Post Annealing Stress fractures - very perplexed

[AnnaSpanna]

I have just sold a light pull on etsy (woohoo) that is made from perfectly normal 104 - prob a bit of effetre trans and then 006 with some 96 frit in it - no more than usual. But all my pulls made around the same time and also quite a few sets of beads, also made around the same time, seem to have developed what I can only describe as stress fractures.

I made these beads towards the end of last year and they were all quite happily annealed. They came out with no cracks or weaknesses in them and then they have sat in their container waiting to be sold. Now several months on they have developed large swathing cracks in them - not like a straight crack that you normally expect to see.  There is nothing loose and they haven't sheared in half like a bead normally would.  I noticed it really last week for the first time but didn't think anything much of it when I sent a set of beads to a friend one appeared to have a small "fracture" in it but it was only 1 of 7 beads that was affected so I put in another free set to compensate.  Another set I've looked at today has a similar crack in 1 in 7 beads. I'm suspecting that it might be because of the ratio on 96 frit to 104 but if that were the case then all of them would go.

Anybody got any ideas? Or am I just going to have to start producing 104 frit for myself for these light pulls and afflicted beads? The most annoying thing is that it isn't all of them.  I haven't dropped the container that they are in - they are in a relatively cold spare room but I have never had this happen before on this scale and so long after annealing.

[Margram]

Are any of them made with clear glass? So that you can check them for proper annealing with polarising filters?
Could be that your kiln is showing the wrong temperature. As elements get older they can produce less heat 

[Andy Davies]

Hi, I guess that there could be a number of reasons for the problem but you might want to take a look at a post I added yesterday.

I've found that I have a temperature discrepancy between the control temperature and the actual bead temperature. It's not unusual in fact everyone has the same issue but I've measured the difference and made allowances for it.

Without knowing more about your particular problem it's imposable for anyone to know what's going on so all you'll get is opinion, I'm sure it'll by good opinion based on experience.

I'm no expert but if you check things out logically there will be a reason for the problem.

Remember that no matter how slowly you anneal a glass mix you cannot overcome the stress created by having an excess mix of dissimilar CoE  glass,  and if like me you are slightly 'under cooking' your beads then you won't be fully annealing them.
That's fact not opinion.

The ultimate test for annealing is time; I'd like my beads to be kicking about in one or two thousand year's time.

     Have a look at this       http://www.frit-happens.co.uk/forum/index.php?topic=43787.0

                                       Kind Regards . . .  Andy