The pottery-making process can feel like an endless number of steps towards your finished piece. This can lead an enthusiastic beginner to ask, do you have to bisque fire pottery? Is bisque firing essential, or can you miss out this step in the firing process?
The two-step firing process, with a bisque fire followed by a glaze fire, is common practice. However, it is not essential to do a separate bisque fire. Either pottery can be left unglazed. Or you can use a technique called raw-glazing. This involves applying glaze to unfired greenware pottery.
If you have looked into whether you have to bisque fire pottery, you may have read about single-fire glazing. Single-fire glazing eliminates the need for the bisque step because the pottery is only fired once. This can be confusing for some beginners. This article is to help you decide on what you want to do with your pottery.
Do You Have to Bisque Fire Pottery? – An Overview
Most pottery goes through a two-step firing process. First, a bisque firing, then it is fired again to melt the glaze. It’s a two-step process, although the second firing is optional.
During a bisque fire, the clay undergoes important chemical and physical changes. Residual moisture evaporates from the clay. Water that is bonded to the clay at a chemical level is driven out. And organic materials in the clay body burn away.
In addition to this, the surface of the clay particles start to adhere to one another. And the clay particles move closer to one another. The clay becomes harder and denser. This process is known as sintering, and this is the point at which the clay becomes ceramic.
Before a bisque fire, bone-dry clay can easily be rehydrated and made workable again. Once it has become ceramic, it can no longer return to a pliable state. Ceramic bisque-fired clay is porous but insoluble.
A bisque firing also prepares the pottery for glazing. The porous quality of some bisque-fired clay makes it perfect for glazing, as it absorbs liquid well. Glaze adheres to the bisque surface because the porous ceramic absorbs the water in which the glaze materials are suspended.
More often than not, the glazed ceramic is then fired a second time. The second firing is also known as the glaze fire or ‘glost’ fire. During this firing, the glaze melts and forms a glass layer over the surface of the pottery. This can look lovely and it often makes the pottery impermeable.
However, the two-step glazing process is not the only option. You can make a choice whether to fire your pottery once or twice. Both methods have their own pros and cons.
Do You Have to Bisque Fire Pottery? – Single Firing
As the name suggests, single firing eliminates the second firing step. Single fired pieces are similar to bisque fired pottery, because the greenware is fired one time. However, single-fired pieces are often glazed in their greenware state.
If you prefer to make your piece all at once, instead of in stages, then this method may appeal to you.
Potters have been doing single firing for many years. Many historic pieces were made this way. The two-step firing process was not discovered until much later.
Using the kiln once saves time and money, by firing and glazing in one go. However, the risk of cracked or damaged pottery increases when glaze is applied to raw greenware. It’s helpful to know your glazes.
Raw-Glazing for a Single Fire
Applying glaze to greenware before bisque firing is called raw-glazing. It requires certain types of glazes, preferably those with high clay content.
Raw-glazing is similar to the underglaze process, in the sense that glaze is applied to the clay prior to firing. Most underglaze can be applied to clay at any greenware stage, either before or after the bisque firing. Here are some tips and techniques on using underglaze on your pottery.
Experienced potters can create their own glaze and make adjustments to increase the clay content to make it compatible with single-firing.
Shiny glazes are not ideal to use for single firing, because they usually have a lower clay content. You will probably have better results with matte or semi-gloss glazes.
Methods of Raw Glazing
Some potters glaze the inside of the greenware when it is leather-hard. They then wait until the outside is bone dry before glazing the outer surface. Others may glaze the whole piece. It’s okay to only glaze one surface. It really depends on your preference.
Glazes can be poured, sprayed, brushed, or layered, but it’s important to try and decrease the amount of water absorbed by the clay.
The first time I dipped greenware into glaze, I pulled it out and waited for it to fall apart, but it didn’t. Another time, when I tried the same approach it wasn’t quite so successful. The bowl did lose some of its shape. I think it was because I left it in the glaze too long.
Through trial and error, I found that most methods worked as long as the water absorption is minimal.
Keep in mind that there is a risk of flaking and cracking with single-firing. This is because gas bubbles will be escaping the clay as it heats up. Especially if the glaze doesn’t bond well.
For this reason, potters may prefer to apply glaze when the entire clay piece is bone dry and porous.
You can try the spray-glaze method for single fire pottery since it minimizes the amount of water being absorbed. Adding Gum Arabic to the glaze can help it to stick to the surface of greenware (source).
It’s good practice to experiment with different glazes and methods. Not everything will work out as you intended, but it’s the best way to find out what works for you.
Two Step Firing
The two-step firing method is the most common technique for pottery students to learn. The fact that it’s so common can leave new potters wondering, do you have to bisque fire pottery first?
In this approach, the first fire, or bisque fire, is followed by a separate glaze or glost fire. When clay goes into the kiln for a bisque fire, it is bone dry. However, in spite of looking completely dry, it does still contain some moisture. During the bisque fire, moisture and gases are driven out of the clay.
By bisque firing the clay first, the risk of damage to the pottery decreases. Partly because bisque pottery is stronger than raw greenware. But also, a lot of the impurities have already been burnt out of the clay. Because they have been removed, they no longer disrupt the glaze as it melts onto the ceramic surface.
In addition to this, glazes are easier to apply to bisque fired pottery. This is because you don’t have to worry about the bisque piece absorbing too much glaze and coming apart.
Do You Have to Bisque Fire Pottery? – Tips for Single Firing
- For the most part, single firing should resemble a bisque firing.
- High clay content glaze works best. Be cautious if you apply the glaze all over your pottery, because the water content may affect the shape.
- Try to experiment with raw-glazing methods and see what you prefer. It may help to increase the percentage of clay. Once you are familiar with the glazes you will get a better idea of how they work.
- Make sure your pottery is bone dry before firing. Putting wet pottery into a kiln increases the chance of it cracking or exploding during the firing process.
- Increase the temperature in your kiln, slowly. This is called the temperature ramp. Ramping up slowly allows moisture and gases to escape the pottery at a safer rate. This reduces the chances of cracking or exploding.
- If you’re single firing your pottery, you may need to fire it longer than if you were glaze firing too.
- Let the pottery cool (often overnight) before removing it from the kiln.
It’s helpful to know your glazes since not all glazes are compatible with raw glazing. High clay-content glazes are usually effective. You can experiment with different glazes and methods to see which works best for you.
In this article, I answered the common question many beginners have, “Do you have to bisque fire pottery?” In short, the two-step firing method is the most popular method of firing clay. Bisque firing gives you more options regarding the glaze you can use. However, kilns are not cheap to run. Therefore single firing pottery is an option if you want to save a little time and money.