How to choose
the right clay
Choosing the right clay body can completely change the way your finished ceramic piece looks, feels, and performs. Some clays are ideal for large sculptural work, others are perfect for functional tableware, and some are chosen mainly for their beautiful surface character under glaze.
In this guide, we’ll go through:
- the main types of clay bodies
- firing temperatures and absorbtion rates
- why some clays are suitable for dinnerware and others are not
- the difference between high grog and smooth clays
At 1240.design, we currently focus mainly on stoneware and porcelain clays, as these are the most versatile and durable options for contemporary ceramics and functional pottery.
Quick Comparison
Clay Type
Firing Temperature
Water Absorbtion
Best For
Main Characteristics
Earthenware
950–1150°C
~3–15%
Decorative ceramics, flower pots, beginners
Porous, lower-fired, bright glaze colors
Why Water Absorption Matters
One of the biggest differences between clay bodies is how much water they absorb after firing. This is closely connected to how vitrified the clay becomes in the kiln.
During firing, clay particles gradually begin to melt and fuse together. The more vitrified the clay body is, the denser and less porous it becomes. Less vitrified clay contains more tiny open pores that can absorb water.
For functional dinnerware — especially mugs, cups, and plates — the ideal water absorption rate is generally below 1.5%. Low absorption makes ceramics denser, more hygienic, and more durable. It also reduces the risk of moisture slowly penetrating the ceramic body over time.
High or low
Grog content
Grog (also known as chamotte) is pre-fired and crushed ceramic material added back into clay bodies in various particle sizes. It appears as small grains or speckles inside the clay. The amount and size of grog dramatically affects how the clay behaves.
Grog can also be added to clay manually to adjust both the working properties and the visual appearance of the clay body.
Using grog in a contrasting color (i.e. colored grog from Flecks + Specks) can create beautiful speckled or textured surfaces after firing. Depending on the size and color of the particles, the effect can range from subtle natural speckling to bold terrazzo-like surfaces.
Choosing the right amount
Grog content & size
Texture & Feel
Advantages
Disadvantages
Best For
High
Over 25%
Size: 0,5-2 mm
Coarse, sandy, textured
Excellent structural strength, reduces cracking and warping, holds shape well even in large forms
Rougher on hands, less suitable for fine detail or very smooth surfaces
Large sculpture, handbuilding, slab work, large planters, outdoor ceramics
Low and medium
Between 0 and 25%
Size up to 0,5 mm
Moderately smooth with slight texture
Good balance between workability and stability, easier to throw than heavily grogged clay
Slightly less stable than high grog clay for very large pieces
Functional pottery, wheel throwing, medium-sized forms, everyday studio use
No grog
Silky, smooth, refined
Excellent for fine detail, smooth trimming, clean glazed surfaces, pleasant for wheel throwing
More prone to warping and cracking, less stable in larger forms, more sensitive during drying
Fine wheel throwing, delicate decorative ceramics, smooth tableware
Note: the larger the piece, the more useful grog becomes. Smooth clays are ideal for fine detail and refined surfaces, while grogged clays provide strength and stability for larger work.
Combining
different clay bodies
Combining different clay bodies can create beautiful visual effects and open up many creative techniques — but it also introduces one of the more technical aspects of ceramics: compatibility.
Many potters assume that if two clays have the same firing temperature, they can safely be combined. Unfortunately, that is not always true. Even if both clay bodies mature at the same cone or temperature, they may still behave very differently during firing and cooling.
Coefficient of Thermal Expansion (CTE)
The coefficient of thermal expansion, often shortened to CTE, describes how much a material expands when heated and contracts when cooled. If two combined clay bodies shrink and expand at significantly different rates, internal stress builds up inside the ceramic piece.
This can lead to cracking, separation at joins and tension strong enough to destroy the piece during cooling. This is why two clays can technically have the same firing temperature, similar appearance, similar color …and still be completely incompatible together.
CTE values are usually expressed as:
×10-6 / °C or 10-7 / K
This simply means how much the material expands per degree (Celcius or Kelvin) of temperature change. The higher the number the more expansion and contraction. The lower the number the less movement during temperature changes.
General guideline
Difference between CTEs
Compatibility risk
Very close
(difference lower than 0.5 or 5 if CTE is expressed in K)
Usually safe
Moderately different
(difference between 0.5 and 1.5 or 5 to 15 if CTE is expressed in K)
May work with testing
Significantly different
(difference higher than 1.5 or 15 if CTE is expressed in K)
High risk of cracking or separation
Note: In practice, the closer the thermal expansion behavior, the better. Many ceramic artists prefer to combine clays from the same manufacturer that are designed to shrink and vitrify in a similar way. You will find the CTE for each of the clays available in our store in the data sheet that can be downloaded from the product page.
Most popular stoneware clays
