Wednesday, 24 August 2016

Kiln Forming Myths 30 – Slump Depth

You can slump only 5cm or so per firing. If so, why don't drop rings fail?

This is really about a comparison of deep slumps and free drops.

Multi-stage Slump
·         The stages of a deep slump give more control of the design
·         The shape of the result is determined by the shape of the mould
·         The wall thickness will be much more consistent
·         For its size the deep slump is lighter than the drop. 
·         The multiple stage deep slump is designed to have the minimum of cold work.

Single Stage Slump
·         If you attempt to do a deep slump all at once you run the risk of ruffle around the upper edge. 
·         There are likely to be a large number of stretch marks on the outside.
·         The design will be distorted to varying degrees along the surface.
·         The wall thickness will vary greatly.
·         You lose the advantages of the multi-stage slump without gaining the advantages of a drop vessel.


Drop Ring Vessels
·         Drop rings require higher temperatures. 
·         The glass thins as it stretches through the ring, so you need to start with a much thicker blank than slumping. 
·         There will be a thick base in relation to the sides.
·         The design will stretch, and if properly designed will be very pleasing.
·         The walls of a drop vessel will vary from thick at the bottom to thin at the top.
·         The collar needs to be cut off the vessel and cold worked to smooth.
·         The process of falling through the ring needs to be monitored to avoid an excessive drop causing distortion or an insufficient drop causing the need for grinding a flat base for the vessel.