Identifying What Your Pottery Will Be Used for Is the First Consideration When Choosing the Correct Glaze. Then you hear the glaze types – Matte Finish, Transparent, Translucent, Opaque., Underglaze, Overglaze, you can get confused and overwhelmed very quickly.
Glazes Are Not Just the Coatings That Give Your Pots Their Color and Texture. You will Need to Know What Type of Glaze Will Work Best for Your Projects Before You Start Glazing. Follow Along as I help you Learn How to Choose the correct Glaze for your next Pottery Making Project.
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The firing temperature of your kiln has the biggest impact on the glaze that you choose. You have three main types of glazes: low-fire pottery glazes, mid-fire pottery glazes, and high-fire pottery glazes.
What are Low fire glazes?
Low-fire glazes have the advantage in depth of color and use less energy to achieve the desired results. Most Potters use low-fire glazes at temperatures between 1828 degrees Fahrenheit (998 C) to 1945 degrees Fahrenheit (1063 C). Glazes like this usually have a bright and vibrant color. Also, low-fire glazes support a high gloss. The most popular range firing of Low-fire glazes is from Cone 04 to Cone 06.
One of the most common clays that you will use with low-fire glazes is the earthenware clay. This clay has a highly plastic (workable) body. Pay attention to the color of clay because that matters.
You may see an entirely unexpected color that you didn’t want. For example, you could apply a low-fire glaze to brown or red clay and get a different color than you anticipated.
What is a Mid Range Glaze?
The mid-range or mid-fire glaze is used on porcelain and stoneware clay. Stoneware is the most common mid-fire clay, but you do see it used for porcelain more and more. The mid-fire glaze temperatures range from 2167 degrees Fahrenheit (1186 C) to 2262 degrees Fahrenheit (1239 C).
Historically, potters used mid-fire and high-fire glazes for more earthy colors but are moving towards brighter colors also. An estimated 75 percent of potters use mid-fire glazes, according to Ceramics Monthly. Usually, mid-fire glazes range from Cone 5 to Cone 6.
Important to note: Low-fire, mid-fire, and high-fire glazes mature at varying temperatures.
Many Potters choose mid-fire glaze when you want the piece to have a practical purpose rather than decorative. Mid-fire glazes most often get used for functional purposes because they are more durable. The colors generally looked duller, but as technology has advanced, we have brighter mid-fire glazes.
What is High Fire Glaze?
High-fire glazes use Cone 8 to Cone 10. Most porcelain and stoneware use high-fire temperatures and high-fire glazes. Temperatures for high-fire glazes will range from 2280 degrees Fahrenheit (1249 C) to 2345 degrees Fahrenheit (1285 C). Similar to mid-fire glazes, the colors can look more muted and dulled, but the technologies of today have improved the color spectrum, like with mid-fire.
You might choose high-fire glazes if you wanted to seal and protect your ceramic piece from discoloration and moisture. High-fire glazes offer the most durability.
Why You Need to Choose the Right-Fire Glaze?
You need to choose the right-fire glaze because it can affect the glaze and ruin your ceramic work. That is another reason we recommend you try the glaze out on a test piece first to better understand how the glaze will get along with the clay to give you the desired result.
The most important factor is that the glaze works with your Choice of Clay. In other words, you need a low-fire glaze with low-fire clay and so on. Preference and artistic style does play a role, but this comes first.
With any glazes, whether high-fire, mid-fire, or low-fire, you should test them before you use them. This helps you account for kiln personality and fit with the glaze and clay. The glaze and clay need to expand and contract together.
You need to consider the Clay that you will use along with the glaze to avoid unexpected effects. There is a very good reason for making low, med, and high fire glazes. The fluxes that are added to the glazes make the silica and alumina melt at different temperatures. It’s always best to match the firing temperature of your glaze with the firing temperature of your clay.
Underfiring Glaze and Overfiring Glaze – What Happens When You Choose the Wrong Glaze?
Underfiring a glaze happens when you fire it to lower temperatures than intended. Because you underfired it, the glaze never reaches maturity. The underfired glaze will look harder, rougher, and drier than when you put it in the kiln. With severely underfired glazes, they won’t have a glossy or glassy appearance because they never reached the correct temperatures for them to vitrify. You can also run into problems like pinholes.
Luckily, you can normally re-fire an underfired pot at a higher temperature, which may salvage your ceramics.
On the other hand, you have overfired glazes, which happens when you fired up a glaze above the temperatures that they designed it for. Some potters overfire their glazes on purpose to grow crystals on them. If you have crazing happen, you can adjust it with silica, in most cases.
You don’t always have issues with overfiring glazes, but you can run into problems like the glaze running off your pottery. A beginner potter may experience problems if they overfire, so they may want to stick with the outlined temperatures.
What is the Kiln Firing process for Glaze?
The heat in the kiln will spark a chemical reaction that changes the appearance of the glaze. The ceramics in a gas kiln will look different from the ceramics in an electric kiln. Typically, gas kiln ceramics don’t have the bright and vibrant appearance as they do in an Electric Kiln.
Understanding how the kiln will have an impact on your glaze can influence the type of Kiln that you Choose. Electric kilns are more popular and considered to be neutral or oxidation kilns. Oxidation is a chemical reaction that removes the electrons from the substance. Whereas Gas kilns are Reduction that adds electrons to it. Gas kilns use a damper because they need oxygen to burn. As an experiment, you could partially close the damper, and it would have a new impact on the glazes. You get some brilliant glaze coloring effects with this extra tool at your disposal.
Gas kilns today don’t have nearly the popularity as electric kilns do. They take on a less vibrant appearance because of how the gas burns up the oxygen in the kiln, which influences its color. A gas kiln does tend to create a darker and more intense color in the glaze.
This reduction firing in most cases will melt the glazes faster. Many high-fire glazes even request reduction firing, so you should be aware of this before you choose a glaze. Never try reduction firing with an electric kiln since you can’t do this safely.
How to Choose a Pottery Glaze – Do You Need a Food-Safe Glaze?
Decorative glazes catch the eye with their vibrant colors, but eating off them could pose a danger. If you want to eat off a plate, choose a functional glaze.
How do you Test a Food Safety Glaze?
You have two tests that you can perform to see if your glaze is food-safe. Important to note, the two tests especially come in handy if you pulled a glaze recipe off the internet, but you don’t know you can use it for functional purposes.
While these tests can work, if they prove inconclusive, you will want to send the glazes to a lab to determine safety for eating off them.
You have the lemon test. To begin the test, you squeeze a lemon on a horizontal and glazed surface. You might perform this test before bed. Squeeze the juice and place the lemon over the juice for the night. Once you remove the lemon, you will wash away the juice, and if you see new discolorations, it indicates that you have a non-food-safe glaze. Choose another glaze for functional purposes. The lemon could leach other materials out of the fired glaze.
As you can imagine, you don’t want yourself or your customers eating food with an unsafe glaze on it.
Beware of the same issue with cups. We should highlight, however, that just because the glaze doesn’t leach into the lemon doesn’t mean that it doesn’t leach into the food. It simply means that it doesn’t leach badly. When in doubt, use a liner glaze around the areas where you would eat and save the questionable glazes for the exterior.
You can use the microwave test in coordination with the first test. You will take a test piece and microwave it after you filled it with water. If the surface didn’t vitrify properly, the clay body will absorb the water, and it will become extremely hot. When this happens, the water can form a questionable bond that interferes between the clay and the glaze. The thermal shock from hot water can cause it to chip the glaze. You may also see crazed matte on the outside and tight liner on the inside.
Specific types of glazes like metallic and lusters can spark a fire in the microwave. Don’t choose this glaze if you want to use it as a plate for food, even if you never plan to use it in the microwave—somebody else might.
You can find out more about how to use your pottery in the microwave by reading Is Pottery Microwave Safe
It’s always good to be aware of the purpose of the glazes that you choose. Do you have a food-safe glaze or a purely decorative glaze? Beware of anything that uses metallic finishing or trim. If you plan to Sell Pottery that is not food safe and may be used for food in some way, you want to include a warning label for customers.
Applying Glaze to Pottery
Maybe you just got started with glazing pottery. When choosing your glaze you can get a Matte finish or Shinny. When it comes to the selection of glazes it seems endless.
We would recommend that you start with brushing glazes. You can buy Brush-on Glazes in smaller quantities, and as the name implies, you brush it on. Some glazes allow for brushing, pouring, spraying, even dipping.
Brushing glazes include several advantages like being good for beginners, offering a broad range of colors, the ability to control the thickness. Read more on Brush Glazing Pottery to give you tips, tools, and ideas.
Beware of some brush glazing recipes that may contain lead, which can be dangerous to your health. Any glaze with a bright color may contain lead. The commercial bottles will often cost more than if you mixed your own but will indicate if they are lead-free.
With brushing glazes, you need Brushes that will hold the glaze.
Dipping glazes are mainly used as a single-layer base coat. Many potters choose the dipping glaze as a much faster way to glaze.
Dipping glazes have to be mixed often, but the advantage is the glaze dries faster, and you only need one dip as opposed to 3 or more layers of brush glazing. Yes, brush glazing takes longer, but dipping can be more one-dimensional.
For more information on how easy dip glazing can be check out What is Dip Glazing.
Why is it a Good Idea to Fire Glaze Test Pieces?
We always advise that you perform a test fire in pottery with your glazes because it gives you a real demonstration of what color it will look like. All glazes look different in liquid form than after you have fired them up in the kiln. In fact, that same glaze can even vary depending on the kiln you used and the firing temperature that you chose. Instead of thinking of this as intimidating, think of it as the ultimate creative freedom.
In some cases, potters have complained because they received a sample piece of what the glaze would look like when finished. Firing it up in their own kiln, however, the glaze looked completely different. With glazes, you should always expect the unexpected.
Should You Choose Liquid or Dry Glazes?
Most potters think of liquid glazes as more expensive than dry glazes because you need to mix dry glazes. In truth, dry glazes don’t differ that much in cost unless you buy it as a larger unit. Instead of looking at this based on cost, we would advise that you look at it like this—how did they formulate the glaze, and how will you apply it?
Manufacturers made liquid glazes for brushing, pouring, and spraying. Dry glazes are used more for dipping or spraying. It would be a huge mistake to buy liquid glazes if you wanted to use the dipping method. The thicker liquid glaze makes it difficult to apply the dipping method.
You can, in contrast, choose a dry glaze for brushing, but you would need to doctor it up a bit with a gum solution. Another thing to consider with liquid glazes is that they dry more slowly than dry glazes.
For someone who has never bought a dry glaze, they may want to try it at least once. It gives you the experience of mixing, sieving, and dipping the glaze. Dry glazes do have a cost advantage but not a significant one.
Liquid glazes are ready to use, and you can brush on many different colors and create cool patterns. Which is a nice advantage too.
Choosing to Make Your Own Glaze?
Instead of choosing a glaze, you can also make your own glaze, but we wouldn’t recommend it to a beginner. When it comes to your recipe, consider the following:
- What temperature will you fire the glaze at?
- Will you fire in reduction or oxidation atmospheres?
- Do you want a matte or glossy finish?
- What color do you want?
- Will the glaze be functional or decorative?
Glazes with a food-safe intention should be made within limit formulas. The limit formula makes the glaze safer for foods. You control the silica, alumina, and fluxes within limits.
The main ingredients to make glazes don’t cost much, you can make your own glaze with Quartz, feldspar(flux), and China clay which are used heavily by the average potter, so you might buy them in a larger quantity.
When to Choose Breaking Glazes
Think of breaking glazes as the type of glaze that creates a decorative effect. Breaking glazes will exploit the changes in color as well as when the thickness increases. This creates a beautiful contrast when done well, but you should choose a breaking glaze with the type of clay in mind. For example, some breaking glazes will look great with red clay, but they won’t look so hot on white clay.
When done correctly, it will emphasize the color. Breaking glazes should create a beautifully varied surface when you do it correctly. On raised contours, a breaking glaze will thin and highlight the surface.
Choose a Flowing Glaze?
Flowing glazes will move as you heat them in the kiln. You have two types of glazes here: Stable glazes, which remain in place, and flowing or floating glazes. A flowing glaze makes sense when you want to create an effect that looks the same as ash-glazed pottery. The ash glaze effect has historically been used in Japanese, Chinese and Korean pottery. Many traditionalist East Asian potters still use the ash glaze effect.
Flowing glaze sends rivulets of glaze flowing down your pottery. The advantage of a flowing glaze comes from how you can create this effect while using flowing glazes. Many flowing glazes require mid-fire temperatures but there are still low fire glazes that flow. This effect is created by the amount of flux used in the glaze. You can even buy Flux for mid-fire glazes to create this look. Each piece will have its own personality because the glaze movement differs with each piece. Some may see that as a disadvantage because they can’t control how it looks.
You might choose a clear glaze when you want to seal the ceramic piece to make it non-porous and food safe. Several varying degrees of clearness exist with clear glazes. Clear glazes are formulated for Low, Mid, and High fire clays.
Different ways to Decorate with Clear Glazes
A clear coat of glaze can be applied over the finish, which will protect it. Glaze also offers a way for you to personalize your work. The most common choices include:
- Colored slips
Now, let’s cover each of them and show you when to choose them:
You would use Underglazes when you want to create designs and patterns to come up through the glaze. It adds visual depth and character to your ceramic pieces from under the glaze. Underglazes can be applied under the most transparent or lighter-colored glazes. Because of the frit in underglazes, you can apply it to both your greenware at any stage and bisque ware. I do both with no problems.
Underglazing can be a whole new and interesting experience to the art of pottery crafting. To learn more about it, read Underglazing Pottery | Tips Tools and Ideas
How do you use Overglazes and Lusters
Overglaze does exactly as it sounds where you would apply the overglaze over the piece that already has a glazed and fired surface. Many potters describe overglaze as enameled decoration because the colors fuse with the glaze. You choose overglazes when you want to add accents to your ceramic piece.
Lusters act as a type of overglaze that you would apply over vitrified or a glaze-fired ceramic. Previously, we talked about lusters being a metallic glaze that isn’t microwave-friendly. Some potters have said lusters can be food-safe, but they don’t offer the durability required. You can get lusters in a variety of finishes that include platinum, gold, silver, and mother of pearl. If you choose a luster glaze, you should wear a respirator because this glaze has toxic fumes in its liquid form.
When you choose lusters, you need to consider the surface properties because this glaze takes on the qualities of the surface. If you have a matte surface, it will become matte, or if shiny, you will have a shiny surface. You can use lusters on ceramics and glass.
Overglazes and Lusters are fired at low temperature, Cone 018 or 020.
Colored Slips and Stains
Colored slips can color your ceramics without the higher cost. Many times, Pottery Classrooms will use colored slips because they don’t cost as much as underglazes. Most often, hobbyist potters also choose this one because of its fraction of the cost.
To learn more about making colored slips check out this article I wrote on How to Make Clay Slip for Decorating It also has a Step by Step Video for added instruction.
Stains come in the form of minerals like oxides and colorants like mason stains. Just mix with a little or a lot of water and start creating. Then cover with a clear glaze to make them food safe, shinny, or matt if like. Stains are fun to work with. You can apply them thick or thin. Even apply them thick and wipe some off for a cool effect.
Lead or Lead-Free Glaze
Having a brilliant and glossy surface, lead glazes will often exhibit vibrant colors. Unfortunately, they come with health implications if you swallow or inhale the dust fumes. For that reason, we would advise that you use a respirator when you work with lead glazes. You must use precaution when mixing, applying, and firing the glazes. When possible, you may want to use lead-free glazes instead.
You can tell that your ceramic piece has lead in it when it has the following signs:
- The decoration feels rough or raised
- Feel the decoration when you rub finger over the dish
- You see the brush stroked above the pottery
- Dusty or chalky gray residue on the glaze after washing
Choosing a pottery glaze comes down to understanding the appropriate times where you would use them. Outside of personal preference, each glaze has a point in time where it makes the most sense to apply it. You also have times where you can’t use a certain type of glaze because it doesn’t fit your ceramic piece. For example, it doesn’t make much sense to use low-fire glaze on porcelain because of how this clay requires mid-fire to high-fire glaze. You need to understand where each glaze applies, and we hope that we have highlighted the uses so that you can learn when to choose the glaze.