So why is porcelain often less forgiving than stoneware? When you’re using porcelain for the first time, a pot that seems solid a few minutes earlier might start to sag, or a thin edge might lose its line, and a slight change in moisture might change how two parts fit together. This doesn’t mean that porcelain isn’t suitable for beginners, it just means that porcelain tells you when something changes with your pressure, moisture, wall thickness, or time. You’re better off learning how to recognize the signs of changing conditions than trying to get porcelain to act like a heavier clay body.
Porcelain tends to have a lower tolerance for inconsistent treatment. Porcelain’s fine texture and high kaolin content lead to nice smooth finishes and good fired results, but porcelain can be less plastic than many stoneware clay bodies. Adding more water to help it form might result in a softer surface than the rest of the piece, and if you apply more pressure afterward, you’ll find that you’re stretching one part more than another. Rather than reaching for a sponge every time you hit resistance, compare the reaction of the clay before and after a tiny bit of moisture.
At this point, the thickness of your walls is going to matter. Create two small cylinders using roughly equal preparations of porcelain. Leave one relatively uniform, and make the second one thicker towards the bottom or on one side. Smooth both with a flexible rib without pushing too hard. When these are no longer soft greenware, look at whether either has started to lean, and if the rim of either starts to pull in or out as it dries. This will show you why wall thickness needs to be consistent long before a piece is bisque fired.
Even the drying process can expose issues you hadn’t noticed while making the piece. Thin edges dry faster than thick bases, so those parts will shrink at different rates. If the edges dry while the body stays wet, that might contribute to deformation or a crack as the two sides pull apart. Wrapping a freshly made piece lightly and letting it dry slowly will give you more time to watch what the porcelain is doing. Check in on the piece regularly, don’t assume that if it hasn’t changed appearance, the moisture is still the same throughout the piece.
Joining two pieces can add another variable. If the handle is very soft and the cup body is very firm, or you add a small piece onto a form that is already too stiff to work with, they will shrink at different rates as they dry. Scoring and slipping are necessary, but matching the moisture level of the pieces and applying gentle pressure are equally important. Make several small joined pieces at slightly different points of firmness, label them, and dry them under the same conditions. You’ll be able to see which seam is strongest. This will teach you a lot about timing and joinability.
Porcelain also benefits from being handled with care when it comes to decoration. Rubbing the edge of a piece over and over with a wet sponge or scraping the same spot over and over will damage the piece, rather than improve its finish. Trimming and smoothing tend to be easier once the piece has reached leather hard, because it can take more pressure. Later on, using test tiles lets you experiment with underglazes, slips, and glazes at varying thicknesses without needing to apply each one to a larger pot.
This brings us back to the question of whether or not porcelain is more challenging than stoneware. There’s no way to say that all clay bodies react the same way in all circumstances; every clay body has a different optimal use. With porcelain, try to monitor three things every time you notice a change in your pot: Where is the moisture going? Is the wall thickness uniform? How much pressure am I putting on it? Once you know what to look for before a piece goes into the kiln, porcelain will seem much less unpredictable.