Diagnosis of Slump Breaks

pot melt broken during slumping

The diagnosis of breaks in slumps is a little more difficult than in full fuses. In full fuses sharp edges to the break indicate the fracture occurred on the way down in temperature and rounded edges indicate the break happened on the way up.  The rationale is that an early break will have the edges rounded by the heating during the way to top temperature, while the break at anneal or lower temperatures will have sharp edges as they won't be subject to high enough temperatures to round them.

The temperatures in slumping are not high enough to round the edges no matter when the break occurred.  If the break occurred on the way up, it will remain sharp, just as it would if it broke on the way down.  There needs to be another way to diagnose when it broke.

The key is to try to fit the pieces back together. 

If the break occurred on the way up, the pieces will separate to some degree – depending on the force of the break.  After the break, the glass will slump into the mould according to their separate places.  When cooled and you attempt to put them together they will not fit perfectly.  This may be difficult to determine if the separation due to the break was small, or the mould shallow and regular.

If the break occurred on the way down, the whole piece will have slumped as one whole piece.  So when the broken pieces fit together, it indicates the slump broke apart during the cooling.