Flash Cooling

I read online that about 1/10th of slumped bottles will show some cloudiness. I noticed this on a couple of my bottles, although the cloudiness seemed to be confined to the same type of bottles while other types looked clear. In researching this cloudiness (devitrification), I read that some people use a special spray prior to firing to prevent the problem while others use the technique of flash cooling their kilns. I opted to try that technique with my 3rd firing.

The idea is to catch the firing schedule at the point that it starts to cool after hitting it's highest point. Then you carefully lift the lid a few times to let heat escape in order to help the kiln cool as fast as possible to the next degree point in the firing schedule. Unfortunately, I was busy doing other things while my kiln was running and discovered when checking on it that I couldn't tell if the temperature was rising or falling! I know there's a button I can push to check which phase the kiln is at in the firing schedule, but I was afraid to experiment for fear that I would hit the wrong one and mess up the schedule.

I decided to wait a few minutes and re-check the kiln. I could see that the temperature was falling so I lifted the lid a few times to help the cooling process along. I know that I missed the optimum time for this, but when I later removed the bottles from the kiln they did look clearer. I was really happy to see this with 2 clear bottles that I'd slumped since clear ones show added labels or pictures better. Next time I'll watch the kiln better and catch it at the right time!



This one is clear enough to see through. My previous ones had areas of clouding.



I'm going to experiment with the upper temperature/hold time a little in order to get the bottle bottoms a little flatter. I also noticed that the tops aren't closing completely when slumped in a mold as they do when slumped without.



I'm REALLY happy with the lack of cloudiness in these clear bottles.



Now that I have a couple of clear bottles to play with, my next experiment will be glass etching. Can't wait!