Surprisingly, both porcelain and, to a lesser extent, bone china can be used in the different hand-building processes of coiling, slab building, modelling, press-moulding and combinations thereof, providing certain factors such as joining and careful drying are respected.
As with most clays, the pieces to be joined should be of equal dampness. If one or other piece is too dry, the high shrinkage rate of porcelain will undoubtedly encourage cracking. Use a hacksaw blade to score both surf aces by cross-hatching and join them with a porcelain slip/slurry made from dry body scraps mixed with water. Some makers prefer to use vinegar, as its acid properties will soften the clay, whilst others use just water. Whichever the choice, apply an even pressure between the two pieces to be joined and dry carefully.
Most drying is done slowly, avoiding drafts and extremes of temperature. For smaller pieces, wrap the porcelain in polythene bags. For larger pieces and quantities, make a 'drying tent', which is simply sheets of polythene stapled to a frame construction. This way, the drying of the ware can be monitored.
Slab Building
A particularly individual approach for producing extremely thin porcelain slabs is that of Paula Bastiaansen (Holland).
First of all, she makes a drawing on very thin tracing paper. This helps her to determine how to construct the pattern. If the piece is to be coloured, it is at this point that she introduces the stains. Extremely thin strips of clay, no wider than 1cm at most, are cut and placed meticulously one by one onto the paper pattern. Meanwhile, it is important that the clay retains its moisture. To ensure this she places cling film above and below the strips.
When the 'drawing' is completed, the piece can be laid into a previously made stoneware mould or former. This is a particularly important and decisive moment, for she will have spent several days preparing the work, and has only five minutes to place and construct it in the mould. After drying for a few days, the piece can be put directly into the kiln and fired to 1260°C. During the firing, the porcelain is allowed to distort and convolute.
Bastiaansen's latest pieces are more complicated than the above method, however, being made separately and assembled after firing.