The Art Of Mixing Custom Glazes From Raw Materials
Custom glaze making begins with curiosity, but it develops through measurement, observation, and patience. A glaze is a carefully balanced suspension of minerals that melts, moves, and transforms during firing. Small changes in silica, flux, alumina, or coloring oxides can shift a surface from glossy to satin, stable to runny, or pale blue to deep green.
For a ceramic artist, the appeal lies in developing a surface that cannot be bought straight from a jar. Raw materials create opportunities for layered colors, earthy textures, ash effects, and subtle variations that support the character of each vessel or sculpture. Amelia Johannsen’s ceramic portfolio reflects this close relationship between organic forms, tactile surfaces, and the landscapes of the Pacific Northwest and Mediterranean coastline.
Working with dry ingredients also requires respect for studio safety. Fine powders should be handled with a properly fitted respirator, protective clothing, good ventilation, and careful cleaning methods that avoid sweeping dust into the air. Weighing accurately and recording every test is equally important: a beautiful result is far more useful when its recipe can be recreated.
Understanding Raw Glaze Materials
Most glaze recipes are built from three functional groups. Silica forms the glassy structure, fluxes help that silica melt at a practical kiln temperature, and alumina adds stability and viscosity. Clay minerals such as kaolin often contribute alumina while helping the liquid glaze adhere to bisque ware before firing.
Common fluxes include feldspars, whiting, dolomite, frits, and wood ash. Each has a different chemical contribution and melting behavior. Frits are manufactured glass materials with predictable compositions, while ash and natural minerals can vary considerably from one batch to another. That variation may be desirable for an expressive surface, but it makes testing essential.
Colorants are usually added in small percentages. Copper can create greens, turquoise, or red effects in particular atmospheres; cobalt produces strong blues; iron ranges from cream and amber to brown, black, or celadon green. Titanium and rutile can encourage mottling, crystals, or breaking color, especially when a glaze moves over textured clay.
Building A Testable Recipe
Begin with a clear target rather than adding ingredients at random. Decide whether the finished surface should be glossy, satin, matte, transparent, opaque, fluid, or stable on a vertical wall. The clay body and firing schedule matter just as much. A glaze that works beautifully at cone 6 oxidation may behave very differently in a cone 10 reduction kiln.
Digital glaze calculation software can help convert a base recipe into a unity or molecular formula and reveal whether the balance of flux, silica, and alumina is sensible. It does not replace testing, however. Materials may contain impurities, and firing conditions inside the kiln can vary between shelves.
Mix a small batch first, often between 100 and 500 grams. Sieve the dry ingredients thoroughly, add water gradually, and allow the mixture to hydrate before adjusting its consistency. Record the dry weight, water volume, sieve size, specific gravity, application method, firing cone, and kiln atmosphere. These details turn an experiment into usable studio knowledge.
Balancing Color Surface And Fit
A glaze must fit the clay body as well as look attractive. If the fired glaze contracts more than the clay, it may craze into a network of fine cracks. If it contracts less, it can shiver or flake from the surface. Testing on the actual clay body is therefore more reliable than judging a recipe from a photograph or a different studio’s sample.
Surface quality depends on thickness. A thin coat may appear dry and translucent, while a heavier application can become glossy, darker, or unstable. Dip, pour, brush, and spray applications all deposit different amounts of material. Create test tiles with ridges, curves, and vertical sections to see how the glaze responds to form.
| Raw material or additive | Primary role | Typical visual or practical effect | Main point to monitor |
|---|---|---|---|
| Silica | Glass former | Clarity, hardness, gloss | Excess can make a glaze stiff or under-melted |
| Kaolin | Alumina source and suspension aid | Stability and opacity | Too much may produce a dry surface |
| Feldspar | Flux and silica source | Smooth melting and gloss | Composition varies by type |
| Dolomite | Calcium and magnesium flux | Satin texture and soft opacity | Can affect melt fluidity |
| Wood ash | Variable flux and mineral source | Natural movement, ash color, rustic variation | Batch chemistry can change significantly |
| Copper carbonate | Colorant | Green, turquoise, or red in specific firings | Volatility and glaze movement |
| Rutile | Titanium-bearing modifier | Speckling, breaking color, crystallization | Results depend strongly on thickness |
Working With Ashes And Local Ingredients
Natural materials can bring a strong sense of place to a glaze palette. Cleaned wood ash, beach sand, local clay, and mineral-rich rock may contribute distinctive textures or colors. These ingredients should be dried, crushed, sieved, and documented before use. Organic matter and soluble salts can create pinholes, crawling, or unexpected surface defects.
A raw ingredient should be introduced gradually into a known base glaze. Make a line blend or triaxial blend rather than changing several materials at once. For example, increasing ash in measured steps can show when a stable satin surface becomes glossy and fluid. The method is slower than improvisation, but it makes cause and effect easier to recognize.
Glaze preparation is part of a larger making process. Clean joins and well-prepared attachments help a glaze settle evenly around a form. For precise ceramic construction, Amelia’s guide to needle-tool scoring offers a useful reminder that surface results begin with careful clay work long before the kiln is loaded.
Reading Test Tiles In The Kiln
A test tile should show more than a single flat area. Add texture, carved lines, and a vertical edge so you can observe pooling, breaking, crawling, pinholing, and running. Place test pieces on different kiln shelves because temperature distribution can influence the result. Keep kiln stilts or catch plates beneath experimental tiles when a recipe may run.
After firing, inspect the surface in natural light and handle it carefully. Look for sharp edges, loose particles, crazing, blistering, and areas where the glaze has separated. A glossy glaze is not automatically food-safe, and a surface intended for functional ware needs additional evaluation for durability, fit, and safe use.
Photograph each test beside its recipe and firing information. Notes such as “more fluid at the bottom,” “better over textured clay,” or “color strongest at medium thickness” become valuable references over time. A glaze notebook or digital archive can gradually become a personal map of reliable surfaces.
Developing A Repeatable Studio Practice
Consistency does not eliminate surprise; it gives surprise a useful framework. Weighing carefully, testing small batches, and changing one variable at a time make it possible to understand why a glaze works. That knowledge supports both controlled collections and expressive one-off pieces.
A practical routine can include:
- Label every raw material with its supplier, date, and batch information.
- Wear respiratory protection and mix powders in a clean, well-ventilated area.
- Sieve glaze slurries consistently and record the mesh size.
- Fire line blends and textured test tiles on the clay body you plan to use.
- Keep photographs, recipes, thickness notes, and kiln schedules together.
The most successful custom glaze surfaces often emerge from repeated attention rather than a single fortunate firing. A muted iron wash, a turquoise ash glaze, or a softly breaking satin finish can become part of an artist’s visual language when it is tested across different forms and refined with intention.
Explore Amelia Johannsen’s finished pottery, decorative plates, sculptures, and abstract works through the Amelia Creations portfolio, then follow the studio’s workshops and events for opportunities to experience clay, glaze, wine, and tapas in person. Subscribe to the mailing list to stay connected with new ceramic work and upcoming hands-on sessions.