Ceramics, stoneware, porcelain…oh my!

It can seem like there are many different words used for pottery…and it can get quite confusing! Generally these are pretty interchangeable and usually someone will understand you whether or not you use the right term so don’t stress out too much. However if you are keen to get the lingo spot on and understand what pottery is in a little more detail, then I have a short guide for you below.

Clay…what is it?

The clay you use in class or in the studio is most commonly a commercial mixture of different materials that gives a consistent, malleable clay that you can use in hand building or on the wheel. Clays such as kaolins, fire clays and ball clays are mined and processed before being mixed with fluxes and fillers which give you the type of firing temperature and texture you are after. Like a recipe, this mixture will give you the results promised on the bag…as long as it’s cooked to the correct temperature!

Why cook it at all? Could I cook it at home? Why am I saying “cooking”…it’s firing in pottery!

It’s probably best not to cook it at home! The temperature required for pottery clay to become “mature” (i.e. obtain the correct density and strength for the intended use of the item) is usually in excess of 1000°c (1800°f) so you will need a kiln to reach that heat.

The reason clay needs to be heated and not just air dried is to remove all the water. Ambient temperature will dry the water that is simply mixed into the clay mixture (giving a “bone dry” piece) but some water is bound chemically as hydroxyl. This needs temperatures between 400-700°c (750-1300°f) to be removed, a process which permanently changes the clay.

In fact, potters love firing so much they do it twice! The first firing is to a lower temperature, generally around 1000°c (1800°f). This is known as the bisque (or biscuit) firing. The clay is now much harder, often has changed colour but is still porous at this point. This makes it the ideal stage to apply glaze because the porous clay will easily absorb the watery glaze.

The next firing, known as a glaze firing, will go to a higher temperature. This makes the clay even more dense and glass-like as well as transforming the glaze from a powdery coating to a glossy, dense surface. Glaze is a mixture of finely ground minerals held in suspension in water. Exposure to sufficient heat melts these particles together and fuses them with the pottery beneath. With the right firing, both the glaze and clay become water tight giving a functional and (hopefully!) beautiful piece.

So what is the difference between earthenware, stoneware and porcelain? Are they all pottery?

They are all pottery, they are all ceramics…and yet they are all different…sorry!

Earthenware

This is the lowest firing of the bunch at around 1000-1150°c (1830-2100°f). So low that despite reaching functional maturity, the clay is nowhere near vitrified. This means that water can still pass through it/be absorbed into the piece. However, with a well suited glaze you can still have a lovely functional item, just be sure to handwash and check whether it is microwave/dishwasher safe.

Earthenware is the most ancient formulation of clay. The majority of ancient Chinese, Greek, Roman pots you see in history books are likely to be earthenware. In fact the earliest known pottery was earthenware. It was found in the Anatolian region of Turkey and dated to 9000 years ago!

Some modern potters producing beautiful earthenware include Ben Carter (https://www.carterpottery.com), Ann Van Holy (https://annvanhoey-ceramics.be), Fraces Savage (https://www.francessavage.co.uk) and Gabriel Nichols (https://gabrielnichols.co.uk).

Stoneware

Probably the most common type of clay used, especially in a class setting. This clay is usually fired slightly higher than earthenware (around 1200°c/2200°f) so is more dense and no longer absorbs a significant amount of water (fired to vitrification) resulting in a more durable vessel. This clay can be used in the oven, microwave and cleaned in the dishwasher as long as the glaze allows. Stoneware comes in a huge array of colours (red, grey, white, brown, black..) and is lovely to throw with or use for handbuilding.

There are hundreds of ceramicists that I love who make exceptional work. A few examples include Florian Gadsby (https://www.floriangadsby.com/about), Peter Beard (https://peterbeard.co.uk) and Sue Scobie (http://suescobie.co.nz/about).

Like these ceramicists, I use stoneware to produce my pieces. Sometimes I’ll experiment with a coloured or speckled clay (I have a weakness for novel pottery buys) but I always comeback to my classic white stoneware as it throws so well, is fairly tolerant and shows glazes beautifully.

One thing I haven’t tried yet is porcelain…

Porcelain

Generally this has the highest firing temperature of all three clay types. It is renowned for being tricky to work with as it is not as stretchy as stoneware and can absorb a lot of water so can collapse before you know it! A clay for the more experienced potter and one that can give stunning results. Many love to play with its ability to be pulled extremely thin, giving translucent pieces. Take a look at Antoinette Badenhorst’s work (https://www.porcelainbyantoinette.com/#/).

It is the most expensive of the types of clay, owing to its high kaolin content (one of the clay types I mentioned at the top of the article). This also makes it an extremely dense material when fired to maturity so it is great for both everyday tableware as well as beautiful pieces of art.

Some inspiring ceramicists that work with porcelain include Liz Mazurek (https://lizpotz.com), Hammerly Ceramics and Tamsin Arrowsmith-Brown (https://www.tamsinarrowsmithbrown.com).

I hope that clears (some of) that up!

As I’m sure you have gathered, ceramics is an extremely diverse area of art. There are so many different tools and techniques that it can sometimes get a bit jargon-y. However something that might help you out is knowing that almost every potter I know loves talking about pottery! So if in doubt, ask. You might get more information than you bargained for.

Joanna

Sources

https://www.britannica.com/science/clay-mineral/Chemical-and-physical-properties

https://digitalfire.com/glossary/vitrification#:~:text=The%20term%20vitrified%20refers%20to,durability%20for%20the%20intended%20purpose.

https://www.britannica.com/art/earthenware

https://www.keeeps.co.uk/blogs/potters-block/pottery-for-beginners-the-4-main-types-of-clay