As a beginner, I am sure you have had quite a bitter-sweet experience when it comes to pottery. I am certain you have your terrible experiences and the most adorable experiences. The centering process the molding process, the glazing process or even the firing process will have been a challenge to you in one way or another. The most important thing is that you see those challenges as a way of getting better in pottery. You don’t allow the setbacks to weigh you down rather you build on it. Speaking of setbacks, I am going to be talking on one of the major problems you have encountered or likely to encounter and how to prevent them. Today, I am going to be talking about Pottery Explosions in the Kiln.
If your pottery has not exploded before, then you are lucky, if yours has, then you are luckier. Pottery happens to everyone especially beginners. A piece of dinnerware or ceramic blows up, sending ceramic shards flying around everywhere. You’re fortunate if the explosion doesn’t take down other pieces in the kiln.
WHY DOES A POTTERY PIECE EXPLODE?
I am sure this is your most anticipated question. Do not worry, I will break it down to you.
1. Too much Moisture in your piece
A lot of research has been made and they all concluded that water is the reason why most pottery pieces will explode. A moist project is prone to explosion when it is being heated up. At 212°F degrees and higher, the water turns into steam. The pressure from the steam, and nowhere for it to escape, causes the piece to explode. If there’s too much moisture in your artwork, especially moisture inside hollow air pockets within the clay, you run the risk of having your artwork explode. This is one of the reasons I keep pacing emphasis on drying your ceramics thoroughly before placing them in the kiln.
2. Firing the Kiln Too Fast
As an amateur, you will be so eager to get your pottery piece baked so you can take pictures of it or probably sell it. There is no problem with that; I believe every piece of pottery you make is an achievement and it is meant to be celebrated. Just because you are eager does not mean you should rush things or skip a process. A few professional potters have attested to the fact that firing the kiln too fast may make your pottery explode. Firing the kiln at full speed or too fast is unsafe. Potters want to fire their kilns faster to save time and energy; but little did they know that fast-firing causes more damages than any other firing practice. Shortly, I will describe the problems that can arise at each firing stage when the kiln is fired too fast.
KILN FIRING STAGES
- First Stage: Water Smoking
It is obvious that all clays contain elements of water. This first stage of firing is done to burn off the water in ceramic. As the water heats, the ceramic expands and it is being pushed out of the clay. This is known as water smoking. Fast firing during this stage can lead to disaster. If the kiln temperature passes the boiling point of water (212°F), the water in the clay will expand too quickly. During water smoking, it is advisable to keep the kiln switches turned low. If you are using a pyrometer or digitally controlled kiln, it is best to maintain the temperature at 200°F or lower.
- Second Stage: Dehydration
After the first stage, your artwork continues to lose water but at a molecular level. This continues to about 1100°F. At this Dehydration stage, your piece changes chemically into fired ware. At around 1060°F, the clay goes through what is called quart inversion, which is the point at which the silica in your piece expands. During the dehydration stage, the molecular water will leave the clay slowly, especially if the pieces are large. At this stage, the clay will break if heated too quickly.
- Third Stage: Oxidation
Right from the very beginning of firing (water-smoking stage), impurities burn out of the clay from the, but most of the impurities burn out during the Oxidation stage. This is one of the reasons why venting the kiln is so important at the beginning of firing. The piece must be heated slowly and steadily to give impurities, such as carbon, enough time to turn into gases and combine with oxygen. The heavier the ware and the heftier the load, the slower the piece must be fired.
- Fourth Stage: Maturity
This is the crucial stage where the heat has transformed the ware to the degree intended by the potter. As stated in previous articles, over-glazes mature at 1000° – 1500°F; low-fire stoneware ceramics mature slightly over 1900°F; and porcelain and high-fire stoneware ceramics mature at 2100° – 2400°F. Be sure of the recommended firing temperature of your clay so as not to exceed the temperature.
|WATER SMOKING||200°F or lower|
|OXIDATION||1100°F – 1300°F|
|MATURITY||1900°F – 2400°F|
3. Improper Wedging of your pottery
Another major cause of potter explosion is improperly wedging. When you don’t wedge your clay in the correct ways, it will leave air pockets in your piece thereby making it prone to explosion when being heated up. As a newbie in pottery, you should pay special attention to your wedging process and make sure you don’t leave air pockets in your piece.
HOW TO PREVENT YOUR POTTERY FROM EXPLODING IN THE KILN?
- Air Dry your pieces:
One way to avoid your piece from being moist when it is about to journey its way into the kiln is by air-dying to be as dry as possible. One way to find out if your piece is completely dried out is by putting the ware up to your cheek. If it is colder than room temperature, it has too much moisture in it, allow it dry for longer. Or you can place your project on a piece of paper. If the paper wrinkles, there is too much moisture trapped in the piece. Let it dry.
- Create a hole for steam to escape
Build holes around your piece to allow the steam to escape. A hollow piece without a hole can become a grenade in the kiln. While the clay is super hard, use a needle to make small holes on the piece. The holes should not be too big but it should be large enough for steam to escape when being fired.
- Fire using long Preheat
Preheat is the first stage of the firing process. Preheat is also known as water-smoking. Most electric kilns can be set to a temperature of 180°-200°F for a programmable amount of time to allow moisture to evaporate from the piece before the kiln heats up past 212°F.
- Fire Slow
If your kiln is not a programmable one, my advice will be for you to fire your ware slowly. If you are not sure about how dry a piece is you can fire slowly to make sure all the moisture in the piece evaporates properly. You should consult your manual for the slowest programmable speed. If you are using an older version kiln, you can start with the kiln on low temperature for 4 hours, medium temp for 3 hours and then you can switch to high temp until the cone melts.
To make firing easy and comfortable, and to prevent your pottery from exploding, it will be best for you to get your personal kiln. Using a community or public kiln may put your pottery in the risk of explosion. You can get your electric kiln from amazon by clicking here.
I know an exploded pottery piece can be frustrating. But after reading why pottery explosions happen and how you can prevent them, you can reduce the chances of your pottery exploding.