Free Pottery learning guide
Mastering Intermediate Glaze Application and Firing Techniques
Mastering Intermediate Glaze Application and Firing Techniques — a free intermediate-level guide covering intermediate glaze application and firing...
What you will learn
- Understanding Glaze Composition and Chemistry
- Glaze Application Techniques for Depth and Texture
- Precision Glaze Mixing and Preparation
- Understanding Firing Dynamics and Kiln Atmospheres
- Advanced Glaze Layering and Special Effects
- Firing Methods for Controlled Glaze Reactions
- Glaze Defects and Troubleshooting
- Glaze Testing and Documentation
- Integrating Glazes with Form and Function
- Experimental Glaze Techniques and Alternative Materials
1. Understanding Glaze Composition and Chemistry
The Alchemy of Fire: How Raw Minerals Become Glaze Picture this: You’ve just pulled a kiln full of plates after a high-fire cycle. Most of the glazes emerged glossy and predictable, but one pot near the top shows a matte surface marred by tiny craters that look like someone poked the glaze with a needle—pinholing. The glaze recipe is the same you’ve used for years. The firing schedule hasn’t changed. Yet, today, something went wrong. Again. Glaze chemistry isn’t magic, but it can feel like alchemy when a familiar recipe suddenly fails. The difference often comes down to understanding what’s really in your glaze and why those ingredients behave the way they do under heat. This chapter bridges the gap between raw materials and the fired surface, showing how silica, fluxes, colorants, and opacifiers interact at a molecular level and how that knowledge turns “mystery defects” into predictable results. By the end, you’ll be able to look at a glaze recipe and anticipate not just how it will melt, but when and where it might crack, crawl, or devitrify. You’ll know why a blue glaze from one supplier behaves differently than one from another, even if the colorant percentages look identical. And most importantly, you’ll gain the confidence to troubleshoot common issues like crawling or pinholes by adjusting chemistry rather than just tweaking your technique. --- The Core Ingredients: Building Blocks of Every Glaze Every glaze begins with a handful of essential players. While recipes vary wildly—from traditional ash glazes to modern frits—most fall into four fundamental categories: - Silica (SiO₂): The skeleton - Fluxes: The melters - Colorants: The artists - Opacifiers and Modifiers: The engineers Together, these components form a recipe that melts, flows, and solidifies into a glassy surface. But their roles aren’t static. A single material can act as both a flux and a colorant. A flux can become an opacifier when combined with others. The chemistry is fluid—literally. Silica: The Structural Backbone Silica, usually sourced as flint, quartz, or sand, is the primary glass-forming oxide in glazes. It provides structural integrity and durability. Without enough silica, a glaze won’t vitrify—it will remain weak, porous, and prone to leaching. - Role: Forms the SiO₂ network that becomes glass upon cooling. - Melting Point: Pure silica melts at 1713°C (3115°F), far too high for most kilns. - Purpose in Glazes: Must be balanced with fluxes to lower the melting point while maintaining strength. Critical Point: Too little silica = weak, unstable glaze. Too much = refractory, unmelted glaze. Silica grains don’t melt directly. Instead, they dissolve into a molten flux bath. The more flux present, the faster silica dissolves and the lower the overall melting temperature. This …
2. Glaze Application Techniques for Depth and Texture
Mastering the Brush: Techniques for Dynamic Glaze Surfaces A single brushstroke can transform a flat glaze into a living landscape. Consider the work of ceramic artist Lisa Orr, whose layered matte and gloss glazes create the illusion of erosion on a vase—each stroke deliberately thin, allowing the underlayers to subtly bleed through. The difference between a novice’s muddy glaze and Orr’s depth often comes down to technique rather than chemistry. This chapter moves past the basics to explore how application methods shape the final glaze, whether through deliberate movement, controlled layering, or strategic thinning. --- Application Fundamentals: Beyond the Basics While basic application focuses on even coverage, intermediate techniques emphasize control over distribution. The key lies in understanding how different tools interact with glaze viscosity and the ware’s surface. Understanding Glaze Rheology in Application Glaze viscosity determines whether a brush leaves streaks, a sponge creates texture, or a spray delivers a fine mist. A glaze that’s too thick resists flow, trapping brush marks or sponge pores, while one that’s too thin can puddle or run. Most studio glazes fall between 1.4 and 1.6 specific gravity, but this can vary widely based on silica content and flux ratio. Tip: Test a small batch on a sample tile before committing to a large piece—adjust water content incrementally to find the sweet spot where the glaze moves smoothly but doesn’t slump. Surface Preparation: The Hidden Step Even the best application technique fails on unprepared ware. Dust, fingerprints, or residual oil from the forming process can repel glaze, leading to bare spots or crawling. Pro move: Wipe bisqueware with a damp sponge just before glazing, then let it dry completely. For textured surfaces, a quick blast of compressed air can dislodge debris from crevices. --- Brush Techniques for Controlled Depth Brush application isn’t about covering the surface—it’s about orchestrating where glaze lands and how it behaves. The Dry Brush Effect Dry brushing creates a weathered, aged look by depositing glaze only on raised surfaces. To achieve this: - Use a stiff, wide brush (e.g., a hake or decorating brush). - Load the brush lightly with glaze, then wipe most of it off on the rim of the glaze bucket. - Drag the brush across the ware in one direction, allowing the bristles to catch only on texture or raised areas. Best for: High-contrast pieces where you want to emphasize form over color, such as sculptural work or functional ware with carved details. Layered Brushwork Building depth through layers requires patience and a clear plan: 1. Base Layer: Apply a mid-tone glaze (e.g., a celadon or iron oxide wash) with a soft brush, working in broad strokes. Let it dry completely. 2. Second Layer: Use …
3. Precision Glaze Mixing and Preparation
The Hidden Cost of a Poorly Mixed Glaze A single batch of glaze, improperly mixed, can ruin an entire kiln load. Even a slight variation in particle distribution can leave your ware streaked, pitted, or with uneven color. Worse, inconsistencies in suspension can lead to crawling, pinholes, or even glaze crawling off the piece entirely during firing. These aren’t just aesthetic flaws—they’re material waste, wasted time, and lost confidence in your process. The difference between a glaze that’s ready for the kiln and one that’s a liability often comes down to precision in mixing and preparation. This chapter moves past basic mixing techniques and focuses on the factors that separate a glaze that works from one that doesn’t. It’s not just about following a recipe—it’s about controlling variables, testing assumptions, and knowing when—and how—to adjust. --- Understanding the Core Variables in Glaze Mixing Precision mixing begins with recognizing what can—and will—change during the process. These aren’t just theoretical concerns; they’re real-world factors that affect every batch you make. Weight vs. Volume Measurement: Why Accuracy Matters - Volume measurement (e.g., cups, scoops) introduces variability based on: - Particle packing: Different materials settle at different rates. A cup of silica has more void space than a cup of kaolin due to particle shape and size. - Moisture content: Materials absorb humidity differently. A "cup" of feldspar may weigh 10% more in humid weather. - Tool calibration: Measuring cups and scales drift over time. A digital scale that’s off by 10g can throw off a glaze batch significantly. - Weight measurement (grams) eliminates many of these variables but introduces others: - Requires a calibrated scale—a cheap or uncalibrated scale can misread weights by several grams. - Assumes homogeneous materials—if your kaolin has large chunks of unmilled material, weight alone won’t compensate. - Doesn’t account for volatiles like water in raw materials (e.g., hydrated borax). Tip: Always weigh materials when possible, especially for critical batches. Use volume only when weight isn’t feasible (e.g., for very large batches where scale capacity is limited). Keep a log of material weights over time to spot drift in your tools or materials. Suspension and Particle Behavior Glazes are suspensions, not solutions. This means the solid particles (silica, feldspar, colorants) must remain evenly distributed in the liquid medium (usually water) during mixing, application, and drying. Several factors disrupt this: - Particle settling: Heavier particles (e.g., iron oxide, zircon) sink faster than lighter ones (e.g., silica). - Flocculation: Some materials cause the glaze to clump, leading to uneven distribution. - Deflocculation: Over-dilution or incorrect deflocculant use can cause the glaze to separate or run off the ware. Real-world implication: A glaze that looks perfect in the bucket may separate by …
4. Understanding Firing Dynamics and Kiln Atmospheres
The Heat Behind the Magic: How Firing Transforms Glaze Picture this: A pot sits in a kiln, its surface a blank canvas of matte white glaze. You hit the switch, and for the next twelve hours, the kiln’s temperature climbs like a slow, deliberate tide—from room temperature to molten glow—before retreating again. When you open the door, something extraordinary has happened. The glaze isn’t white anymore. It’s deep cobalt blue with subtle green mottling, its surface alive with movement and depth. The transformation seems almost alchemical. But the real magic isn’t in the kiln itself—it’s in understanding how heat, time, and atmosphere work together to coax these reactions into existence. This chapter isn’t about what glazes are made of—that was covered in earlier modules. It’s about how we fire them. The firing process doesn’t just melt the glaze; it breathes life into it. Oxidation, reduction, neutral atmospheres—each alters molecular behavior in subtle and dramatic ways. Ramp rates and cooling curves don’t just get you to temperature; they control crystal growth and color development. And kiln placement? It’s the silent choreographer of heat distribution, deciding which side of your pot catches the light and which stays in shadow. By the end of this chapter, you’ll move beyond simply pressing “start” on a kiln. You’ll see firing as a deliberate dialogue between artist and material—one where control isn’t optional, but essential. --- Kiln Atmospheres: More Than Just Air Kiln atmosphere isn’t just background—it’s an active participant in the glaze’s transformation. The three primary types—oxidation, reduction, and neutral—dictate how oxygen interacts with glaze components during firing. These atmospheres don’t just sit there; they react, and those reactions can turn a predictable glaze into a revelation or a disaster. Oxidation: The Controlled Burn Oxidation is the most straightforward atmosphere. It’s what happens when there’s an abundance of oxygen throughout the firing. In electric kilns, this is the default state because the heating elements (typically silicon carbide or molybdenum disilicide) don’t consume oxygen in the same way gas burners do. What happens in oxidation? - Organic matter burns away cleanly. - Colorants stabilize predictably. Copper, for example, reliably produces turquoise or blue in oxidation, while cobalt gives consistent deep blue. - Glazes mature evenly, with predictable gloss and color development. But oxidation isn’t without nuance: - High-alkali glazes can become overly fluid, risking running or crawling, especially near the top of the kiln. - Some metallic colorants (like tin-based opacifiers) appear more opaque and stable. - Volatile colorants, such as cadmium, are safer in oxidation because they don’t vaporize unpredictably. Tip: In oxidation, glaze color often reflects the raw oxide color more directly. Cobalt oxide (CoO) is black when raw, but in an oxidized glaze, …
5. Advanced Glaze Layering and Special Effects
The Alchemy of Intentional Chaos: Crafting Glaze Interactions The kiln’s muffled roar swells to a crescendo. A piece of work you’ve layered with copper red over an iron-spot glaze now sits stacked with three others, each one an experiment in controlled unpredictability. The firing schedule climbs past the critical point where alkaline fluxes begin to liquefy the silica network. You know the glazes will move, but you don’t know how—only that the interaction will be fast, irreversible, and entirely yours. This is where glazing stops being decoration and becomes collaboration: a conversation between intention and kiln magic. Layering glazes isn’t stacking; it’t strategizing. You’re not just adding color—you’re engineering chemical migration, viscosity gradients, and phase separation. The goal isn’t perfection, but controlled complexity. The best layered pieces emerge not from fear of error, but from understanding how to invite it—then guide it. --- Designing Multi-Layered Glaze Systems: Color, Contrast, and Chemistry Designing layered glazes begins long before the brush touches the pot. It starts in the glaze recipe book and ends in the kiln’s thermal history. The interaction between layers depends on three key variables: glaze chemistry, application timing, and firing dynamics—all of which were introduced in earlier chapters. Here, we focus on orchestration. Color Layering: Building Depth Through Contrast Contrast isn’t just visual—it’s chemical. When you layer a cobalt-based blue over a manganese-rich purple, the cobalt acts as a strong flux, lowering the melting point of the base glaze. As the kiln heats, the blue layer begins to melt first, flowing into the purple and creating interaction halos around sharp edges. Use these strategies for intentional color layering: - Contrast in Opacity: Pair a translucent flux-heavy glaze (e.g., a boron-rich clear) over an opaque tin-based white. The white will act as a reflective base, making colors appear more saturated and depth-enhanced. - Temperature Staggering: Apply a high-temperature glaze (cone 8–10) over a mid-range glaze (cone 5–7). The lower layer will remain more viscous longer, resisting flow and preserving sharp undercut edges. - Color Migration Control: Use iron oxide in the base layer and copper oxide in the top layer. During firing, copper will diffuse into the iron-rich layer, creating a gradient from turquoise to olive green—provided the firing ramp is slow enough (under 120°C/hour) through the 800–1000°C range. Pro Tip: When layering colors, always apply the more fluid glaze on top. A fluid glaze will flow into a viscous one, creating organic blends. The reverse often results in cracking or crawling. Texture Layering: From Matte to Shine Texture isn’t just about surface feel—it’s about light interaction. A satin matte base under a glossy transparent top will create a soft diffusion effect, while a matte top over a glossy base …
6. Firing Methods for Controlled Glaze Reactions
Specialized Firing: Mastering Controlled Glaze Reactions The first time ceramic artist Elena saw a saggar-fired piece emerge from the kiln, she thought the glaze had failed—until she realized the apparent defects were the goal. A crackled surface shot through with metallic copper flashing, where the glaze had intentionally been pushed to its limits. Unlike traditional firings where consistency is the target, this was a controlled collapse: the glaze reacting not just to heat, but to containment, combustion, and chemistry in a confined space. Elena’s mistake wasn’t in the process—it was in her expectations. She had assumed glaze behavior should always be predictable. But in specialized firings, unpredictability isn’t a flaw; it’s the medium. This chapter assumes you already understand the roles of silica, fluxes, and colorants in glaze behavior. You know how layering and application techniques influence outcomes. What changes here is the firing environment itself—shifting from neutral control to active manipulation through containment, atmosphere, and timing. The goal isn’t to eliminate variables, but to choreograph them. You will learn to use saggars, lusters, and raku not as alternative firing methods, but as tools for eliciting specific glaze reactions that go beyond what standard kilns can achieve. --- Saggar Firing: Confinement as Creation Saggar firing is not about protecting ware from the kiln, but about creating a miniature combustion chamber where fuel, vapor, and glaze interact under controlled isolation. It is the opposite of clean firing—it thrives on partial combustion, organic smoke, and chemical residue trapped within a ceramic or metal container. How Saggars Work: Chemistry in a Box A saggar is a refractory container that holds your piece and a combustion medium together. The medium—sawdust, salt, seaweed, copper carbonate, or even banana peels—burns during firing, releasing gases and volatile compounds. These interact with the glaze surface in a localized reduction zone, even when the kiln atmosphere is neutral or oxidizing. - Combustion mediums determine the character of the reaction: - Organic materials (sawdust, straw, coffee grounds): Release carbon particles and reducing gases (CO, H₂) that can create carbon trapping, metallic flashing, or mottled carbon marks. - Salt or soda ash: Introduce sodium vapor that can flux the glaze surface slightly, creating a glossy, crystalline texture. - Metal salts (copper carbonate, cobalt chloride): Vaporize and migrate into the glaze, creating vivid iridescence or speckling. - Sulfur sources (gypsum, eggshells): Can produce subtle yellow or orange halos through sulfide formation. The glaze must be formulated for saggar work—it should mature at a lower temperature than standard glazes to allow surface interaction without full vitrification. Overly dense glazes resist vapor penetration; underfired glazes absorb too much residue, leading to blistering or pitting. Tip: Use glazes with a slight matte or satin finish. …
7. Glaze Defects and Troubleshooting
The Anatomy of a Failure Imagine this: You have spent weeks sculpting a complex form, applied a meticulously layered combination of glazes as detailed in Advanced Glaze Layering and Special Effects, and executed a firing sequence based on the principles of Firing Methods for Controlled Glaze Reactions. You open the kiln expecting a masterpiece, only to find the glaze has pulled away from the surface in islands of glass, or the surface is peppered with tiny, stubborn holes. To the novice, this is a disaster. To the intermediate potter, this is a diagnostic map. A glaze defect is rarely a random occurrence; it is a chemical or physical signal that something happened during the transition from raw powder to molten glass to solid surface. By analyzing the visual evidence, you can pinpoint exactly where the system failed—whether in the chemistry, the application, or the kiln atmosphere. Surface Tension and Adhesion Failures When a glaze fails to bond with the clay body or pulls away from itself during the melt, the result is usually a failure of surface tension. Crawling Crawling occurs when the glaze pulls away from the clay surface during the melt, leaving bare patches of ceramic. It looks like the glaze has "beaded up" like water on a waxed car. The Root Causes: Surface Contamination: The most common culprit. Dust, oil from fingertips, or leftover wax resist prevent the glaze from adhering to the bisqueware. Excessive Shrinkage: If the raw glaze shrinks significantly more than the clay body during drying, it develops micro-cracks. During the melt, the surface tension pulls these cracks open into large gaps. Over-application: A glaze layer that is too thick creates high internal tension. As the glaze melts, the weight and pull of the molten glass cause it to slump and pull away from the edges. High Clay Content: Over-reliance on clay as a suspending agent in the glaze recipe (mixing errors detailed in Precision Glaze Mixing and Preparation) increases drying shrinkage. Corrective Strategies: Pre-glaze Cleaning: Wipe bisqueware with a clean, damp sponge to remove dust. Adjust Application: Thin the glaze with a small percentage of water or adjust the dipping time to ensure a consistent, moderate thickness. Recipe Modification: Reduce the percentage of kaolin or ball clay in the recipe and replace it with a non-plastic equivalent if shrinkage is the primary cause. Pinholing and Blistering While they look similar, pinholes and blisters are caused by different stages of gas escape. Pinholing appears as tiny, needle-like holes in the glaze surface. These are the "exit wounds" of gases escaping from the clay or glaze. Blistering manifests as larger, bubble-like craters, often with a rim of glaze around the hole. This occurs when the …
8. Glaze Testing and Documentation
The Myth of the "One-Off" Success Imagine you’ve spent three weeks throwing a series of complex vessels. You apply a new experimental glaze, fire the kiln, and open it to find one piece that is absolutely perfect—the exact depth of color and satin texture you envisioned. You reach for the other five pieces in the series, only to find they are either runny, matte, or a completely different hue. For the intermediate potter, this is the "glaze lottery." The frustration isn't that you can't achieve a great result; it's that you can't repeat it. This inconsistency usually stems from a lack of controlled testing. In professional ceramics, the goal is to move from "happy accidents" to "predictable outcomes." To do this, you must stop treating your finished ware as the primary testing ground and start treating the test tile as your most important tool. Designing Controlled Glaze Tests A controlled test is one where only one variable is changed at a time. If you change the glaze recipe, the application thickness, and the kiln position all in one firing, you will have no way of knowing which factor caused the final result. The Single-Variable Principle When refining a glaze, isolate your variables. If a glaze is slightly too matte, do not simultaneously increase the firing temperature and add more Silica (SiO₂). Instead: 1. Variable A (Chemistry): Increase Silica by 2% while keeping the temperature constant. 2. Variable B (Temperature): Keep the recipe identical but fire to a higher cone. 3. Variable C (Application): Apply a thicker coat of the original recipe. By isolating these, you identify exactly where the "failure" is occurring—whether it is a chemical imbalance (refer to Understanding Glaze Composition and Chemistry) or a firing issue (refer to Firing Methods for Controlled Glaze Reactions). Determining What to Test Before mixing a batch, define your objective. Are you testing for: Stability: Does the glaze run or blister at a specific temperature? Color Response: How does a specific colorant, like Copper (CuO), react to different base glazes? Interaction: How does the glaze behave when layered over another (refer to Advanced Glaze Layering and Special Effects)? Fit: Does the glaze craze or shiver on a specific clay body? The Architecture of the Test Tile A flat slab of clay is rarely sufficient for a comprehensive test. To truly understand a glaze's behavior, your test tiles must mimic the geometry and conditions of your actual work. Verticality and Flow Glazes behave differently on a flat surface than they do on a vertical wall. To test for runniness or viscosity, your tiles should include: Vertical Walls: A "L-shaped" tile allows you to see if the glaze streaks or pools at the bottom. Curved …
9. Integrating Glazes with Form and Function
The Conflict of the "Perfect" Glaze Imagine a meticulously thrown porcelain vessel with a thin, elegant rim and a narrow neck. You apply a high-viscosity, heavy-zinc glaze that creates a stunning, crystalline variegated surface. Upon opening the kiln, the piece is visually breathtaking, but the narrow neck has completely fused to the kiln shelf, and the glaze has pooled so thickly at the base that it has caused the foot to slump, compromising the structural stability of the piece. This is the classic tension of the intermediate potter: the conflict between aesthetic ambition and functional reality. A glaze is not merely a "paint" applied to a finished form; it is a glass coating that interacts chemically and physically with the clay body during the firing process. When we integrate glaze with form, we are managing a relationship between fluid dynamics, thermal expansion, and human ergonomics. Functional Requirements and Glaze Selection Selecting a glaze based solely on a test tile is a common mistake. A tile provides a 2D representation of color and texture, but it does not account for how a glaze behaves on a vertical wall, a horizontal interior, or a high-wear surface like a dinner plate. Food Safety and Chemical Stability For functional ware, the primary consideration is leaching. As covered in Understanding Glaze Composition and Chemistry, the balance of fluxes and silica determines the stability of the glass matrix. Acid Resistance: Glazes used for food—especially those holding acidic substances like citrus or tomato sauce—must be chemically stable. If a glaze is under-fired or has an improper ratio of alumina to silica, acids can leach out metal colorants or fluxes. Crazing and Bacteria: While often viewed as an aesthetic defect (as discussed in Glaze Defects and Troubleshooting), crazing (a network of fine cracks) in functional ware creates microscopic pockets where food particles and bacteria can lodge, making the piece difficult to sanitize. Surface Texture: A highly textured or "cratered" glaze may look organic and modern, but in a bowl or mug, it can be abrasive to the tongue or impossible to clean thoroughly. Durability and Wear The "hardness" of a glaze is largely a function of its silica and alumina content. Utilitarian Surfaces: For plates and mixing bowls, prioritize glazes with high alumina levels to increase scratch resistance. The Cutlery Test: A functional glaze should be able to withstand the repetitive scraping of metal utensils without developing "metal marking" (grey streaks left by stainless steel). Thermal Shock: For oven-to-tableware, the Coefficient of Thermal Expansion (COE) of the glaze must closely match the clay body. A mismatch leads to shivering (where the glaze peels off the form), which creates a significant safety hazard in food service. Glaze Application and …
10. Experimental Glaze Techniques and Alternative Materials
The Alchemy of the Unknown: Beyond the Commercial Jar Imagine walking through a forest after a heavy rain and noticing a streak of vivid, mineral-rich orange clay clinging to a rock, or visiting a local bakery and seeing a bucket of hardwood ash destined for the compost. To the untrained eye, these are waste products or geological curiosities. To the experimental ceramicist, they are raw sources of fluxes, colorants, and modifiers. While commercial glazes provide consistency and safety, they operate within a narrow range of "predictable" chemistry. Experimental glazing is the process of intentionally introducing instability—using raw, unrefined materials to trigger reactions that pre-mixed products cannot replicate. This is where the transition from "applying a glaze" to "engineering a surface" occurs. Harvesting Local Materials Incorporating natural materials allows a potter to anchor their work to a specific geography. However, because these materials are unrefined, they introduce variables that require the rigorous Glaze Testing and Documentation protocols established in previous chapters. Wood Ash as a Flux Wood ash is one of the oldest experimental materials in ceramics. Because trees absorb minerals from the soil, the resulting ash is rich in calcium, potassium, and magnesium—all of which act as alkaline earth fluxes. Processing: Raw ash cannot be added directly to a glaze. It must be "washed." This involves mixing ash with water, letting it settle, and siphoning off the liquid. This process removes excess soluble potassium (which can cause unpredictable bubbling) and leaves behind the stable mineral oxides. The Effect: Ash glazes are prized for their "runniness" and the formation of organic streaks and "tears" as the glaze flows down the vessel. Variable Factors: Different woods yield different results. Hardwoods (oak, maple) generally produce more stable, glass-like finishes, while softwoods (pine, spruce) can be more aggressive in their melt. Local Clays and Slips Local "wild" clays are rarely pure. They often contain high percentages of iron, titanium, or manganese, which function as built-in colorants. Wild Clay Slips: Instead of using a commercial slip, creating a slip from local earth and applying it under a transparent glaze can produce variegated, earthy tones that reflect the local terroir. Clay as a Glaze Component: Adding 5–10% of a local clay to a standard glaze recipe can introduce "micro-crystals" or "speckling" that gives a handmade, rustic quality to the finish. Unconventional Colorants and Fluxes Once you are comfortable with the basic Glaze Composition and Chemistry, you can begin substituting standard oxides with non-traditional materials to achieve unique visual effects. Metal Scraps and Industrial Waste Some potters experiment with introducing small amounts of metal oxides found in industrial by-products. Caution: This is the highest-risk area of experimental glazing. Many industrial wastes contain heavy metals (like cadmium or …
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