Entrapped Water

[Lynn Perry]

I believe Brock posted about how long it takes to evaporate entrapped water. I have been using 500 degrees/hour to 180 degrees with a 30 minute hold for small 5/8" x 7/8" pieces, but the corner on one piece exploded during the firing yesterday. The smaller piece moved about three inches, while the larger piece went about six inches where it fused to the two others.

For future firings for small thick pieces with multiple submersions in water, I think I am going to raise the temperature to 190 degrees and extend the cycle to full hour. Should have paid more attention to Brock....

[Cheryl]

212. water evaporates at 212 degrees

[Morganica]

Probably a dumb question, but why is the water entrapped?

[nigeljohnson73]

212. water evaporates at 212 degrees

Careful, water boils at 100C (212F) and you probably don't want the movement and bubbling associated with that. Water evaporates at any temperature above 32F, but faster higher

190 is a REALLY hot cup of coffee, so a good temp to let the water out slow enough not to cause a problem, but the original question remains, why is there water in the piece?

[Lynn Perry]

Hi, all. Thanks for the information and suggestions. The water is entrapped within the little nooks and crannies of the ripple and combed glasses which remained after full fusing into 1/4" thick slabs. This glass has been cut with a saw, smoothed with a flat lap, and ground to shape with a regular grinder. After each of these processes which use lots of water, the glass has been submerged in water to keep the edges wet while the pieces are dirty and prevent the grey halo later. I rinse the glass pieces completely with water before the each process, but I don't fully clean them with alcohol until I am ready for fusing, in this case, a fire-polish. There is always a possibility of water within the pieces.

The drying cylce is less the 212 degrees, because I want to evaporate the water without boiling it. I was just surprised this time that such a small piece still had liquid water within the piece. I am almost certain the explosion occurred early in the cycle since all pieces were polished and the three ruined pieces were securely melted together at all of their contact points.

[Mark Wright]

Remember that water boils at lower temperatures as the altitude goes higher. If you ever go to Pikes Peak, CO, elevation 14,114 feet, they will serve you a boiling cup of coffee that you can drink.

[Morganica]

OK, I get it. First, if I didn't have an air compressor on the premises (I don't), I'd hie me to the nearest electronics supply store and buy a case of canned air. Not very expensive, and it does a good job of blowing water out of tiny crevices without worrying about steaming the piece apart. Evaporation can take longer than you think.

Second, 500dph to 180 for 30 minutes may not get enough heat to the water to fully evaporate it--it's possible that you've still got water there and it's actually turning to steam somewhere higher up the ramp. Go up slower/stay there longer.

Third, are you absolutely sure that it's a steam problem and not thermal shock? If there's that much texture on the glass, 500 dph may be a bit fast for an upramp.

[Lynn Perry]

Thanks, Cynthia. All good suggestions.