What are the possible effects of fast rises to a high temperature for a slump?
Some of the possible effects of fast rises to a relatively high temperature slump are these:
Uneven slumps can occur.
· This largely due to differential heating of thicker/thinner parts.
· It can also emphasise anything off level.
· Any unevenness in the heat across the kiln can also be emphasised by the rapid rise in temperature.
Uneven slumps can be promoted by contrasting colours. Dark and light colours heat at different rates, leading to one area of the glass slumping before another.
A dark/light contrast can lead to stress fractures in fast firings.
In a fast firing the top heats faster than bottom leading to the possibility of splits on the bottom of the piece
The edges of the piece heat faster than centre, increasing the possibility of spikes at the edge.
Fast slumps require higher temperatures to achieve the slump. This means there will be more marking of the bottom surface. It often includes stretch marks especially at the rim.
The Alternative to Fast High Temperature Slumps
Slow and Low
Slow rises in temperature means the slumps can be done at lower temperatures. Lower temperatures usually mean more control and fewer marks from the mould. It does mean that you will need to observe at intervals to get the soak time you need, but this is required for all variations in rates and layups, as well as new moulds.