If you’ve ever attended a weekly pottery class, chances are the glazing process felt a little like a mystery. You might have been shown how to wax the bottom of your pot, dip it into a bucket of glaze, and place it carefully on a kiln shelf — without much explanation of what’s actually happening inside that glaze bucket or during the firing itself. For many studio potters and hobbyists, glazes remain one of the most elusive and underexplored areas of ceramics.

And yet, glazing is one of the most rewarding areas of study in ceramics. It’s where science meets art, and where a little knowledge about glaze chemistry and firing dynamics can unlock whole new creative possibilities. Whether you’re interested in classic celadons, rich iron tenmokus or silky matte finishes, understanding how glazes work is essential to developing your own style and achieving consistent, beautiful results.

At Corrie Bain International Ceramics School, we’re passionate about helping potters develop confidence in this area, which is why we’re running a glaze workshop in Barcelona this winter with John Britt, a studio potter and glazing expert. In this article, we’ll share a beginner-friendly overview of how glazes work, look at common types of glaze, and explore some of the chemical changes that occur during firing.

What is a ceramic glaze?

First things first – what exactly is glaze? Essentially, it’s a thin layer of glass that melts and bonds to the surface of a ceramic piece when fired. Beyond its obvious decorative appeal, glaze makes your pottery waterproof, food safe, and more durable. It also transforms the surface visually and tactually — from glossy and reflective to matte and velvety, or from opaque to transparent.

A basic glaze recipe typically includes:

Silica (the glass former)
Fluxes (which help the silica melt at lower temperatures)
Alumina (to stabilise the melt and control glaze flow)
Colourants (such as oxides of copper, cobalt, or iron)
Opacifiers (like tin oxide, zirconium sillicate, or titanium dioxide for creating opaque finishes)

When heated in a kiln, these ingredients go through a series of chemical reactions, melting and fusing into a continuous glassy surface. The exact temperature range for this to happen depends on the clay body, the glaze composition and the type of firing.

What are the different types of glazes?

While there are endless recipes and variations, most glazes fall into a few broad families based on appearance and composition:

Glossy glazes: Bright, glass-like finishes that enhance colour and surface details.
Matte glazes: Soft, non-reflective surfaces, often achieved by adjusting alumina or silica content.
Celadons: Transparent glazes tinted with small amounts of iron oxide, typically pale green to blue, with beautiful pooling effects.
Tenmokus: High-iron glazes, usually dark brown to black with red or amber highlights.
Ash glazes: Traditionally made with wood ash, which creates flowing, variegated surfaces.
Salt glazes: Produced by introducing salt into the kiln during firing, resulting in a distinctive orange-peel texture.

Understanding these categories helps you choose and adjust glazes for your own work, depending on the look and texture you want to achieve. We’ll go into more detail on the variety of glazes available in the John Britt masterclass, discuss how and why each type of glaze works and how you can achieve them. We’ll also explore how to adjust your glazes and how to find new ones.

Common glaze application techniques

In our ceramic studio in Barcelona, we have a variety of glazes available to our pottery students. How you apply each glaze affects both the finish you’ll achieve and how it interacts with your clay body. Popular techniques include:

Dipping: Quick and even coverage, ideal for production work.
Pouring: Great for large pieces or layering glazes.
Brushing: Perfect for detail work or textured surfaces.
Spraying: Allows for delicate colour gradients and even layering.

Different glazes require different dipping times. Some glazes can’t be sprayed because impurities or large particle size of the raw materials in the glaze can either block or wear out the nozzle of the spray gun. Some can be layered whereas others don’t work so well in this way. On our weekly pottery courses in Barcelona, your teacher will be available to guide you through the glazing process.

The firing process: what happens in the kiln?

So you’ve waxed the bottom of your piece and dipped, poured, brushed or sprayed glaze on to the bisqued surface – but what happens when your pot goes into the kiln? When a glazed pot is fired, it undergoes a transformation that’s both physical and chemical. As the kiln temperature rises:

The clay body continues to vitrify (harden and partially melt).
The glaze ingredients begin to decompose and react.
Silica melts, and fluxes lower the temperature at which it can do so.
Colourants develop their final hue depending on temperature, atmosphere (oxidation or reduction), and glaze chemistry.

The final result depends on multiple factors, not just the glaze recipe, but also on the clay body type, wall thickness, shape of the form, surface texture, how fast the kiln heats up, how long it holds at peak temperature, and how it cools down. That’s why, in our glaze workshop in Barcelona, we’ll discuss firing dynamics — so you can better predict and control your glaze outcomes.

Troubleshooting glaze problems

Even experienced potters encounter glazing issues. Some of the most common problems we discuss in our glaze workshop Barcelona include:

Crazing: Fine cracks in the glaze surface due to mismatched expansion between glaze and clay.
Pinholing: Tiny holes from trapped gases or dust.
Running: Over-fluxed glazes that melt too much and slide off the pot.
Blistering: Bubbles formed by gases escaping during the firing.

Understanding the causes of these faults helps you troubleshoot and adjust your recipes or firing schedules accordingly.

Join our upcoming glaze workshop in Barcelona with John Britt

If you’re ready to go deeper into the world of glazing, sign ups have opened for our glaze workshop with John Britt in November. This workshop offers a comprehensive overview of ceramic glazes, with a particular focus on (but not limited to) cone 6 glazes.

Designed for beginner to intermediate potters, the course will cover:

Cones, kilns, and firing dynamics
Principles of glaze formulation and adjustment
Classifications of glazes like ash, celadon, temmoku, and more
How and why each glaze type works
How to tweak existing glazes and discover new ones
Insights from John’s latest book The Complete Guide to Mid-Range Glazes: Glazing and Firing at Cone 4–7, with expanded, workshop-exclusive detail

Whether you’re a studio potter or an ambitious hobbyist, this is an incredible opportunity to demystify glazing and gain hands-on, practical knowledge from one of the world’s leading glaze specialists.

Places are limited, so apply for a place on our glaze workshop Barcelona with John Britt.