How long does it take for the clay to dry?

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Clay is an ancestral material that hides many secrets for those who want to master it. From the moment it is extracted from the earth until it becomes a piece of pottery, it goes through several stages. But, undoubtedly, one of the most intriguing is drying.

We explain what you need to know to calculate how long it takes for clay to dry, what it depends on and the process involved.

How long it takes for clay to dry: clarifying the matter

Drying clay is not simply leaving it in the open air and waiting. It is a process that requires attention and care. If you’ve ever tried to model anything with clay, you know that if it dries too fast, it can crack. On the other hand, if it dries too slowly, it can develop mold. Therefore, it is essential to know the proper techniques for drying clay evenly.

Many ceramists often state that it takes approximately 7 days for ceramic clay to reach the required level of dryness before it can be subjected to the firing process. However, this period can vary significantly depending on a number of factors that influence the speed of drying, such as the thickness or size of the piece, and the environmental conditions in which it is found (temperature and humidity).

Defining the material:

First of all clarify that in this post I will talk about the natural clay used in ceramics, understood as clay. There are other materials such as paste or air-drying clay that are different and the term can lead to confusion if we talk about drying times, the latter material dries in the air and does not need firing, that is, it is NOT ceramic. On the other hand, we have polymer clay, which is a synthetic material based on polymers, which also does not form ceramics.

How clay dries

Clay goes through several stages during its drying process, and each of these stages has particular characteristics that allow for different manipulations.

At the beginning of working, a piece usually contains up to 35% water, which is dispersed throughout its mass, forming “capillary channels”, it is soft and moldable, but not sticky to the touch.

Tip: If you notice that the clay is too wet and sticky, you can let it rest under a plastic bag, with enough space for air to circulate, for 15 to 30 minutes.

During drying, water must be transported from the interior to the surface, where it will evaporate freely. To achieve efficient drying, the diffusion rate and evaporation rate must be considered.

The clay then progresses to the leather-hard stage, which generally requires 1 to 3 days. At this stage, the clay is dry to the touch, but still contains a significant amount of water, which makes it cold to the touch. It is brittle and may crumble if pressure is applied to it. At this stage, it is important that the piece is completely dry before firing to prevent it from exploding in the kiln.

Finally, we reach the stage where it is completely dry, which usually takes about 7 days under normal conditions. At this stage, the clay is completely dry, has acquired a lighter shade, is not as cold and is dry to the touch. To prevent the pieces from exploding in the kiln, it is essential that they are completely dry before firing.

It is important to note that these time frames are only general guidelines and that the rate at which clay dries may vary depending on the environment. Humidity in the environment is a key factor. In humid climates, the drying process may take longer, while in drier conditions, the clay will dry faster. Ceramicists can control the humidity in the air around the clay by using methods such as using plastic or creating “humidity boxes”.

What happens during the drying process

Drying is a fundamental operation involving the removal of water contained in molded or unmolded ceramic products. The evaporation method is mainly used to carry out this process.

The rate of water diffusion through the capillaries depends on several factors, such as temperature, nature of the material, particle size and shape. It will also depend on the water content in the paste, the shrinkage of the paste and the relationship between the vapor tension of the liquid in the part and relative humidity.

Diffusion is possible as long as there is evaporation on the surface of the part.

The shrinkage process during drying should not be forgotten. During drying, the parts undergo shrinkage in their dimensions, which is directly proportional to the amount of water evaporated. These contractions can occur in three distinct phases:

• Shrinkage due to the elimination of water (shrinkage water).
• Contraction during pore formation (pore water).
• Contraction related to evaporation of pore water.

How to dry clay fast: Controlling room temperature and humidity

It is important to avoid drafts and sudden changes in temperature so that there are no possible cracks or deformations. If you are looking to speed up the process, you can use a fan or a dehumidifier, but you must do so with caution so as not to put the piece at risk, some people use radiators, everything is to see in turn the cost of keeping these electrical equipment on and its consumption, which is now more expensive than ever.

Cloths can be used to absorb moisture.

If we want to dry the clay quickly and in a short time, it is key to control any acceleration to the process so that the piece does not become more fragile and brittle and the dreaded cracks appear.

Be careful if we dry it in the open air, the external part may dry too much and water may remain inside, causing the piece to break during cooking.

* Curiosity: Did you know that in some ancient cultures, clay was dried in the sun as a way of thanking the gods for providing them with this valuable resource? The relationship between mankind and clay is deeper than we imagine!

Industrial drying in ceramics

Sometimes, in the art world, industrial dryers have even been used, and the choice of the appropriate drying technique depends on the type of product and the specific conditions. Some of the drying techniques mentioned include:

a) Infrared drying: This technique uses infrared radiation to heat the ceramic material from the inside, which accelerates the drying process.

b) High frequency drying: This technique uses microwaves to dry the clay quickly, being especially effective in products with fast firing cycles. Note, we do not refer to using the domestic microwave. For this you can make a capsule according to this article.

c) Spray drying: In this technique, the slip is dispersed in a hot environment, which allows rapid evaporation of the water.

d) Hot air drying: This is the most common technique in the ceramic industry, where hot air is used to gradually remove moisture from freshly molded parts.

Drying in the ceramic industry is a critical process that involves the controlled removal of water from ceramic products. A variety of drying techniques are used, each with its own advantages and specific applications, and factors such as temperature and humidity must be considered to achieve efficient drying and avoid damage to the ceramic pieces.

Conclusions on how to dry clay:

Clay is a living material that speaks to us, tells us stories and challenges us at every step. Learning how to dry it properly is only part of the journey. This article has been written with the utmost care and dedication, based on outside research and personal experience. It is always advisable to test before applying any new technique on important parts. I hope it has provided you with a clearer picture of how long it takes for clay to dry and how to do it in the best possible way.

* References:

1. Drying of Ceramic Products Dr. D.A. ESTRADA and Dr. J. ESPINOSA DE LOS MONTEROS (Institute of Ceramics and Glass)
2. The Pottery Wheel
3. The Spruce Crafts
4. Soul Ceramics
5. Ceramic Arts Network
6. Spinning Pots