One of the techniques I learnt in the past year is burnout, where clay is combined with combustible material, usually organic, which burns away when fired.  It is a modern idea, although organic additions are not new.  Adobe and cob are unfired mixtures of clay, sand and straw and have been used as building materials for thousands of years.  The straw tubes promote even drying, preventing cracking.  They do not, however, yield a viable fired ceramic and it took technological advances in the 20th century for burnout to take off.

In the 1990s artist and researcher Rosette Gault developed paper clay, a homogeneous mix of cellulose fibres and clay.  The tiny tubes of cellulose act like the adobe straw, but burn out completely in the kiln, leaving a lighter, less dense clay body.  This is useful for thick walls and large pieces but the cellulose also gives strength to the raw clay, which can be made extremely thin.  The cellulose tubes facilitate wetting as well as drying and the unfired clay is resilient and versatile.  It can even be used as a filler on fired work (see my pig below).  Here is a sculpture (69x48x8cm³) by Barbro Åberg, made with paper clay and perlite.  The small pieces of perlite (another combustible) add visual texture by giving a pockmarked look to the clay surface.

 

Burnout is used industrially to make ceramic foams, which have commercial applications in thermal insulation, electronics and pollution control.  A polyurethane sponge substrate is soaked in geopolymer slurry (clay slip, really), then dried and fired to produce an open-cell ceramic foam (Kovářík et al., 2017).

 

Closest to my heart is the work of Helen Martin who, like Helen Gilmour (see my previous post, Knitting and Ceramics), knits her own pieces, saturates them in slip and fires them.  The emphasis is on saturates – she soaks them for several hours – and this would be an obvious improvement to my own attempt at this process (below).  The burnt out yarn has clearly left its mark on the fired clay.

 

This is what I made.

Knitted pig

Using 100% alpaca yarn I knitted a pig, an experimental trial-and-error piece, knitted in the round.  For knitting nerds (knerds?) here is the Knitted Pig Pattern.  I inflated a balloon inside the pig before sewing on the ears and trotters to help with positioning.

 

Note the long tails of yarn to use as shapers once the slip has been applied.

 

 

 

Next I dipped the inflated pig in porcelain casting slip and suspended it inside a wire mesh wastepaper basket to dry.

 

Note how the long tails of yarn are pegged or tied to supports to keep the extremities in shape (they need adjusting as the slip dries).  The wire mesh is particularly useful for this.  I added more slip to areas where the black yarn showed through to avoid cracking (unsuccessfully).  I also pricked the balloon in the wrinkled part near the knot so that it deflated with the drying (and shrinking) slip.  Once dry, I carefully removed the balloon and cut a slot in the back.

 

Pre-bisque

A suggestion of a curl in the tail.

 

 

 

 

 

Unfortunately, the pig developed cracks where the legs joined the body so I repaired these with paper clay slip and rebisqued.  Paper clay is perfect for this – it doesn’t even need to dry before being refired.  The pig was fired on its back, supported by sand to prevent further cracking.  The yarn has now burnt out, also the grey pigment in the slip.

 

I glazed the inside, added black eyes and fired it.  The paper clay repair to the right front trotter wasn’t strong enough and it collapsed in the kiln (more supporting sand?).

My pig, immortalised in clay.

 

The eminent potter, Chris Keenan, described it as the love child of a piggy bank and a clanger – I think he’s onto something.

 

 

 

 

Future plans?