Why Bubbles in Spectrum 96 batch

[David Gappa]

I have a Glassblowing studio and have been having a LOT of problems with bubbles in our glass. We are using the Spectrum 96 cullet. We charge at 2225 deg., throw in 50 lbs and wait 30 min., let cook at 2225 for 2.5 hrs and sqeeze down to 2000 deg over 8 hrs. The next day we rake the bubbles on the surface. The first two vessels we blow never have bubbles. Then we start hitting pockets of bubbles the rest of the day. They are approximately 1/16" to 1/8" dia. By the second day all the bubbles are gone... but I can't wait two days to cook glass and meet my production needs.

Please Help

[Brian Gingras]

when in doubt, use the search feature...lots of discussion on this on the board.

http://talk.craftweb.com/showthread.php?s=&threadid=5876&highlight=charging+spectrum

[Scott Dunahee]

I think you're going too hot. I charge 25# of cold nuggets at a time at my working temp, 2050-2100 and raise to 2150 for 3 hours after it's full and evened out in temp. I drop to my idle temp after that - 1875. I work at 2050 to 2100 and the first day after a charge I MAY have small seed bubbles for about a half hour until the glass absorbs them. Once the pot is up to working temp throughout, it's pretty clean glass.

It's not batch and you don't need to go to batch melting temps.

My issue is cords in the bottom half of the pot. If I potato the bejeezus out of it, I have pretty good glass all the way down, but I usually have to potato twice while doing the melt. If I forget or am not determined enough with the potato, I show cords much sooner than I think I should.

Your mileage may vary.

BSD

[Scott Young]

Originally posted by David Gappa
I have a Glassblowing studio and have been having a LOT of problems with bubbles in our glass. We are using the Spectrum 96 cullet. We charge at 2225 deg., throw in 50 lbs and wait 30 min., let cook at 2225 for 2.5 hrs and sqeeze down to 2000 deg over 8 hrs. The next day we rake the bubbles on the surface. The first two vessels we blow never have bubbles. Then we start hitting pockets of bubbles the rest of the day. They are approximately 1/16" to 1/8" dia. By the second day all the bubbles are gone... but I can't wait two days to cook glass and meet my production needs.

Please Help

I really think you need me to recover from this damn throat/tongue Cancer surgery & chemo/radiation. Then we can get our heads around it and test a few other parameters. Last treatment is Monday the 3rd and I should be able to start putting in time towards the end of March. I do think our cycles are way too hot for the nuggets. I think we should squeeze lower as well. Anyway, when I regain speach again, we can talk...

[Hugh Jenkins]

I would agree that your are going way too hot. Glass workers I respect are going to 2160 and then cooling to working temp and getting good glass.

[Scott Dunahee]

whoa, Scott. My heart goes out to you. My wife went through chemo and radiation 2 years ago and that's nothing I'd wish on an enemy.

You sound in good spirits though, so keep it up!

BSD

[Pete VanderLaan]

too hot. 2160-75F.

[Jane Greer]

For what its worth,
I charge at 2250 with 96 throw in 50lbs wait an hour before adding more, soak for 3 hours, reduce to 1950 for 45 min. then working temp (2100). I have beautiful glass the next day with no seeds.

Jane

[Brian Gingras]

Jane,

Almost sounds like your temps are off a bit on the high side.

[Jane Greer]

Brian,
Maybe, but it works. If I lower the working temp, its too stiff and if I lower the charge temp then I would end up with bubbles longer.At this schedule, no bubbles and no raking needed and wonderful glass the next day.

Jane

[Brian Gingras]

Jane,

my point was more that your(everyone's) temperatures are relative to their own furnace...I built one in NY that read 100 lower on anything over 1900 it seemed...we had to slide the T/C in just an extra 1/2" and it read totally differently.

[Jane Greer]

You're right Brian, I think a lot of time its just a matter of dialing in what works in each ones furnace.
One question I would have for Scott is: is this the first time you have charged the nuggets or is this a problem that has just started in the last few charges?

Jane

[David Gappa]

First of all, I would like to personally thank everyone for taking time out to reply to my particular problem. It is great to see artisians... especially glassblowers, working together toward the common good of glass!!!

Here is our update...
Last night we charged again and unfortunately we had a different kind of bubble problem. We charged at 2100 deg, 50 lb at a time and waited approx 45 min. b/w each throw. We held at 2150 for three hours and dropped the temp to 1875 over an 8 hr time frame. We then held at 2000 for working temp. This time we had millions of tiny micro-bubbles all day long instead of a lot of larger bubbles.

Question... how critical is the "sqeeze"... and is 8 hrs too long? The manufacturer of Spectrum 96 said this would work great and would allow the bubbles to slowly rise to the surface, but it obviously did not work. Do you think we need to bump our charging temp up more or longer? How critical is it to rinse the cullet before throws?

FYI... We have a 350 lb freestanding gas fired crucible with HUB recuperator. Top fired with exhaust flue at the bottom. My bubble problem has been going on for approx. a year now.

Thanks for you help and suggestions everyone.

p.s. Scott, we saved a spot at the bench for you. Hurry up and beat the crap out of that Cancer!!!

[Jordan Kube]

Go back to what you were doing before. Don't rake. Throw half a cup of water onto the glass when you get into the shop in the morning. That will kill the big bubbles. That melt you tried isn't going to work. Half cup of water.

[Scott Dunahee]

I think the melt he tried will work fine, Jordan. He just needs to let his pot reach furnace temp before loading more. I don't think 45 minutes is enough time between loads. What Scott is describing is exactly what happens when I try to load too fast on top of the last charge.

If you run it up to 2100 overnight, the small bubbles will be gone by morning.

BSD

[Brian Gingras]

really sounds like you are putting cold glass on top of cold, or very seedy glass now. 45 minutes? did you check to make sure the first 50lb had melted completely?

[Pete VanderLaan]

Firstly, do your nuggets have bubbles in them? Early spectrum nuggets had lots and lots. Those did not go gently into the good night.

The squeeze is NOT a process in which bubbles rise out of the melt. The "squeeze" as the slang goes is a change in the antimony in the glass from mono to pentavalent. The bubbles are literally re-absorbed into the melt. If there are too many bubbles, they can't be reabsorbed since all of the positions on the outer electron ring will be filled up.

How new is your crucible? I thought it was pretty new. If you didn't change it, that could be the problem.

Are the nuggets dusty? If so, wash them.

I would still stick with 2160-75F . Squeeze at 1975F. Squeeze until the bubbles are gone.

I preferred a squeeze bottle of water to just chucking a cup of it in there but both would work.

Let the charges go completely flat and allow the furnace to regain temperature before charging again.

[Scott Novota]

I know that I am the new guy. I know I don't know anything about this. But I will tell you what I do know and it can't yeild anything worse than what you are getting.


I dump spectrum in at 2150. Leave it for 10 hours at 2150 and have little to no micro bubbles. If you leave it at 2150 for 15 hours it will be clear as water.


Just my experience as limited as it may be. I don't move temp. I don't sweeze, I just let it sit there and do it's thing at 2150. Easy and nice glass.

I have gone though about 1k at this point and no matter what I have done I have never had it look better than just letting it melt at 2150 and never moving it. Granted that is 50 pounds at a time and not a huge vat of glass.



Scott.
.

[Pete VanderLaan]

and of course I left out the possibility that your crown is making a contribution to your melts each time.

[Doug Sheridan]

you might try pre-heating the cullet before charging, we do this and never change the temp above working temp and have clear glass. But, we just charge one or two bags each time. If you need bigger charges, I'd try pre-heating in the annealer.