Change 1 – Drying out Residual Moisture As mentioned above, before the clay is bisque fired, it's important that it is dried out thoroughly. Clay going into the kiln needs to be bone dry, which means that it's as dry as it can be. If clay goes into the kiln damp, it can break or explode when it is being fired.
If your pottery is not bone dry before firing, there is a higher chance of cracking or even breaking in the kiln. The more you know about the drying process, the less likely you will have cracks.
Once your pottery has been designed and formed, it is vital that it is completely dry before firing. Failure to do so can compromise the end result, causing the pottery to become frail, cracked or even breaking once in the kiln.
As clay heats up the kiln, any moisture in the clay evaporates and expands rapidly. If there are small air pockets in the clay, the expanding steam goes into the gaps. This puts stress on the clay and can cause it to break or sometimes explode.
When a piece is not completely dry and is put into the bisque kiln it will most likely explode and/or crack. Water (or the moisture in the clay) when heated will expand and turn into vapor, causing the piece to make way for the expansion of the moisture and explode.
This is ideal as you don't need to worry about having to work fast – you can take your time sculpting the clay before setting it aside to dry. Air-dry clay takes between 24-48 hours to dry, depending on the brand or size of the project. Smaller air dry clay projects will dry much quicker than larger projects.
Drying the Clay
It is very important to make sure the clay is completely dry before you place it in the kiln. Water turns to steam at 202 °F. if there is still moisture in the clay in can actually explode the piece as the steam tries to escape.
Underbaked clay is not only less flexible, it is susceptible to breaking and crumbling. Underbaked polymer clay can also have excess free plasticizer that can lead to cure inhibition in paints and glues, causing them to remain soft and/or sticky.
With a larger kiln, you can often find yourself waiting to fire the kiln because you do not have a full load. You can usually fill a small kiln, and if it's really important you can afford to fire a partial load so you and your customer both win.
If you use low fire clay and it melts and ruins the kiln furniture or kiln. If you drop off work that is thicker than 1/2” thick. Know that I candle for only 2 hours, so if your work is overly thick it is at risk. Our target market is ¼ ” - ½ ” thick.
After you've made your pot from clay it will be ready for its bisque firing once it gets to the bone dry stage (about 1 week after the making of it). Your pot needs to be bone dry to go into the kiln for the first firing to prevent it from exploding!
Most pottery is fired twice (or in some cases 3 or more time!). The first firing is called the bisque, then there is a second firing for the glaze.
If the clay pieces begin to dry out, place them in a resealable bag and spray them with some water. Seal the bag and wait a few hours. The clay should be ready to use.
Without firing the clay, it really has very little strength and a short life span. We do not recommend using greenware as your final piece of artwork or a base for painting because even if you could get the paint to stick, it would not add protection or strength.
Kiln bricks are also made of ceramic and find continual sharp changes in temperature stressful. They can crack as a result of these abrupt shifts. In addition to this, opening your kiln lid too early can also shorten the life expectancy of your elements.
The sudden escape of heat and the introduction of cool Air into Your Kiln can cause the pottery to crack or tiny fractures to appear on your glazed pottery, a process called “crazing.” Because the clay and glaze expand and contract together during the firing, if the glaze cools too fast it may contract around the clay ...
There are several reasons that you may want to fire a kiln at night: Sometimes you can get cheaper electrical rates. Often, there is not a voltage drop at night in areas where power conditions are not great. Sometimes you need to if the cycle is too long for you to be near the kiln the whole time.
Yes, you can bake a piece more than once. You can bake a piece of clay as many times as you need to get a complete cure. So, if you've accidentally underbaked your clay, you can bake it again.
Generally speaking, no, Clay will not expire as it ages. However, Clay does dry out over time. Clay meant for kiln firing won't go bad. In cases where the Clay became too Hard and dry to work with, add water to the Clay and wedge it out.
Polymer clay that's too supple is challenging to work with and may stick to everything — or everything sticks to it! It may even clog your pasta machine when you're trying to condition it.
Dry clay is also known as 'greenware'. It is when clay is at its most fragile, and needs careful handling to prevent breakages. Dry clay needs to be fired in the kiln in order to make it strong enough to use. Use: Any sharp edges that are not smoothed at this stage will become solid in the bisque firing.
The strength of fired clay is increased by the formation of new crystalline growth within the clay body, particularly the growth of mullite crystals. Mullite is an aluminum silicate characterized by a long needlelike crystal. These lace the structure together, giving it cohesion and strength.
Vitrification can be obvious by simple visual inspection
Together they produce this dense, almost zero-porosity ceramic. The unglazed surface on the right looks more like plaster, and it is absorbent, about 5% porosity.