Testing slips on different clays
Trying out white uni slip (50% ball clay + 50% china clay) applied onto bisque ware instead of onto leather hard greenware. The pattern is painted on with latex, covered with brushed on white slip and then by pealing off the latex resist with the overlaying slip reveals the pattern. This is rather laborious and potentially really quite messy creating quite a lot of dry clay dust. I am not sure whether this will go beyond this test - or indeed if the slip actually fuses with the clay. These go into the kiln in for a second bisque firing.
These are my bisque fired results. It is clear that it matters what clay this slip is applied to. It adheres quite well to the black (PF680) and red clay tiles (PF690). However, it comes off very easily from the white clay tile. Initially I though this could be due to different shrinkage rates during firing as this white clay (PF700G) contains porcelain, which is known to have a high shrinkage rate. However, as it has been pre-fired it will have already shrunk. Hm...
It's a shame that this technique didn't work on white body as it would iron out some potential problems for my large pieces built with this clay. I had hoped that I could avoid applying slip to the the figures pre-firing as the addition of moisture of the slips is likely to put a lot of structural strain to the greenware body. This clay is so difficult to hand-build with and quite unforgiving.
So, either I try a different slip, e.g. with added flux to help its adhesion, or bite the bullet and apply the slip before bisque firing or try to find a different white clay...
Trying out two different white slips on the same clay body (PF690) to see the difference in opacity, whiteness and fit with the clay body.
Left: uni slip = 1/2 ball clay + 1/2 china clay
Right: Katie T's parian casting slip
My initial reaction when applying the slips is that the uni slip is much more opaque than the Parian slip. Maybe I should let some of the water evaporate from the Parian slip before brushing it on.
The Parian slip does not stick very well to the clay body and has flaked off in parts. I will have to see how it appears below a glaze.