introduction: why is drying clay completely before the first firing so crucial?
working with clay is an art that combines creativity and technical know-how. one of the crucial steps in this process is allowing the clay to dry completely before the first firing. this stage is often overlooked by beginners, but it holds immense importance for several reasons.
why let clay air dry?
preventing cracks and explosions: moisture trapped inside clay can lead to cracks or even explosions in the kiln. as the water turns to steam, it expands and needs a way out. if the clay is not thoroughly dry, this expansion can cause severe damage to the piece.
structural integrity: properly dried clay has better structural integrity. it can withstand the high temperatures of the kiln without deforming, ensuring that the final product retains its desired shape.
even firing: uniform drying contributes to even firing. when the moisture content is consistent throughout the piece, it reduces the risk of uneven shrinkage and warping, resulting in a more uniform and predictable final product.
time and energy efficiency: dry clay fires more efficiently, saving time and energy. wet clay takes longer to reach the desired temperature, increasing both the firing time and energy consumption.
glaze adherence: dry clay provides a better surface for glaze application. glazes adhere more evenly on dry surfaces, enhancing the aesthetics and durability of the final glazed piece.
the drying process
slow and even drying: the drying process should be slow and even to prevent warping and cracking.
materials: this can be achieved by covering the piece with a cloth or plastic sheet and gradually exposing it to air. if you have paint-free, leftover drop cloth from a painting project, or recycled pieces of plastic such as grocery bags or dry cleaning bags, you can use these to cover your pieces. grocery bags work well for smaller pieces they can cover completely, and dry cleaning bags work well for larger pieces.
placement: make sure that there are no holes in your plastic where it is covering the piece to ensure uniform drying. drape the plastic completely over the piece. if you make a bowl and find that the rim dries more quickly than the interior, you can rip a hole in the center where the interior is, leaving the rim covered and the interior exposed. if you "scratched and attached" elements to your pottery, as you would do with a handle on a cup, it is important to thoroughly wrap the new attachments with the piece to mitigate cracking at the attachment site. I will cover the "scratch and attach" method in a later post.
checking the dryness: to check if the clay is dry, you can touch it. if it feels cold, it's likely still retaining moisture.
thorough drying for thick pieces: thicker pieces require more time to dry completely. ensure that the center of the piece is as dry as the surface before firing.
extra: not required, but a magnificent way of keeping your pottery from drying out too quickly is a damp box like this one found at The Clay Plant, inspired by Danny Meisinger. they built their own but with a little know-how and the room to do it, you could make your own for your pottery studio. if woodwork is not your thing, you can also buy one, or make a simplified version yourself.
air dry clay at different rates: porcelain vs. stoneware
an important aspect of the drying process in pottery is recognizing that different clay bodies dry at varying rates. this variance is crucial to understand for achieving optimal results and avoiding common issues like warping or cracking.
porcelain: the delicate dancer
porcelain often requires a longer drying time. this is due to its dense nature, which slows down the evaporation of moisture. porcelain's delicate composition also means it is more susceptible to damage if dried too quickly. for instance, rapid drying can cause porcelain to crack, as the outer layer shrinks faster than the inside. therefore, patience is key when working with porcelain – a slow, consistent drying process allows for a more uniform moisture reduction, ensuring the integrity of the final piece.
something I have found helpful during the winter in my at-home studio is a good humidifier. I like to let my covered porcelain dry as slowly as possible, and I have found that adding a humidifier to the process further mitigates cracking in the drying process.
stoneware: the robust contender
in contrast, stoneware, with its coarser grain and more robust nature, tends to dry more quickly than porcelain. this is due to its more porous composition, which allows water to escape faster. however, this doesn't mean stoneware is immune to drying issues. uneven drying can still lead to problems, especially in thicker pieces. monitoring the drying process and ensuring even air exposure can help mitigate these risks. stoneware's quicker drying rate is often advantageous, allowing for a more efficient turnaround from creation to firing.
balancing act
understanding these differences is crucial for potters. while porcelain requires a gentle, patient approach, stoneware calls for a vigilant, yet slightly quicker process. both, however, demand a keen eye for even drying. adjusting your drying techniques to accommodate the specific characteristics of your clay body can make a significant difference in the quality of your final product.
greenware, or bisqueware?
at times, when we're juggling multiple pottery projects simultaneously, it can be challenging to keep track of each piece's progress. This can lead to confusion: Is the pottery completely dry and prepared for its initial firing, or has it already undergone the first firing and is now ready for glazing and the second firing?
both stages are critical in pottery, but they have distinct characteristics and purposes.
dried, un-bisqued clay: the preliminary stage (aka greenware)
dried un-bisqued clay, often referred to as 'greenware,' is clay that has been shaped and allowed to dry completely, but has not yet been fired in a kiln.
key identifiers
color and texture: it typically retains the color of the wet clay, though slightly lighter. the surface feels dry to the touch but can be easily scratched or dented.
strength and fragility: this form of clay is very fragile. while it can be handled, it's prone to breaking or crumbling if not treated gently.
sound: when tapped, it produces a dull, solid sound, lacking the resonance of fired clay. I like to use a metal pin tool to lightly tap on my clay if I need to double-check its stage in the process.
moisture sensitivity: dried, un-bisqued clay is still susceptible to water. if it gets wet, it can soften or lose its shape.
bisque fired clay: the transformation
bisque firing is the process of firing clay in the kiln for the first time. this transforms the clay into a hard, durable material.
key identifiers
color change: bisque-fired clay usually changes color, becoming whiter or more earth-toned, depending on the clay body.
texture: the surface feels harder and smoother compared to greenware. it cannot be scratched easily with a fingernail.
sound: when tapped, bisque ware produces a distinctive ringing sound, indicating that the clay has been vitrified and transformed. again, best to use a metal pin tool for this step to get the ringing sound.
water resistance: unlike greenware, bisque-fired clay doesn’t soften or disintegrate with water exposure. however, it remains porous and can absorb water. it is important not to soak your biqsued clay prior to glazing it, or else the glaze will not adhere properly. I will cover glazing in a later post.
understanding these differences is crucial for potters. the transition from dried, un-bisqued clay to bisque-fired clay marks a significant change in the material's properties, affecting how it should be handled, stored, and further processed (like glazing). recognizing these stages ensures proper treatment and avoids common mishaps in pottery making. a common default suggestion in a pottery studio is to repair broken pottery with the Japanese art form of repair, Kintsugi. this can yield beautiful results if done correctly and would be done after the glaze firing, but ideally, you want to create a piece without cracks in the first place.
conclusion
in conclusion, drying clay thoroughly before the first firing is not just a step in the process; it's a safeguard against failure and a practice that ensures the quality and longevity of the ceramic piece. by respecting this crucial phase, potters can achieve better results and mitigate unnecessary setbacks.