Understanding glazes: types, application & common mistakes

Summary

• Understanding glaze types
• Glaze application in practice
• Insider knowledge from the workshop
• Typical errors & warning signs
• Checklist: Glazing safely
• FAQ
• Read more

In ceramics, glazes are what give a piece its finishing touch, both visually and functionally. Despite this, glazing is often underestimated or even dreaded by many. Beginners, in particular, are often surprised by how meticulous the work must be: a small mistake during glazing can ruin an otherwise beautiful piece. In practice, it turns out that glazing involves a great deal of knowledge that isn't readily available in the first Google results. This article puts the topic into perspective, dispels some misconceptions, and explains, based on experience, what really matters.

Why is this topic so crucial? If you regularly glaze your ceramic pieces, you'll quickly realize that glaze isn't just decorative; it also affects the stability and everyday usability of your pottery. Many hobby potters initially think glaze is simply "paint" that can be applied as desired. But experienced potters know that glazing is a science in itself. It's about choosing the right glaze for the right clay, using the appropriate application technique, and avoiding pitfalls that only become apparent after years of experience. This article aims to help you with exactly that – with practical insider knowledge instead of dry theory.

Understanding glaze types

Not all glazes are created equal. Depending on the type of clay, firing temperature, and desired effect, there are different types of glazes. In workshops, it's often apparent that beginners lose track of the options. So, what types of glazes are there, and what do they mean for you?

Low fire, high fire & temperature ranges

A fundamental difference lies in the firing range of the glaze. Low-firing glazes (e.g., for earthenware, usually around 1020–1150 °C, roughly equivalent to clay with a firing range up to cone 04/03) melt earlier and often produce vibrant colors. High-firing glazes (for stoneware/porcelain, around 1220–1300 °C, cone 6–10) require more heat but are usually more robust and food-safe. What does this mean in practice? If you have an earthenware clay (potter's clay for around 1060 °C), you cannot glaze it with a stoneware glaze (which only melts properly at 1250 °C) at a low temperature; the glaze will remain dull and rough. Conversely, a low-firing glaze will run or lose its color at stoneware temperatures. Many experienced potters report that incorrect temperature combinations are one of the most common mistakes beginners make.

A common misconception is that you can use any glaze on any clay as long as the temperature is right. In practice, however, you'll find that the clay and glaze must also be compatible in terms of their coefficient of thermal expansion. If the glaze isn't suitable for the clay, fine cracks will appear in the glaze after firing (craquelure), or in the worst case, the glaze will shatter and break off from the ceramic (shivering). Something you only realize after years of experience: professional ceramicists pay meticulous attention to such "glaze-clay compatibility." For hobbyists, this means: use glazes that are recommended for your specific clay and firing temperature range.

Transparent, opaque and effect glazes

Besides the firing range, glazes also differ in their appearance and composition. There are transparent glazes that act like a see-through coating. These are ideal when the clay or underglaze painting should remain visible. Opaque glazes, on the other hand, cover completely; they often contain tin or titanium to create opacity. Many beginners wonder why, for example, a white glaze sometimes appears translucent and sometimes opaque. The thickness of the glaze layer plays a role here. In practice, it turns out that transparent glazes often shouldn't be applied too thickly, otherwise they appear milky or crack during cooling (stress cracks). Opaque glazes are a bit more forgiving, but can obscure details on the surface if they are applied too thickly.

Then there's the world of effect glazes : crackle glazes (which intentionally form fine cracks), flowing glazes that run in a controlled manner, or glazes with a crystal effect. Such glazes can produce wonderful results, but are tricky to use. Something you won't find in any beginner's book: these special glazes often require precise firing curves (e.g., slow cooling for crystal glazes) and a lot of testing. Experienced ceramicists advise trying such experiments on test pieces first and approaching them step by step, rather than immediately glazing your favorite piece with them.

Ready-made glazes vs. homemade glaze mixes

During your pottery journey, you might consider making your own glazes from raw materials. Ready-made glazes (from brands like BOTZ, AMACO, or Mayco) are convenient and ideal for beginners. They come pre-mixed, often in liquid form, and are quite reliable in terms of color and melting point. Many hobby potters swear by these brands because they offer quick results. However, if you work regularly, you'll eventually realize that you might be looking for specific effects or want to save money on larger quantities. Mixing your own glaze recipes requires knowledge, and yes, you learn primarily through trial and error. Forums often discuss whether mixing your own glazes is worthwhile. The honest, practical answer: For more advanced potters who have their own kiln and find the chemistry behind it fascinating, it can be worthwhile. You then have complete control over color, effect, and firing behavior. But be warned: Testing your own glazes also means potentially producing a whole kiln full of rejects until you get the result you want. For beginners and anyone who simply wants beautiful pieces, ready-made glazes are a blessing. Feel free to use them extensively before venturing into the witch's kitchen of glaze mixtures.

Glaze application in practice

Now for the practical part: How do you apply the glaze to the piece? This is often where the wheat is separated from the chaff. Many think they can simply grab a brush and get started. However, in the workshop, it quickly becomes clear: The application method and preparation determine success or frustration. Let's go through a few tried-and-tested techniques and tricks step by step.

Preparation: Clean and absorbent shards

Before any glaze is applied to your piece, the bisque (the fired, unglazed piece) must be prepared. "Dust is the enemy of glaze": This is something experienced potters often say. In practice, this means that after the bisque firing (the first firing), your piece has a porous surface and may have dust particles or fingerprints on it. The best way to remove dust is to wipe the surface with a slightly damp sponge. Caution: not wet, just mist. If the piece absorbs too much water, it will be less receptive to the glaze, and the glaze will adhere less effectively. Many experienced potters even briefly refire their pieces ("flame-firing" them in the kiln) or blow them with compressed air to ensure they are clean.

There should also be no grease or oil on the piece. A common insider tip: until glazing, handle the bisque ware only with clean hands (or gloves). You wouldn't believe how a small grease stain can later cause a crater in the glaze. You'll notice such spots at the latest when glazing, because the glaze will run away from them as if by magic (glaze "creeps"). This is a warning sign: wipe it off immediately, clean it, and glaze again.

Stirring and consistency: Preparing the glaze

Standing glazes tend to separate. You've probably noticed this before: a thick layer of sludge at the bottom of the bucket, and relatively clear liquid on top. So, before each application: stir vigorously! In workshops, you'll see professionals using power drill mixers. At home, a strong arm and a clean stirring stick will do. Important: If dry glaze residue is stuck to the bottom or sides of the container, be suspicious. It's better to strain the glaze (pour it through a sieve), otherwise you'll have lumps that will create unsightly spots or bubbles during firing.

The correct consistency of the glaze is a crucial point that's rarely discussed. If the glaze is too thick, you'll quickly apply too much; if it's too thin, it won't provide adequate coverage. An experienced ceramicist would say, "It depends," because it varies depending on the glaze and desired effect. But for beginners, a good rule of thumb is: a consistency like low-fat milk is a good starting point. In practice, it's better to apply it a little too thinly and in two coats than too thickly in one coat and risk runs. If you want to be absolutely precise, you can measure the density (keyword: slip density or specific gravity). However, many hobby ceramicists forgo this step and learn to judge by eye over time. A good rule of thumb: when dipping, an even film should form, which becomes more matte within a few seconds (as the water is absorbed). If the surface remains wet and glossy for a long time, the glaze was too watery or the piece was too wet.

Methods: Dipping, pouring, brushing, spraying

Every application method has its advantages and disadvantages. Many beginners start with brush application because it seems the most obvious. However, it's important to know that ready-made glazes are often optimized for brushing (somewhat thicker and containing a binder to prevent running). Nevertheless, the rule is: apply brush-applied glaze in 2-3 thin coats instead of one thick one. Let each coat dry until it's matte before applying the next. Otherwise, you'll peel off the first coat (a common mistake among beginners).

Dipping is the fastest method for many pieces and results in an even coating. However, you need enough glaze in your bucket or bowl. In practice, you usually dip the piece completely for 1-3 seconds. Then, quickly but evenly, pull the piece out and let the excess glaze drip off. Advantage: It's quick and even. Disadvantage: It doesn't work for large pieces or if there's little glaze in the container. And be careful: Don't dip twice, otherwise the coating will become too thick. If you have areas that aren't well covered, it's best to touch them up with a brush.

Pouring is essentially dipping in stages: For example, you can glaze a large bowl by pouring glaze inside, swirling it around, and then pouring it back into the bucket. For the outside, you pour glaze over it from above and rotate the piece so that the glaze coats the entire surface. Many potters combine methods, such as pouring inside and dipping outside, depending on what's practical. Again, work quickly and don't let the piece "bathe" for too long, otherwise it will become waterlogged.

Spraying (with a spray gun or airbrush) is ideal for subtle color transitions or when working with many large pieces. Workshops often have spray booths for this purpose. The advantage: very even and thin layers that you can build up gradually. For example, you can first spray a base coat of glaze, then add accents with a second. The disadvantage: it's more technically demanding (equipment, compressor, protective mask due to the fine spray mist) and you lose a lot of glaze through overspray. For hobby ceramicists without the necessary equipment, this is usually not an option, but it's good to know that the method exists.

Inside, outside, and gravity

Perhaps you've already asked yourself: How do I glaze a vessel inside and out without letting it dry for hours in between? A simple but important tip: Always glaze the inside first, then the outside. Why? If you've poured glaze on the inside, the clay body becomes damp from the inside and needs some time to become receptive again. Many beginners make the mistake of immediately applying the glaze to the outside after glazing the inside. The result: The clay is so damp that the glaze applied to the outside barely soaks in and runs off. So, let the piece "breathe" for a few minutes (or longer with thick clay) before you glaze the second side. In the workshop, you often see experienced potters glazing several pieces simultaneously: first all the insides, then the outsides in turn.

Gravity is always at work during glazing: excess glaze wants to flow downwards. You'll notice this especially at edges and rims: the glaze is drawn away from the surface and collects as drops at the bottom edge. A common insider tip: run your finger or a sponge along the bottom edge immediately after glazing. This removes excess glaze and prevents most runs. Experienced ceramicists also like to briefly turn bowls and cups upside down after glazing to distribute the glaze more evenly before it dries.

The right time: Let it dry and check.

After glazing, let the piece dry. The glaze should be completely dry before the piece goes into the kiln. Use this time to inspect it: Are there any thin spots (where the clay body shows through)? If so, you can carefully dab on more glaze there. Do you see any drips or large runs? You can lift these off with a sharp knife or scraper when dry (carefully, so as not to remove the surrounding glaze layer). Many people also do the following: Once the glaze has dried, run your hand over the surface. This will reveal any unevenness or patches of powder (where the glaze didn't adhere at all) and allow you to correct them. You'll notice any remaining glaze on the bottom or surfaces of the kiln when you're putting the pieces away. Everything below the marked glaze line must be absolutely clean, otherwise you risk an unpleasant surprise on the kiln floor (fired ceramic pieces).

Interesting facts

There are things that hardly anyone talks about in pottery books, but which are part of everyday life in the workshop. Here are a few insights that one often only learns after years (and a few mishaps):

• Glaze color before firing vs. after firing: Don't be fooled! Many glazes look completely different before firing than after. A sky-blue glaze cream might be applied as a gray, inconspicuous layer and only reveal its brilliance in the kiln. What does that mean for you? If in doubt, make a note or stick a piece of the label on the bucket. In shared workshops, sometimes the bucket lid says "This glaze fires pink" because otherwise, you wouldn't know.
• Test tiles are invaluable: Many experienced potters swear by small test tiles made from the same clay, which are fired along with the actual pieces. This way, you can see how a glaze looks on your clay at your firing temperature without risking a large piece. Something you only realize after a few failed firings: Every kiln fires a little differently, and even store-bought glazes can vary slightly depending on the batch. So test whenever you're unsure.
• Mixing or layering glazes: In online communities, ceramicists actively exchange information about glaze combinations (e.g., glaze A over glaze B creates fantastic crater effects). This is exciting, but remember: not every glaze is compatible with every other. Layering glazes can lower the melting point – suddenly the combination might run, even though each glaze would be stable on its own. Practical tip: Always test combinations on a sample piece first and place it at the bottom of the kiln (if something runs, it won't drip onto the good pieces below).
• Safety rules for glazing: Something often forgotten in the hobby workshop: Glaze materials are raw materials such as quartz, metal oxides, etc. Inhaling glaze dust (when mixing powder or grinding glaze drops) is unhealthy. Therefore, in workshops, always wear a mask when it's dusty and wear gloves when working extensively with glaze (especially with shiny metallic or toxic oxides). Lead-based glazes are thankfully rare in the hobby sector today, but if you are working with older glazes: be careful, never use them on tableware unless you know exactly what you are doing.
• Write it down and document it: Professionals keep glaze diaries. Sounds excessive? Imagine you've finally discovered the perfect combination of glaze, layer thickness, and firing time after much trial and error. If you don't write it down, you'll regret it later because you might not be able to reproduce it exactly. At a minimum, note: which glaze (manufacturer, name, batch), how it was applied (e.g., two coats of paint, 5-second dip), which clay, which firing temperature/cone, and the result. This database of your experiences will be invaluable for years to come.

Typical errors & warning signs

Now we'll focus on the pitfalls that almost everyone stumbles into at some point. The important thing to remember is: everyone makes mistakes (just ask around in a pottery group about "glaze mishaps"—everyone will have something to contribute). Here are some common problems, their warning signs, and how to avoid them:

• Applying too thick a glaze: Warning signs even before firing: The glaze dries with cracks on the surface or forms shrinkage cracks and "islands" that peel off (glaze crawling) as it dries. After firing, you'll see possible runs, thick drips at the edge, or, in extreme cases, glaze that has melted onto the kiln floor. Solution: Mix the glaze thinner or apply it more thinly, remove (scrape off) the excess before firing, and always leave an unglazed edge at the bottom.
• Too thin or unevenly glazed: This is noticeable after firing: the color appears pale, the clay shows through in places, or the surface is rough and not completely melted. The cause is often that the glaze was applied too timidly or wasn't stirred thoroughly (some particles settle, making the mixture weaker). Tip: It's better to work in two thin coats (especially when brushing) and always mix the glaze well before application. If you notice that a piece is underglazed after firing, you can often apply another coat of glaze and fire it a second time.
• Dirt, dust, or grease on the piece: The worst-case scenario is having bare patches or fine craters after firing where the glaze didn't adhere. Dust causes these small open areas (similar to orange peel), while grease leaves entire areas unglazed. A warning sign before firing: The glaze pulls back from certain areas immediately after application, forming "clouds" or spots where the glaze doesn't stick. Remedy: Wash or sand immediately, clean, and reglaze. Prevention: See above – always clean thoroughly, and wear gloves if necessary.
• Inappropriate glaze for the clay or incorrect firing temperature: If the glaze isn't suitable for the clay, you might see a fine network of cracks on the glaze after firing (hairline cracks, craquelure). While this is sometimes a desired effect, it usually indicates that the glaze shrank more than the clay body during cooling. Conversely, the glaze can chip (especially at the edges) if it shrinks less than the clay – this is quite dangerous because sharp glass particles can break off. An incorrect temperature is indicated by the glaze either remaining dull and porous (underfired) or burning and fading (overfired, especially with colored glazes). When in doubt: follow the manufacturer's instructions and conduct your own small tests to determine the optimal temperature for your glaze.
• Glaze in the wrong place (kiln plate/capsule): Every potter has experienced this, or at least seen it: glaze dripping onto the kiln plate during firing, or the piece sticking to the kiln support. This happens when you forget to keep the base clean or glaze too close to the edge. Warning sign: glaze already hanging as a droplet at the bottom edge before firing. Remove it immediately! Always leave a small unglazed border at the bottom (usually ~3 mm or more depending on the glaze). If possible, use wax or masking tape to cover areas. And remember: it's better to wipe the base with a sponge too often than to risk a shelf full of "stuck" artwork.
• Premature cooling: Imagine the firing is complete and you can hardly wait. But be careful: If you open the kiln too soon, the temperature shock can cause cracking (dunting) or the glaze can develop stress cracks. Typical signs are suddenly appearing cracks or a ringing sound when you later touch the piece. Recommendation: Let the kiln cool down completely, ideally to below 100°C, before opening it. Even if it's difficult!

Checklist: Glazing safely

Especially if you're new to glazing, this checklist can help you remember everything important. Many of us forgot a step at the beginning – sometimes with unpleasant consequences. Go through the list before you start your next glaze firing:

• Clay and glaze compatible: Is the glaze suitable for the clay (firing range, expansion)? If unsure, always adhere to the recommended temperature range.
• The piece is clean and ready: Is the ceramic piece dust-free and grease-free after the bisque firing? A quick wipe with a damp sponge never hurts.
• Mix the glaze thoroughly: Stir or shake vigorously once (with the lid on!) and strain out any lumps. Leave no solid deposits at the bottom.
• Consistency checked: Does the glaze feel like liquid cream/milk? If too thick, add a little water and stir again. If too thin, let it stand uncovered longer or add a thickener (e.g., some dissolved bentonite).
• Application method chosen: dipping, brushing, pouring or spraying? Planned how to cover all surfaces (e.g., inside first, then outside)?
• Work thinly and evenly: Two thin coats are better than one thick one. When using a brush: Let each coat dry in between.
• Clean edges: Is the bottom edge (at least 2–3 mm) free of glaze? Wipe the base edge with a sponge, also check holes and the base. Was wax resist used beforehand, if necessary?
• Allow to dry: Let the glaze dry completely before putting it in the oven. No damp spots should be visible.
• Pre-firing inspection: Final check: Any drips, runs, or overlooked unglazed areas? Correct them now (scrape them off, repair them), don't get annoyed after the firing.
• Setting the oven correctly: Is the correct program or cone selected? If you are unsure about potential stresses, it's best to let it cool down a little longer.

FAQ

Can I glaze ceramics without firing them?

A true glaze always needs to be fired to melt and transform into a glass-like layer. If you want to glaze "without firing," we're actually talking about a cold glaze . Examples include acrylic lacquer, resin, or special coatings for air-drying ceramics. These may look glossy, but they are never as durable or food-safe as a fired glaze. Okay for decorative pieces, but a no-go for tableware. In short: no firing, no proper glaze.

Can I glaze unfired clay (single firing)?

Yes, there is the technique of single firing, where you glaze the leather-hard or dried clay directly and then fire it only once. However, this requires a lot of experience: the drying state must be perfect, and the bisque firing in the kiln must be handled extremely carefully to prevent the piece from cracking. Many hobby artists prefer a bisque firing followed by a glaze firing because it simply yields more reliable results. If you don't have access to bisque firing (e.g., in a shared studio with limited availability), ask about glazes and clay types specifically suited for this method. But be aware: the risk of mistakes is higher with single firing.

Why does my glaze look dull or matte when it should be glossy?

If a glaze that should be glossy turns out matte, there are a few possible reasons. Either the glaze was too thin (in which case the glassy layer is simply missing), or the temperature wasn't high enough, meaning the glaze didn't melt completely. Another reason could be that you used an unsuitable glaze on unsuitable clay, or that the kiln was opened too early and a cold shock ruined it. In practice, this often happens with transparent glazes: if they're applied too thickly, they can appear milky and matte. Solution: Apply a thicker layer next time (if it was too thin) or fire at a higher temperature; if it was too thick, work with a thinner layer next time.

What can I do if the glaze has defects after firing (e.g., needles, cracks)?

Glaze defects are annoying, but sometimes repairable. Pinholes (small pinprick holes) can be fixed with a second firing: lightly sand the area, apply another thin coat of glaze if necessary, and fire again at a slightly higher temperature. Hairline cracks (craquelure) are unfortunately almost impossible to repair. This is usually a problem with the glaze and clay bonding. If it's a decorative piece, the cracks are only visually distracting; however, they pose a problem for tableware (hygiene!). Chipped glaze on edges can perhaps be smoothed, allowing the piece to be used as decoration, but it's usually beyond repair for everyday use. The bitter truth from experience: not every failed glaze can be salvaged. Learn from it, make a note of what went wrong, and try again.

What is the best way to store opened glazes or powder glazes?

Liquid glazes in tins or buckets should be tightly sealed after use to prevent them from drying out. If they do thicken, you can carefully add a little water and stir very well (but don't overdo it; too much water will ruin the recipe). Powder glazes prefer dry conditions: store them in an airtight container to prevent lumps from forming. And very importantly: label everything clearly! There's nothing more annoying than not knowing later which mysterious bucket of gray powder contained which glaze.

Read more

If you've become fascinated by glazes, there's so much more to discover. Here are a few further articles and resources in our ceramics universe: