such as the one shown in this relief carving guide, may be visually successful while still needing a separate, well-tested liner glaze if the vessel is intended for food.

Inspect The Finished Surface

Food-contact areas should be smooth, fully matured and easy to wash. Reject or relegate a piece to decorative use if it has crawling, blistering, pinholes, sharp edges, exposed porous clay inside the vessel or glaze that flakes when handled. A glossy appearance alone does not prove that a surface is safe.

Crazing deserves particular attention. Fine cracks can trap oils, milk residue and bacteria, and repeated washing can make the problem worse. A crazed mug might look charming on a shelf, but it is a poor choice for coffee, soup or other moist foods. Cutlery can also mark soft glazes, while abrasive cleaners may wear through an unstable surface over time.

Do not use metallic lustres, overglaze enamels or strongly coloured decorative finishes on food-contact areas unless the product is specifically approved for that purpose and fired as directed. Keep gold, silver, iridescent effects and unknown decals on the outside of vessels or on purely decorative pieces. Any sharp foot ring, rough base or glaze drip should be corrected before sale.

Treat Testing And Labelling Seriously

Home tests, such as soaking a piece in vinegar or lemon juice, can reveal obvious changes but cannot confirm compliance. They may show staining, colour loss or a metallic taste, yet a piece can pass a simple household test and still release unwanted substances. For work sold as functional tableware, professional leach testing is the more dependable option.

Australia’s Food Standards Code, administered through Food Standards Australia New Zealand, includes requirements for materials and articles that come into contact with food. State and territory authorities handle much of the practical enforcement, and expectations may differ according to how goods are made, marketed and sold. A studio potter supplying restaurants or selling regularly through Australian markets should check current requirements and keep evidence supporting any food-contact claim.

Use precise labels. “Decorative use only” is clearer than vague wording such as “probably food safe”, while “hand wash recommended” explains how to reduce wear without implying that a piece is suitable for every food or beverage. If a surface has not been tested, do not describe it as certified or guaranteed safe.

Packaging and presentation should reinforce the message rather than disguise uncertainty. A small care card can explain whether a mug is dishwasher-safe, whether acidic foods should be avoided and why metallic decoration must stay away from food. Clear lettering gives these instructions a professional finish; makers developing their own visual style may find ideas in this guide to hand lettering styles.

Design Functional Ware With Its Use In Mind

The safest glaze decision often begins before the clay reaches the wheel. Keep experimental colours on the exterior, leave a stable liner inside bowls and mugs, and use tested transparent or white glazes where food will sit. Plates for dry foods may face different conditions from cups holding hot, acidic drinks, so the intended use should guide the testing.

Australian kitchens can be demanding. A handmade bowl may move from a refrigerator to a warm bench, carry a tomato salad at a summer gathering in Perth or Adelaide, and then be placed in a dishwasher. Thermal shock, acids, salts and detergents all put pressure on a glaze. A surface that performs well in a quiet studio test may show weakness after months of ordinary use.

For artists selling through galleries, online shops or local makers’ markets, separating functional and decorative ranges helps customers make informed choices. Amelia Johannsen’s ceramic art portfolio demonstrates how vessels, plates and sculptural work can be presented with distinct purposes, allowing surface beauty to complement practical information rather than replace it.

A healthier firing practice is built on restraint: avoid uncertain ingredients, fire to the correct schedule, inspect every surface and test when the work will contact food. Keep detailed records, communicate care instructions and reserve unverified glaze experiments for display pieces. Visit Amelia Creations to explore nature-inspired ceramics and follow the making process with a clearer understanding of what belongs on the table and what belongs on the shelf.