What caused this problem then?

[helbels]

Earlier today I made a twistie of Effetre Dk turquoise, Effetre Sky Blue, CIM Mermaid (or perhaps CIM Rainforest) and Effetre Periwinkle.

I put it over a base of CIM Chalcedony and encased with Reichenbach clear.

Popped beads into the kiln... went back 5 minutes later and noticed that each one had cracked right down the mandrel line despite having been in the kiln only for about 5 mins max.

Beads weren't big, and went into the kiln nice and glowing, so they definitely didn't get too cool.  The instant cracking makes me think it was a major incompatibility issue somewhere along the line.

Any ideas what the cause was?

[Veebee]

I've heard that the CiM transparents hate being encased, maybe some of the opals are just as fussy? What a shame though 

[turnedlight]

I have had that with Chalcedony, I tend not to encase it.

[helbels]

Ah ok, thanks. Good to know that Chalcedony is a fussy bugger - I'll avoid encasing it from now on then    Pity, as they were a nice colour - but at least I realised before I'd made the full set.

[jobead]

I always seem to get cracks if I use CiM with any other glass, I have been told in the past that the annealing temperatures can vary within their range which might explain why they aren't very compatible?