Heat and time

Stephen Richard

The cause is usually a combination of heat and time, usually too hot for too long.  You do not give details so speculation is required on my part.  I suspect on piece was darker or heavier than the other.  Steep moulds can also cause these uprisings.  A blog post of some time ago may have some useful information: http://glasstips.blogspot.co.uk/2009/11/uprisings-at-bottom-of-slumped-bowl.html

Stephen Richard

blogs at: http://www.verrier-glass.blogspot.com/ and  http://www.glasstips.blogspot.com/

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