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For many years I focussed on sculpture, and I cast most of those pieces in plaster rather than firing them. And when I started to make pottery again, I wondered, how long does it take for pottery clay to dry? So, I did a bit of research and a lot of trial and error, this is what I found out.
Potters often say it takes about 7 days for pottery clay to be dry enough to fire. However, other factors affect the length of the drying process. These factors include how thick or large the piece is, how complex the design is and what the drying environment is like.
Clay goes through different stages in the drying process. At each different stage, it has particular qualities and can be handled in different ways.
This article will cover the following:
- How long do the different stages in the drying process take?
- What are the factors that affect how quickly pottery clay dries?
- How to help pottery dry without cracking and how this affects the drying time?
How Long Does it Take for Clay to Dry? – The Different Stages
Plastic Workable Clay
The rule of thumb is that clay will stay in its plastic workable state for between 15 and 30 minutes.
When clay is in its plastic workable state, it contains around 30% water. It is soft and pliable, but it is not sticky to touch. If it leaves a sticky mess on your hands, it is too wet. If this is the case, leave it to sit for a little while until it is not sticky.
I would recommend leaving it with a plastic bag placed very loosely over it. This will stop it from drying too quickly but will allow enough air to circulate. It may take a few minutes or up to an hour for the clay to be less sticky.
When clay is out in the open air, it stays in its plastic, workable state for a short period of time. If you are using the clay to model or sculpt, it stays workable for 15-30 minutes. After that, it will start to lose enough water that it stops being quite so plastic.
When you are throwing clay on the wheel, you will need to drip water on your clay regularly to keep it slippy and workable.
How Long Does it Take for Clay to Become Leather Hard?
On average it will take around 1-3 days for clay to become leather hard. However, this does depend on how you are storing and drying it.
Leather hard clay is a bit paler than the clay in its plastic state. It is dry to the touch, but it feels cold. This is because it still has relatively high water content.
In its leather-hard state, clay is brittle and will crumble if pressure is applied to it. If you leave leather hard clay on an absorbent surface, like a paper towel, it will leave a damp patch.
How Long Does it Take Pottery Clay to Become Bone Dry?
It is generally said that clay can take up to 7 days to become bone dry.
When clay is bone dry, it is pale and feels warm and dry to the touch. To prevent your ware from exploding in the kiln, it needs to be bone dry before it is fired.
Some potters will put clay in the kiln when it is a little damp. But if you do this, it needs to go a long pre-heat of around 12 hours. During a preheat the kiln needs to stay below 212F, so the water evaporates off before the firing schedule starts.
A Rule of Thumb Guide for Drying Out Clay is as follows:
| Plastic Clay | Leather Hard Clay | Bone Dry Clay |
|---|---|---|
| 15-30 minutes | 1-3 Days | Up to 7 Days |
If you are itching to fire your ware, then the above guidelines may feel frustratingly vague. However, it is possible to gauge more accurately how long your particular piece will take to dry. You just need to take into consideration the following factors….
How Long Does it Take Pottery Clay to Dry? -Different Factors
How Humid Is the Environment?
Clay takes longer to dry out if it is in a humid atmosphere. This is something to consider if you live in a humid climate, or it is a humid season.
As a potter, you can control how humid the air is around your clay. Plastic can help you control humidity levels. Potters with a nice big studio can section off part of their workspace using plastic drapes or space dividers.
However, you can control the humidity in the air around your clay by covering it with a plastic bag. If you do use a plastic bag, it may be a good idea to cover your greenware with fabric first.
As the moisture in the clay slowly evaporates, it will produce condensation. This will settle on the surface of the bag. If the bag then clings to the greenware, it can erase details on the surface of your piece. Or it can make parts of the clay softer and wetter than others.
Some potters recommend covering the piece with paper towels. Others recommend a piece of soft cloth or fabric that will drape over the piece gently. This will absorb the condensation, and stop the plastic from clinging to your clay.
You can also create something called a damp box. A simple version of a damp box is to place a plastic bucket over your piece. This controls the humidity in the atmosphere around your piece and stops draughts from getting at the clay. As such, it gives you some control over how long it takes for the pottery clay to dry.
Here is my step-by-step guide on how to build a damp box for clay.
How Much Does Humidity Affect Drying Time?
The following will give you an idea of how humidity affects drying time2. Ware sealed in a bag OR put in a damp box uncovered may be leather hard in 1-3 days.
If sealed in a bag AND put in put in a sealed box, ware may be leather hard in around 5 days.
A moisture source like a wet sponge can be introduced to the environment. When added to a sealed bag the clay can stay workable for weeks. Clay in a damp box can stay workable indefinitely.
Thick or Large Clay Pieces Take Longer to Dry
As the clay dries, water needs to migrate from the deeper levels of clay to the surface. The larger or thicker the clay, the further it has to travel and the more water that needs to evaporate.
Even when clay is bone dry there will still be some residual water content. And there will be water chemically bonded to the clay particles too.
It may be tempting to try to speed the drying process up with thicker or larger pieces. Different potters have their own ways of escalating the drying process.
However, it is very important that greenware dries at a consistent rate. As much as possible, it is best to avoid one part of the clay drying out quicker than another.
If one part of the clay dries quicker than another, a “drying gradient3” is set up. When this happens the clay body undergoes a lot of stress. One part of the clay is shrinking faster than the other, and the piece can crack as a result.
Some potters argue that if you put greenware in the sun it can be leather hard in less than an hour1. Others2 argue that you can only dry clay in the sun if it has a high grog content. Grogged clay does not shrink so much. However, plastic clay will shrink too quickly in the sun and you risk your ware cracking.
This last point leads me to the next factor that affects the drying rate. Namely, the kind of clay that you are using. So, read on….
What Clay are You Using? – Drying Performance
Different clay bodies have a different ‘drying performance4’. This refers to how able the clay is to shrink without cracking. If the clay has a poor drying performance, then you will need to take longer drying the clay out. Drying performance is, therefore, a factor in how long it takes for pottery clay to dry.
Plastic Clay
If clay is very plastic it tends to shrink more when it dries. If clay shrinks unevenly it tends to crack. Drying clay out evenly tends to take longer. Therefore, clay with high plasticity needs to be dried out more carefully. And can take more preparation and time.
Grogged Clay
Grogged clay dries more easily because it is less plastic. Therefore, it doesn’t need to be treated so carefully. For example, heavily grogged clay can be left to dry in the sun with much less chance of cracking.
Porcelain
Porcelain loses water very quickly when it is drying. The fact that it loses water fast would suggest that it takes less time to be ready for firing. However, because it loses a lot of water quickly, porcelain also shrinks a lot, and is prone to cracking.
As a result, the drying process has to be managed quite carefully. The potter is advised to dry porcelain out slowly to avoid cracks coming from rapid shrinking.
How to Help Pottery Dry Without Cracking – a Stitch in Time
Sometimes we are in a rush and we want our pottery to dry out fast. Perhaps you have a deadline to meet for a customer or a gift for a friend. You may tapping your fingers wondering, how long does it take for pottery clay to dry? And you may want to speed the drying process along.
Some potters say that this is a no-no, and that most methods of speeding up drying are a mistake5. Others argue that you can accelerate how long it takes to dry pottery clay as long it dries evenly6.
Some Ways to Speed up the Drying Process
Some of these tips may seem like they are slowing down the drying process. However, by ensuring that your clay dries evenly, you avoid cracks and potentially having to start again. A stitch in time, as they say!
- Make your pieces with thinner walls, these will dry quicker.
- Try to ensure that the piece is of even thickness throughout.
- Make sure that pieces of clay are joined together well. If they are joined poorly, they may crack as the piece dries. If they are joined well, you can dry your piece more quickly with less risk.
- You can put your piece in front of a fan, heat gun, or hairdryer. If you do this, it’s a good idea to put your piece on a slowly rotating surface like a slowly rotating wheelhead. This will ensure that the clay dries evenly.
- When you are able to pick up the piece without damaging it, turn it over. This ensures that the underside is also exposed to air.
Covering your ware
- Put your pots on shelves, or a grid to dry. This lets air flow around the whole of the piece freely. You can loosely cover the piece with plastic to manage the speed at which it dries.
- Cover those parts of the ware that will dry out too quickly. Handles on cups and lips of pots dry out quicker.
- It is a good idea to cover edges and details to slow their drying down. You can cover them by wrapping them in plastic or using wax resist.
- Remember if you use wax resist to leave a thin strip of unwaxed surface. This allows moisture to escape. This may seem like it is slowing the drying process down. However, if you protect the vulnerable, exposed bits, you can leave the larger areas to dry out more quickly.
- If you are making a batch of mugs, dry them in a circle with the handles pointing towards each other. Then cover the batch. This creates a humid environment for the handles to dry out.
- You can place your piece on a plaster bat, cover it with fabric and seal it in a plastic bag. The plaster bat will draw water from the base which normally dries more slowly. And the moisture in the bag stops the overall piece from drying out too quickly. A piece can become leather hard in 24 hours using this method.
Pre heating your pottery
- You can put a less than bone dry piece of ware on a long preheat in the kiln. Some potters will do an overnight preheat at less than 212F (100C). This ensures the clay is bone dry before the firing schedule begins. I find that pre-heating for around 3 hours at 194F (90C) is enough to ensure that my pots are completely dry.
- Some potters have a more homespun approach and put their ware in the oven for a stint at 200F.
These tips are largely aimed at speeding up the drying process. But it is important to remember that pottery requires patience. Sometimes you just need to give time time.
Final Thoughts How Long it Takes For Clay to Dry
These are ballpark figure answers to the question of how long does it take for pottery clay to dry. The actual drying time depends on the factors outlined in the above article. The drying process can be accelerated if it is done carefully and the clay dries out evenly. Equally, if the clay is kept humid, the drying process can be delayed indefinitely.
References.
1) https://sites.google.com/site/devicemanlessons/storingclay
2, 3, 4 & 6) Digitalfire.com
5) https://www.thesprucecrafts.com/drying-pottery-and-clay-objects-2746236