There is a vast range of pottery clay in the market, which has different characteristics and which is ideal for the various forms and techniques in pottery. Selecting the right kind of clay helps in achieving the desired design on the potteries and other items. This guide focuses on what kind of clay to use for pottery, what properties define the clay, what techniques the clay is appropriate for, and what types of pottery projects the particular clay is best suited for.
Clay Types
There are four major categories of pottery clays to consider:There are four major categories of pottery clays to consider:
1. Earthenware: The main component of earthenware is red clay; it is porous and is hardy when fired at temperatures up to 2,100 degrees Fahrenheit. If it is a beginner-level material and the object in question does not retain water, then it is safe to use.
2. Stoneware – This is a pottery that is produced from a sturdier clay that has feldspar content and is fired in a range of temperatures between 2,200 and 2,400 F. Stoneware has minor porosity, has high impact strength, is non-conductive to cracking, and good for oven use.
3. Porcelain – Derived from kaolin and fired at more than 2,400°F, porcelain is harder, impermeable, and heat/end user safe. Ideal for cutlery and fashion products like sculptures.
4. Raku – A form of Japanese low-fired pottery created under high heat in a raku kiln at approximately 1,800 degrees Fahrenheit. Gives a rough surface with crackle effect like the old rustic artifacts.
Key Clay Properties
Beyond clay types, consider these key physical properties:Beyond clay types, consider these key physical properties:
1. Plasticity – The extent to which raw clay can be shaped and molded to desired forms with little resistance. From shortest to longest plasticity: raku fired clay, porcelain, stoneware, earthenware.
2. Drying & Firing Shrinkage – It represents the variation in the size of raw clay through the drying and firing stages. No cracking is observed when the shrinkage is kept to a minimum, but if the shrinkage increases then the cracking risks also increases. From least to most: The subcategories are stoneware, porcelain, earthenware, and raku.
3. Absorption or Porosity – Stating how porous the clay is after the firing process. From least to most absorption: vitreous, semivitreous, non-vitreous, heliothermal, crystalline, milky, porcelain, stoneware, earthenware, raku. Controls water resistance properties.
4. Strength – It prevents an object from having sharp cracks or breaking off easily. From weakest to strongest: Raku, earthenware, stoneware and last but not the least porcelain. Critic for and flexible for forming and shaping the basic structural elements of the finished piece.
5. Thermal Shock Resistance – ability of a material to withstand temperature variations without failure or cracking. Also highest to lowest: hard paste glazes: porcelain, stoneware, earthenware, raku. Essential if food is hot or cold and drinks are intended to be poured into it.
6. Different clay types fire at different temperature ranges or the firing temperature varies according to the clay types used. This should match to your kiln capabilities and make sure that your kiln size effectively meets all the production capacity need by your line of business.
Technique Suitability
The properties above make certain clays more ideal for specific pottery techniques:The properties above make certain clays more ideal for specific pottery techniques:
Wheel Throwing – Stoneware or porcelain is the best material for stretching and shaping on the pottery wheel as the clay doesn’t tear or sag halfway.
Handbuilding – it is necessary to select very plastic earthenware or stoneware since clay at this stage must maintain its shape while being constructed from coils, slabs, or pinched.
Sculpting & Carving – Choose porcelain or if not possible then a very hard stoneware for carving and detail work so that the bisque does not slump or sag after carving.
Raku Firing – Do NOT use stoneware clay or regular clay that cannot handle the high heat of raku firing up to 1,800°F.
More porous is earthenware and raku clay, which lets colored slips, underglazes as well as stains to be absorbed by the clay and in this way used for Decoration.
Firing method – What clay type is suitable for certain firing technique and what firing temperature the creator wishes to achieve whether through electric kiln, gas, pit firing or raku.
Clay Recommendations by Project
Here are some top clay recommendations based on common pottery projects:Here are some top clay recommendations based on common pottery projects:
Everyday Dinnerware – Porcelain also provides consumers with non-porou and microwave safe tableware suited for holding beverages and foods properly. Also highly thermal shock resistant Provides high thermal shock resistance. Consider durable stoneware alternatively.
Ovenware Dishes: Stoneware is an ideal material for cooking, baking, reheating, serving and storing food since it is heat resistant, and has no cracking or breaking when exposed to sudden or extreme change in temperature. This product has a significantly reduced risk of cracking when exposed to changes in temperature.
Garden Pots & Planters – Terracotta is an ideal material for planting pots and planters as it offers porosity that ensures plants are well-drained. Less weight minimizes the chances of the structure getting damaged in case of falling. Experience less of a problem with cracking issues when it is used outdoors.
Home Accessories – Experiment with the shaping of earthenware into decorative objects such as picture frames, vases, ornaments, wind bells. Provides versatility for adding fine features and engravings on the materials. To finish off, add colors with glazes and stains.
Raku Tea Bowls – For raku clay bowls, one should use real raku potter’s clay and fire the works at temps between 1,480 – 1,650°F to get the characteristic crackled glazes and the handmade look of traditional Japanese raku ware.
Sculptures & Busts – for sculpting detail there is very high plasticity simply meaning that porcelain can give us very thin walls and for tall sculptures with possible heavy bases, porcelain has more strength to support them nor deform during construction. Give slick polished finish suitable for human busts.
Where to Buy Clay
Most of the leading brands of pottery clays can be mostly purchased in large arts and crafts stores. Also try to visit the local pottery suppliers and ceramic shops, artist market and online ceramic specialty shops if you are looking for a wider variety of clay brands such as those coming from Europe and Asia. When purchasing clay, one should always go for the accredited brands and resellers so as to be guaranteed on clay quality. Always start by introducing small quantities of any new clay brand to avoid possible adverse outcomes.
Key Takeaways
Selecting clay involves selection of the clay types, technical properties of each type, applicability of each type for the particular techniques envisaged for the project and information specific to the project as per the intended use of the product. This way it is recommended to test clays first whenever possible. To ensure success while working with clay, it is appropriate to match the right clay type to your project!
