You've just finished a pottery piece – maybe a bowl, a vase, your first mug – and now it sits before you, waiting. The question almost all beginners ask at some point is: How long does this need to dry before I can put it in the kiln? And can't I speed that up somehow?
If you're wondering instead whether you can fire clay in a normal oven, then this article is relevant for you: Can you fire clay in a normal oven?
This post is written by Formwerk Berlin Pottery Supplies.
The short answer
As a general guideline, you can remember: Small, thin-walled pieces need at least 3 to 7 days under normal conditions. Medium-sized vessels like cups or bowls typically need 1 to 2 weeks. Thick-walled or complex pieces can easily take 2 to 4 weeks or more.
However: these numbers are guidelines, not guarantees. What matters is not how many days have passed, but whether the clay is truly bone dry. You'll learn what that means and how to recognize it further down.
What happens in the clay during drying?
To understand why drying is so important, a quick look at the material helps. Fresh clay from the package contains between 15 and 25 percent water, depending on the type. This water makes the clay plastic and moldable – without water, no pottery. At the same time, it keeps the tiny clay particles apart from each other.
During drying, the water evaporates gradually. The clay particles move closer together, and the clay shrinks. This is visible: your piece becomes noticeably smaller. Drying shrinkage ranges from 2 to 8 percent, depending on the clay type; together with firing shrinkage, total shrinkage is 6 to 15 percent. This sounds like little, but it is quite relevant when measuring.
There are also completely air-drying clays, such as Witgert Airdry 191,
The real problem arises if there is still water in the clay when the piece goes into the kiln. Above about 100 °C, water turns into steam. Steam needs considerably more space than liquid water. If the steam is trapped within a dense clay body and cannot escape quickly enough, it builds up pressure – and the piece cracks or explodes. In the worst case, this happens explosively, which not only destroys your own piece but also all other pieces in the kiln and, in extreme cases, can even damage the heating element.
Important to know: Even a piece that looks dry and light on the outside can still contain residual moisture inside – especially with thicker wall sections. You cannot rely on the exterior alone.
The three drying stages you should know
Clay goes through three clearly recognizable phases during drying. Knowing them means you always know where your piece is – and what is possible at that moment.
① Plastic / soft
Immediately after forming
- Dark color, feels cool to the touch
- Malleable, but unstable without support
- Attach handles only at the same moisture level
② Leather hard
Ideal for finishing
- Lighter color, still slightly cool
- Firm, but no longer cracking when worked
- Trimming, incising decoration, attaching handles
③ Bone dry
Only now can the piece go into the kiln!
- Uniformly light color, rings hollow when tapped
- Cheek test: feels body warm
- Weight loss approx. 15–20% compared to fresh
Drying Time Guidelines
| Thin-walled piece (up to 4 mm) | 3–7 days |
| Cup / Bowl (5–8 mm) | 1–2 weeks |
| Large vessel / Jug (up to 12 mm) | 2–3 weeks |
| Sculpture / Solid form | 3–6 weeks |
Explanation of Stage 1: Plastic / fresh
Freshly formed clay is malleable, moist, and deeply dark in color. Water is available at full concentration. The piece feels cool because evaporation is already occurring on the surface. In this stage, the clay can still be pulled, pushed, and joined. Do not touch without support, or the piece will immediately deform.
Important: When joining elements – such as attaching a handle – both parts should have the same moisture content. If you join a soft, fresh handle to an already-dried body, both parts will shrink differently, and the handle will crack off during drying.
Explanation of Stage 2: Leather hard
You typically reach the leather-hard state after about 2 to 8 hours in the air – depending on room temperature, humidity, and wall thickness. The clay has gained stability, is firm, but still moist enough not to crack when worked mechanically.
This is the best stage for trimming (finishing the bottom of a vessel on the wheel), smoothing surfaces, incising decorations, or attaching handles. Leather hard to leather hard provides the strongest connections. The piece still feels slightly cooler than room temperature and has a slightly lighter color than fresh, but not yet a uniformly light hue.
Explanation of Stage 3: Bone dry
Bone dry means: all free, evaporable water has left the piece. The clay no longer shrinks. It is uniformly light, lightweight, and sounds hollow when tapped. It is also brittle – be careful when loading it into the kiln. Only in this state can a piece go into the kiln.
Important to note: Even a bone-dry piece still contains chemically bound water, which is deeply embedded in the crystal structure of the clay minerals. This chemically bound water only escapes in the kiln at temperatures between approximately 200 and 600 °C. It no longer causes steam explosions – however, a slow heating rate during bisque firing is still important in this temperature range.
The most important factors influencing drying time
The exact drying time cannot be answered with a single number. Too many variables play a role. The most important ones are:
A) Wall thickness is the strongest single factor. Double the wall thickness roughly means four to six times longer drying time internally. As a guideline: wall thicknesses over 1 cm are generally not needed for normal utility ceramics. Compact, solid forms like sculptures must be hollowed out and need an air hole so that steam can escape during later firing.
B) Humidity in the room has an enormous influence. In a damp cellar or on a foggy autumn day, drying takes considerably longer than in a heated, dry room. If possible, dry your pieces where the air is driest.
C) Room temperature helps. Warmer air absorbs more moisture. At 22 °C, clay dries faster than at 16 °C. But: do not place your piece directly next to a heater – this leads to uneven drying and cracks.
D) Air movement is a double-edged sword. Slight air circulation in the room accelerates drying. Strong drafts or a fan blowing directly on the piece will cause edges and thin areas to dry much faster than the core areas – this creates tension and cracks.
E) Clay type also plays a role. Coarse grog stoneware clay dries slower but evenly and with fewer cracks. Fine earthenware clay dries faster but is more sensitive to drafts. Porcelain is the most demanding candidate: it shrinks significantly, tends to develop drying cracks, and requires particular patience and generally slow drying under loosely draped plastic.
A plastic base, as shown above, is practical but can block even drying from below.
F) Surface is often forgotten. A plastic base blocks drying from below – the bottom remains moist while the walls dry and shrink, leading to classic cracks at the wall-base junction. Better: unprinted paper, a wooden board, or a plaster bat, which absorb moisture and allow for even drying. Also, turn pieces regularly – every 1 to 2 days – so that the bottom can dry as well.
Guidelines: How many days for which piece?
The following figures apply to normal room temperature (approx. 20 °C) and medium humidity (50–60 %). In more humid rooms or with thicker-walled pieces, always calculate more generously.
Drying Time Guidelines
At approx. 20 °C and 50–60% humidity. In more humid rooms or with thicker walls, calculate more generously.
Incidentally, bone-dry pieces can be stored for any length of time – provided they are kept dry, frost-free, and safe from being knocked over. So you don't have to fire immediately if your kiln isn't full yet. Wait until you have a reasonable load. This saves energy and protects the kiln.
How to tell if your clay is truly bone dry
Don't just look at the calendar days – let your clay speak. There are several reliable methods:
The cheek test is the most reliable. Hold the piece briefly against your cheek or the inside of your wrist. Does it feel cooler than your skin? Then there's still moisture in the clay – evaporating moisture draws heat from the surface. Does it feel body-warm or neutral? Then the clay is bone dry.
The color test: Bone-dry clay has a uniformly light, almost dull color – without darker spots or areas indicating still-moist zones. Feel free to compare it with a sample of the same clay type that is demonstrably dry.
The tap test: Gently tap the piece with a knuckle or fingernail. Bone-dry clay sounds bright and hollow. Moist clay sounds dull and muted.
The weight test: Weigh the piece when forming it and again when you consider it finished. Bone-dry means the clay has lost about 15 to 20 percent of its original weight. For larger pieces, this is easily measurable – sometimes it's a 50g difference for a normal mug.
When in doubt: Wait another two to three days. Drying too long won't harm it. Drying too short will destroy the piece.
Even drying: Why most cracks are avoidable
Most drying cracks occur not because the piece was dried too briefly, but because it was dried too unevenly. If one side of the piece dries and shrinks quickly while the other is still moist, tension builds up in the material. Eventually, something gives way – usually at the thinnest point, a joint, or the edge between the base and the wall.
Drying crack on the mug handle, highly likely to fall off
The most common sources of error are: direct sunlight (one side dries much faster), drafts or a fan directly on the piece (edges dry first), a plastic base (the bottom stays moist), very different wall thicknesses within a single piece, and joints like handles attached with the wrong moisture level.
The solution for complex shapes is the plastic sheeting technique: Loosely drape a plastic sheet over the piece. The sheeting slows down drying and equalizes moisture differences between wall areas, the base, and attached parts. Every other day, briefly lift the sheet, turn the piece over and air it out for a short time, then cover it again. This way, even a complicated piece dries almost crack-free.
What happens if you fire too early anyway?
For completeness – so you know what's at stake. At approximately 100 °C in the kiln, the free water begins to evaporate. If there is still a lot of moisture present, more steam is generated than can escape through the pores. The internal pressure rises until the piece cracks or explodes. This often happens in the first hour of firing, sometimes later.
From approximately 200 to 600 °C, chemically bound water leaves the clay. This process also occurs in bone-dry pieces – which is why a slow initial ramp in the bisque firing is always recommended. With modern kilns featuring programmable controllers like the Bentrup TC66, used in many Pyrotec and Kittec kilns, this heating ramp can be precisely set. Typically, 60 to 100 °C per hour is common in the initial phase. A selection of suitable controllers can be found here: Controllers for Pyrotec kilns and Bentrup controllers for Kittec kilns.
With advanced controllers like the Bentrup TC66, heating ramps can be precisely adjusted.
Special considerations for different clay types
Coarse grogged stoneware clay dries slowly but very evenly. The added grog particles prevent cracks from spreading quickly. If you are building large formats or potting sculptures, a grogged clay is significantly better than fine, highly plastic mass.
Fine earthenware clay has high plasticity and dries relatively quickly, but is more sensitive to drafts and uneven support. Porcelain is the most demanding candidate: it shrinks significantly, tends to develop drying cracks, warps easily, and generally requires very slow drying under plastic sheeting, away from temperature fluctuations and drafts.
Can drying be accelerated?
The short answer: Yes, with limitations – and only for simple shapes without joints. A slightly elevated room temperature (25–28 °C) significantly accelerates drying without creating significantly more risk of cracks, provided the air is not too dry and the piece is uncomplicated.
What definitely doesn't work: Quickly drying pieces with a heat gun. The surface closes and dries, while moisture is still trapped inside. In the kiln, the piece then explodes with almost predictable reliability.
Conclusion
The crucial question is not "How many days?", but: "Is my piece really bone dry?" The days on the calendar are a guide, not a free pass. Use the cheek test, look at the color, tap the piece. And if you're unsure – it's better to wait a few more days. A cracked or exploded piece costs far more time than two weeks of patience.
Anyone who wants to fire regularly also needs a reliable kiln with a programmable controller that allows for a gentle initial ramp. In our shop, you'll find a carefully selected range of kilns from Kittec and Pyrotec: Formwerk Berlin – Kilns.
PS: In 2026, you'll receive a 5% discount on all kilns in our store with the code WELCOME5. Simply enter it at checkout, and the discount will be applied directly to the purchase price.
The Formwerk Berlin Team wishes you much success with drying and good firings