Slipcasting & Fettling
Fettling a mug.
Fettle.
Verb. trim or clean the rough edges of (a metal casting or a piece of pottery) before firing
I love ceramics, I didn’t intentionally set out to work with clay, it just happened, I took a path and ceramics was there, so I followed it; that was over 30 years ago.
I use an industrial method of making to make slipcast tableware using a coloured porcelain. I use a standard porcelain clay and mix it in a blunger, a big mixer, adding water to turn it into liquid clay or slip and add ceramic colours and oxides to achieve a variety of hues.
The slip is then poured into porous plaster moulds, allowing the slip to set and form a thickness on the inside of the moulds, partly by capillary action and partly by the addition of sodium silicate to help suspend the particles of clay in the water, producing a fluid slip.
Its’ a wonderful transformative process. The action of pouring a creamy porcelain, almost like ribbons of flowing silk into pristine white plaster moulds is beauty in itself. After 10 minutes of casting the slip is poured out, leaving a cast, a layer a few millimetres thick behind, the surface has a sheen akin to a shell. The word ‘porcelain’ is thought to have been coined by Marco Polo from ‘porcellino’, which refers to the translucency of a shell.
Once the cast dries slightly in the mould it becomes the consistency of chocolate, soft enough to give a little when touched. If left longer it dries and can give a satisfying snap like set chocolate.
In pottery terms, the clay needs to be leather hard so it can be handled without distorting; clay has a memory, so a slight knock to the form, even if you readjust it and push back into shape, the clay will remember the distortion and revert back when fired.
The first stage of casting requires timing and patience. Judging the right thickness of a cast is important. Each batch of clay usually behaves differently even if the same recipe is followed. The quality of casting slip being influenced by the ambient temperature, the amount of agitation and how long the batch has been resting. To be able to reproduce the same each time, understanding of the clay’s thixotropy or thickness is key so that the consistency can be captured and documented and replicated.
The thickness of a piece conveys so much. We all have our favourite mug in the cupboard. For me 3mm is borderline on being too thick. Whereas an almost translucent thin bone china cup is just too much the other way. Striking the balance and reproducing each cast the same is a skill which takes time and patience.
For me, this is so important, I strive for continuity and being rewarded with a satisfying line of sameness is huge!
But, once the right thickness has been achieved, the final fettle has so much influence on what the finished piece looks like. I’d like to give an acceptable radius guideline, but really this isn't measurable, it is on paper, on a technical drawing and it can be specified. But the judgement is in the hands of the fettler. And…I love this job. It’s the final casting of the eye over a piece of work, the sign off.
Like most craft processes it relies on hand eye coordination, but more than that, it relies on haptic skill and tacit knowledge, an accumulation of skills that are developed over time. It’s a balancing act, understanding of the material and knowing how much pressure to use, how much to take away and to know when a piece is finished. David Pye used the phrase workmanship of risk. The point where one small slip up (no pun intended) and the whole piece is ruined.
The process of wielding a fettling knife and a sponge doesn’t sound so technically challenging, but all of those unconscious decisions about how the rim should look are vital in communicating the quality of a piece.
Too flat or too sharp interferes with the ergonomics and really just doesn’t look or feel nice. For a mug, it’s an intimate interaction, you pick it up with your hands, so the body of the mug and the handle also have to feel ‘nice’ or comfortable and familiar and obviously need to be ergonomic but the rim is so important as it’s for drinking.
The majority who handle the vessel, won’t be looking and judging what the rim or handle look like necessarily, but you do when you hold it and drink from it, it’s not the eyes that are busy assessing the details, it’s how it feels, the sensation and comfort the edge and the handle give to the tea drinker. It’s a passive assessment.
It’s one of those everyday objects that all of us have in the cupboard, and we all have our favourites, don’t we? The majority of us have industrially made mugs, where the decisions as to how the rim is finished is down to the automatic sponging of a piece in a rotational conveyor belt or have been predetermined by the automatic mould, again, the decision was made on paper by the designer.
Studio slipcasting isn’t so exact or precise, but it can be, there’s a huge amount of satisfaction in achieving uniformity. Haptic skills are derived from observations, but essentially by doing, practising and being present, then eventually it becomes second nature, it’s a meditative or mindful process that allows you to fall into a rhythm, to drift off and the job just happens.
Like most repetitive processes, whether in a monotonous factory setting or a daily routine it probably takes 10,000 hours of whittling and honing a complex set of actions to evolve into a simple subconscious routine that in the hands of the crafts person is made to look oh so easy, it’s one of the most relaxing and rewarding ways to spend a few contemplative and indulgent hours in the studio.
Sue Pryke
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