|Monthly Tech-Tip |
Which is safest and least likely to crack on drying? The slip cast on thrown. The overall drying shrinkage of the plastic throwing clay is the main issue, likely at least 2% more than the casting clay. A cast mug needs to be stiff enough for handling in order to apply a plastic handle, that will mean that it is well along in shrinkage, not much is left. The plastic handle, conversely, needs to be soft enough to still have flexibility. That means it still has a lot of shrinking to go. While this one has survived, it likely has built-in stresses and therefore is more easily broken off when bumped. The situation is more favourable when a cast handle is applied to a thrown mug. The mug is already stiff enough to handle, perhaps almost leather hard. The handle is removed from the mould as soon as possible because it needs to have a little flex, which means it likely has more water. These factors help to equalize the amount of remaining shrinkage in the two.