Welcome to the factory tour.

Our first stop is the casting shop in the UK’s largest manufacturer of ceramics, based in Stoke on Trent. Casting is the first step in a long process that clay will undertake on its journey to become the ceramic we all use or see in our day to day lives.  Slip casting is used to mass produce intricate shapes that are more difficult to replicate than using techniques like production throwing or pressure casting.

So let’s get started, casters begin their day early around 5:30am to prepare their work stations ready to begin making.  Each caster will work from two parallel benches. If you imagine a cattle grid the top of a casters bench isn’t too dissimilar. 

Now for the moulds, made from plaster and in all shapes and sizes, which line a casters bench in rows.  They can range in size, from a Rubiks cube to a microwave. Plaster moulds are porous, making them perfect for casting. The moulds absorb moisture from the liquid clay which allows the clay cast to shrink away from the plaster edge, making it easier to remove from the mould. A mould will be used for casting for around 5 weeks twice daily, deteriorating with each use, cast too often and moulds become wet and unusable until dried.  

 Liquid clay known as slip, moves through the factory via a labyrinth of pipes attached to the ceiling.  Hosepipes connected to these allow a caster to pour large quantities into the moulds throughout the day.  Casters work with different types of slip.  The most common is earthenware which produces a more heavy, durable ceramic finish. Another type of slip often used is porcelain which is smoother and less forgiving than other clays. These are differentiated at this stage foremost by colour, earthenware is referred to as pink even though it is grey. Porcelain is bright white.

Slip casting comprises of three steps, fill, tip and empty. 

Filling as mentioned before involves pouring liquid slip into plaster moulds. Timing at this point is imperative and figuring out the casting times needs to be accurate. Most,  if not all casters will do this by eye, judging the thickness of clay gathered at the top of a mould as an indicator of the casting time and clay density.  Leave a mould too long and you’ll end up with a jug more akin to a doorstop, too little and the clay will be too fine and likely to crack in the firing process. 

Next is tipping the moulds which allows excess slip to drain away. This leaves behind the casted shape of your pot. Start by slowly tipping your moulds to drain the liquid clay at an angle, then leave them to stand. This allows the slip in the mould to harden. It’s best not to rush this part of the process, tipping too fast, will not end well. Your cast will probably sink, taking on the shape of a deflated balloon. 

After allowing drying time you’re ready to empty your moulds. Cutting away any scrap clay left behind by the filling process makes it easier to remove the pot from the mould leaving a cleaner finish. It is then time to smooth and sponge any sharp edges you’ve cut away. Finally, removing your pot from its mould and putting the pieces of the mould back together securing them with elastic bands. Within a matter of minutes you can go from having something the same consistency as gravy to an actual jug or tea pot.

These steps might all sound straight forward but let me assure you they are not. Bench Casters are skilled craftsmen and women, who produce large volumes of ceramics of the highest quality,  day-in day-out by hand. Each caster will fill, tip and empty every mould they have twice a day, with counts exceeding 400 pieces. Now that’s a lot of pots! 

Get in touch to discuss your own experiences by emailing Sisu at sisuceramics@gmail.com or follow Sisu for more stories from the factory. Up next, Spongers!