Sunday, 10 February 2013

Slump Point Test


A slump point test is useful when you wish to determine the approximate annealing point of an unknown glass. The methodology follows:

Prepare a strip of the glass 305mm x 25mm. Suspend this strip above the shelf on 25mm pieces of kiln furniture. Leave a 275mm span between the kiln furniture. A piece of kiln furniture also needs to be placed on top of the glass to keep it in place.

Example of an extreme case of testing for slump point

Fire at 200C per hour to ca. 550C, then fire at 50C/hour to about 700C. Observe frequently from 600C. Record the temperature when the middle of span touches the shelf.  This is also the slumping temperature of the glass when fired this way. 

Subtract 40C from the “touch down” temperature for the approximate annealing point temperature.