Why Mixing Your Own Is Worth the Effort

A good ready-made glaze has its place, but there comes a point where buying it by the tub starts to feel limiting. Mixing from raw materials costs a fraction of the price per litre, gives you control over colour, surface and fit, and — most valuably — teaches you how clay and glaze actually behave together. The first recipe you mix will probably be fine. The tenth will be exactly what you imagined, because by then you will understand why it works.

Start with one reliable base recipe and learn it thoroughly before you branch out. A single clear or satin base, adjusted for colour, will keep you busy for a year and teach you more than a dozen recipes copied from different sources.

Set Up a Safe Mixing Station First

Glaze materials are fine powders, and the greatest risk in any pottery studio is inhaled silica dust. Take it seriously from day one.

• Wear a well-fitting FFP3 or P3 respirator whenever you handle dry materials, and keep it in a sealed box between uses.
• Add safety glasses, nitrile gloves and an apron. Tie long hair back.
• Mix on a smooth, damp-wipeable surface. Never dry-sweep — wipe with a wet cloth or use a damp mop.
• Store powders in labelled, lidded containers, and keep a dedicated scoop for each material so colouring oxides never cross-contaminate.
• No eating, drinking or smoking in the mixing area, and wash hands and forearms when you finish.

Keep a folder of safety data sheets for every material you buy. Note the hazards, storage advice and first aid, and check the food-contact suitability of each ingredient before you use it on domestic ware. Lead and barium are best avoided altogether in a home studio.

Reading a Recipe Properly

Most recipes are written as percentages by weight that total 100. Ingredients fall into broad roles: fluxes such as feldspar, whiting, zinc oxide or a frit, which bring the melting temperature down; silica, which forms the glass; and stiffeners such as kaolin or alumina hydrate, which stop the glaze running off the pot. Knowing which group an ingredient belongs to tells you what to change when something goes wrong.

Before you weigh anything, note the intended firing range and atmosphere, because a recipe that sings at 1280°C in reduction may look dull at 1100°C in oxidation. Also record the supplier and batch number of each material — mineral batches vary, and a glaze that suddenly misbehaves is usually a materials change rather than a mixing mistake.

Weighing, Mixing and Water

Use a digital scale accurate to 0.1g for small trials. Tare the bucket, add materials one at a time, and work in 100g batches for tests and 1000g batches for production. Combine the dry powders first, shaking them together in a sealed container, then add water gradually — around 45 parts water to 100 parts dry material is a reasonable starting point.

Let the mixture slake for several hours, ideally overnight, then sieve it through an 80-mesh sieve twice, working the slurry through with a soft brush. Aim for a specific gravity of roughly 1.40 to 1.50 for dipping glazes, thinner for spraying. To check, fill a 100ml syringe with glaze, weigh it, and divide the weight by the volume. Thick glaze pours sluggishly and coats unevenly; thin glaze gives a patchy, dry surface. A few drops of Epsom salt solution can help keep heavy particles suspended.

Test Tiles That Tell You the Truth

Never trust a new glaze to a finished pot. Make a set of bisque-fired test tiles from the same clay body you throw with, stamping or scratching a number into each one while the clay is still soft. Give each tile a flat face and a vertical face so you can see both colour development and how far the glaze runs.

Apply the glaze at three thicknesses — a one-second, three-second and five-second dip — because most glaze faults are really application faults. Record everything on the tile's entry in your notebook: clay body, bisque temperature, glaze batch number, application, firing schedule, kiln position and atmosphere. Fire your tests in a normal kiln load, not a tiny test firing, so the results reflect reality. Keep a labelled tile library in a drawer; it becomes your most useful reference.

Adjusting and Testing for Real Use

When a test disappoints, change one thing and only one thing. Crazing usually means too much flux or too little silica; a glaze that runs needs more alumina, often added as 2 to 5% kaolin. Pinholing is often about thickness or bisque dust rather than the recipe itself. Write down every change, keep the failed tiles, and remember that a recipe is only yours once you have tested it three times with the same result.

For anything destined for food, test for durability as well as looks. Leave a tile in lemon juice or vinegar overnight, run another through a hot dishwasher cycle, and check for dulling or leaching. Only then is it fair to call a glaze food-safe. Keep accurate records, test tiles and safety data for every recipe, and mixing your own glazes becomes not just a way to save money, but the most satisfying part of the craft.