The transformation of clay is one of the most intriguing phenomena. It can be worked from fine dust into beautiful rock solid sculptures that last for decades.
It is every newbie’s dream to bring clay through this incredible shape-shifting journey. But turning loose clay into sculptures that people gush over is not straightforward and involves seven different stages.
What are the 7 stages of clay? The 7 stages of clay are the dry stage, slip stage, plastic stage, leather hard stage, bone dry stage, bisqueware stage, and glaze firing stage.
The clay takes up different properties as it advances through the stages. Understanding how it behaves in each step is the defining factor between a pleasant and frustrating experience.
If you are a beginner in pottery, clay modeling, or sculpting, then this article will be of immense help. We’ll take you through the elementary yet fundamental lesson of working with clay, which is the seven stages it goes through.
1. Dry/Raw Stage
This is the first stage of clay in its most natural state as it occurred from volcanic activities. It usually resembles powder due to its fine-sized particles but can also be lumpy.
Clay in this stage is dehydrated and has little weight, which has its perks. First, it is easier to store and transport because of its weight and loose form.
Secondly, clay in the first stage doesn’t grow mold, stink, or go bad because it is in its natural dry state.
Most importantly, you have a chance to alter some of its properties if you want to. You can change the texture by mixing in some grog or adding pigments to yield a different color.
You can buy clay in the first stage from the store. There are usually various types, including earthenware, kaolin, ball clay, red clay, and porcelain.
Your choice should be based on what you want to make and the type of kiln you have. This is because the various types of clay fire at specific temperature ranges.
Some people prefer to dig up their own clay as opposed to buying it. If you don’t mind getting dirty, you can grab a shovel and extract this clay from the ground.
The best places to find clay would be a construction site, gulleys, near creeks, and where rivers and streams cut though deposits. Unlike store-bought clay, this kind of clay is chock full of minerals and impurities. It must be filtered before use.
You may also acquire dry stage clay by recycling old unwanted or broken pieces of unfired clay items. All you have to do is use a hammer to crush and grind it back into fine particles.
Whichever method you choose, dry clay is the foundation clay.
2. Slip Stage
The second stage of clay is the slip stage. As the name suggests, this is a slippery, super moist stage of the clay.
To make slip, you add some water to dry clay to turn it muddy. It is at this stage that the clay’s water content is at its peak.
It is the potter’s decision on how runny or pasty the slip will be, depending on what they want to use it for.
You might be wondering what you can do with clay this wet. Well, slip has a lot of significance.
Slip acts as an adhesive that glues together two parts of hardened clay. If you want to attach, say, an arm to a body or a handle to a vessel, you’ll need slip.
To use slip as glue, you must first rough up the surfaces you will stick together. You can use a sharp object to scour them by etching some criss-cross lines.
Next is to apply the slip onto the surface and affix one part to the other. Ensure it is not runny but also not too thick—something like batter or beaten sour cream.
Also, for best results, opt to use slip made from the same clay as the item you are working on. You’ll save yourself trouble while firing since the temperature needs will be the same.
Slip has decorative purposes as well. Usually, powder colorants are mixed into it and then brushed onto pottery to lend it some color. You can make decorative trails as well.
Another use for slip is pouring into molds when performing the slip casting process. You need a runny clay consistency to do this, so this slip should be much thinner than that for decorative or adhesive use.
Whenever working with clay, it is always a good idea to prepare some slip beforehand. Set it aside because you’ll need it from time to time.
And although the slip dries up after some time due to moisture loss, you can reactivate it by adding water. A few drops of vinegar are also suitable for old slip to keep mold and foul smells at bay.
3. Plastic Stage
The third stage is the plastic stage, also known as the wet stage or the workable stage. This is an enjoyable and satisfying stage because you can make the clay do what you want.
At this stage, clay is wet but firm. It holds shape and is malleable too. You can manipulate it into an infinite number of forms using any technique.
Plastic stage clay can be worked into objects by throwing on the wheel, hand building, rolling into slabs, coiling, cutting out shapes, indenting impressions, etc.
As time goes by, the clay starts to harden due to moisture loss. Molding it further becomes harder without it cracking. However, you can still make trims, join parts, and fix decorations.
You do not have to work on clay from the dry stage. Many brands sell their clay in the plastic stage, and it comes in plastic wraps ready to use.
However, if you start with dry clay, you must be careful to strike the perfect balance between the optimum amount of water and clay.
If you put too much water, it will collapse, and if too little, the molding will be a horrendous task, yielding many cracks. Both these situations can be remedied.
For excess water, you only require some patience. It will harden a little more each time, so you must keep checking.
If clay won’t be manipulated without breaking, it is a sign that it is too dry. You can add little amounts of water, then knead and wedge.
4. Leather Hard Stage
The leather hard stage of clay got its name from how the clay feels to touch. It has a similar feeling to soft leather.
This clay is much firmer than the previous stage. And at this phase, it should be a defined image of the final product.
Molding it at this point would be a terrible idea. Still, it is not yet completely dry and has the right amount of moisture for modifications like trims, fine details, and bonding parts.
Pots thrown on the wheel are overturned to have the foot or base carved at this stage. Also, slab joining is done at the leather hard stage.
If you find your handles or other attachments falling off, it is a sign that the clay is too wet. But this shouldn’t be a problem. You’ll just wait a while longer before trying again.
Clay dries a little with every passing minute. It is easy to miss this stage if you’re not careful. Sometimes it gets too stiff to make any alterations.
Unfortunately, you cannot remedy the situation to make any changes. If anything, it can only be sanded down or smoothed with a damp sponge.
Therefore, if you are working on several pieces or slowly over a long period, you can prevent the clay from drying by wrapping the piece in plastic wrap. It will seal in the wetness, and you can continue later or even another day.
5. Bone Dry Stage
Next is the bone dry stage. Clay in this stage has completely dried out and is ready for firing.
From the leather hard stage, the clay takes a couple of days or weeks, depending on your surroundings, to fully dry. If your region experiences low temperatures and high humidity, you’ll have to sit them even longer.
One sign of completely dried-out clay is the color. It will appear much lighter than what it was while wet.
But clay may appear dry on the outside and still be moist at the core. Firing such clay will automatically end up in cracked pieces and kiln explosions.
To ensure that it is indeed dry to the bone, seasoned clay artists carry out what is called candling. In candling, the pieces are placed in a kiln set at extremely low heat to drive away any trapped moisture.
Although the clay is solid hard, it is also delicate, so any careless handling may lead to breakage. Therefore, the final touches before firing must be done gently and nothing major; just smoothing out edges with sandpaper or a wet sponge.
If the item unfortunately breaks or perhaps doesn’t turn out as you hoped, it is irreparable. The good news is, nothing goes to waste.
Clay in the bone dry stage can be recycled to stage one clay. You only need a hammer to crush it into tiny particles, then soak it in water to make slip.
6. Bisqueware Stage
The sixth clay stage is the bisqueware stage, where the clay goes into the kiln for the initial firing. The firing occurs at cone 04-08 or around 1,900°F.
Bisque firing eliminates any chemical bonds present either by water or impurities, making the clay harden further. At this stage, it is no longer clay but ceramic.
This firing, however, doesn’t alter its porosity. The clay remains receptive to fluid; therefore, it absorbs glazes really well.
The glaze is part water and part clay plus silica and colorant, so it blends in nicely. Applying glaze transforms your piece, giving it vibrance and a smooth glassy finish.
You can apply an underglaze first, followed by a clear glaze. Underglazes are available in an unlimited color range, giving you the freedom to play with patterns and prints.
There are three ways of applying glazes; brushing on, spraying, or dipping. Whatever method you choose, ensure you reach complete coverage.
Three coats of glaze are recommended so you don’t miss a spot and also get the ideal thickness. Proper drying in between coats cannot be overemphasized.
Other optional applications at this stage are embellishments like relief decorations and motifs and an overglaze, which is a clear coat.
Again, you don’t want to go overboard with glaze. Laying it on too heavy will cause the glaze to run down the sides. The results are hardened drip marks. Also, it is tough to retrieve pieces with glaze dried on the kiln.
7. Glaze Firing Stage
The glaze firing stage brings us to the last stretch of the clay process. It is a super exciting stage because you get to marvel at the result of your hard work.
In this stage, the glazed pieces from the bisqueware stage go into the kiln for firing a second time. In the kiln, the glaze melts and fuses with the clay in a process called vitrification.
The temperature settings and time depend on the type of clay you used. There are low (cone 04-06), mid (cone 5-6), and high (cone 8-10) firing clays. Earthenware, stoneware, and porcelain are good examples of each kind, respectively.
You must also ensure that the glaze applied corresponds with the clay’s firing temperature. If it is too high or too low, the glaze will just keep melting and fail to vitrify properly.
After 12 hours or so, depending on the type of kiln, the ceramic ware is now ready for use. The vitrification process makes it non-porous. You can finally take it out and marvel at your creation.
Those are the seven stages of clay. Mastering them is of utmost importance for any beginner because every technique and process revolves around them.
You’ll be learning what to do with the clay in each phase, so it is essential to distinguish them. Having a deep understanding of the stages also helps you set the correct timelines and know what to expect.
Unfortunately, there’s no alert to indicate that the clay has switched from one stage to another.
The transition from one stage to another is primarily dependent on moisture loss. That’s an aspect you cannot see or measure. You’ll have to pay close attention to what the clay is saying by how it behaves.
Hopefully, this guide will sail you through smoothly as you embark on your pottery-making journey. Let’s finish with a quick recap of the 7 stages of clay.
- No water content
- Dry powdery
- The base for clay building
- Highest water content
- Slurry or paste consistency
- Used as glue, as a decorative layer, and in slip casting
- Wet but stable like dough
- Most pliable and forms any shape
- Good for all techniques
- Slightly wet but physically hard
- Can be trimmed, takes details, and secures joined parts
5. Bone Dry
- Dry and firm form
- Inflexible, doesn’t take alterations
- Can be sanded or wiped with a wet sponge to smooth it
- Precedes firing stages
- Can be reverted to dry and slip stage
- First firing stage
- Drives out any chemical bonds
- Clay hardened further
- Good for glaze application
- Porous and seeps in glaze till it dries
- The final stage, last firing
- Hardest and only nonporous stage through vitrification
- Not necessary for terracotta
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