Bubbles redux

Carla · Post by **Carla** » Fri Sep 19, 2003 12:59 pm

Disclaimer:I know I know, there are a million posts on bubbles. I have read a few thousand of them. I have also tried experimenting to fix my own problem. But was hoping I could get some insights on how to problem solve this.

I am in the middle of fusing 8 doz plates and am having all sorts of bubble problems, using a firing schedule that previously worked. Unfortunately I am working under a tight time line so have limited time to experiment. I thought I had worked this problem out months ago. I need help.

I was getting nice tiny little bubbles, I was very happy. Now I am getting huge misshapened lumpy bubbles, doing the same thing.

The schedule and bullseye glass colors I am using is below. Any help you can offer will be much appreciated.

Basic Info:
Plates are 8" in diameter, 2 full layers, no cuts
the Bullseye Colors being fused for 4 different colored plates are:
1442 to 1808 â€¢ 1808 to 1841 â€¢ 1807 to 1820 â€¢ 1820 to 1834
Kiln: Evenheat coffin kiln, 41" x 25" x 13"

The schedules that used to work was: ie we got nice small round bubbles

400Â° to 1160Â° hold 30 min <this is my "squeeze step" that use to work
400Â° to 1400Â° hold 8 min
9999 to 960Â° hold 30 min

I have also tried:

400Â° to 1160Â° hold 40 min <altered the squeeze time
400Â° to 1400Â° hold 12 min < longer fuse time
9999 to 960Â° hold 30 min

And!

400Â° to 1140Â° hold 40 min <altered temp and squeeze time
400Â° to 1400Â° hold 8 min
9999 to 960Â° hold 30 min

Last nite I tried:

250F to 1140, hold 40 minutes <slowed down ramp time considerably & lowered temp
400 to 1400, hold 5 minutes
9999 to 960, hold 30 minutes

I am seeing no appreciable difference in the bubbles problem, maybe it's getting worse.

The only changes we have made since we last did these plates in the Spring are:
â€¢ the BE colors we use
â€¢ putting on the BE kiln wash with a hake brush instead of a paint brush
â€¢ washing the blanks in a dishwasher b4 putting in kiln

Any help you can offer, will be SO appreciated.

Carla[/url][/u]

charlie · Post by **charlie** » Fri Sep 19, 2003 1:05 pm

i don't use a soak, but a slow climb, to minimize bubbles. in my kiln:

400 to 1100 hold 0
50 to 1250 hold 0
400 to 1480 hold 10
anneal

is the glass not as flat as it usually was? are you fusing it with the rough bumpy side in between the layers, or on top? did you used to use double rolled, and now using single rolled?

Carla · Post by **Carla** » Fri Sep 19, 2003 1:19 pm

Ohh. I like that schedule.

The glass should be the same, just switched colors. Don't know if it is double or single rolled, but the 2 smoothest sides are together.

I was wondering if my kiln has had a mid summer temp switch, got a dirty thermometer, etc. I figure once I get some time, I WILL get a dealy to check the internal temp of this kiln. But in the meantime, I have a gun at my head.

C.

PS: I spent my early life in Arizona and still claim the state as mine. But I don't know where Cave Creek is.

charlie · Post by **charlie** » Fri Sep 19, 2003 1:48 pm

Carla wrote:PS: I spent my early life in Arizona and still claim the state as mine. But I don't know where Cave Creek is.

it depends upon when you were here. it's currently about 15 miles north of phx, but when i moved to phx 25 years go, it was a LOT further. and no, plate tectonics doesn't come into this in any way. phx is currently one of, if not the, largest cities in the US in square miles.

charlie · Post by **charlie** » Fri Sep 19, 2003 1:50 pm

i forgot to ask: are the bubbles between the layers, on the bottom, or on the top? the solution is different depending upon this answer. the slow intermediate schedule i previously gave solves (for me) the bubbles between the layers.

SAReed · Post by **SAReed** » Fri Sep 19, 2003 2:21 pm

I spent many summers camping in Cave Creek....when it was FAR away from Phoenix....took forever to get there. It's beautiful country!

Carla · Post by **Carla** » Fri Sep 19, 2003 4:03 pm

Bubbles are between layers.

What is so frustrating is that I had few bubbles a few months ago. Now that the cosmo's have shifted I full of bubbles and big lumpy ones at that.

Carla

Tony Smith · Post by **Tony Smith** » Fri Sep 19, 2003 4:42 pm

Carla, if you are having "mumps" as I affectionately refer to them, the hold at 1480Â° should take care of it. I found that 20 minutes gives me quite acceptable results. An even longer hold means an even flatter surface, so you will have to decide what is flat enough for you.

Tony

Bob · Post by **Bob** » Fri Sep 19, 2003 4:58 pm

Hi Carla,

Tony calls them "mumps" ... I call them the "dreaded zits". I would suggest two approaches:

1) I would increase the first soak from 1140 to 1250. The glass will be more ductile at 1250 and therefore could squeeze the air out more efficiently. If I remember correctly Bullseye recommends 1250 for what they call the "squeeze".

2) I watch for the first appearance of dreaded zits... means you have to start peaking in the kiln at about 1450 (my kiln full fuses at 1515). Generally by 1480 you will know if they are there. I believe their appearance represents when the glass is "fluid" enough to allow the trapped air to form a spheroid shape rather than the irregular outline. If more heat is applied then the glass becomes more fluid and the air becomes hotter. The combination of these two changes promotes the growth of larger bubbles...... So, if I see the dreaded zits then I reduce the heat and hope that the surface will smooth before the heat works its way into the middle of the glass.

In essence you are attempting to limit the amount of growth of the bubbles.

I bet the sudden appearance of the bubbles is because your original glass was double rolled and this batch is single rolled.

Hope this helps.

Cheers,

Bob

Brock · Post by **Brock** » Fri Sep 19, 2003 5:20 pm

Hmmm . . . I've always felt that if you have trapped air at all, you are pretty well screwed. You can move them, sometimes, you can compress them into a natural corner, or dam, but the longer you heat the glass once the edges are sealed and the buvbbles are there, the worse they're gonna get. Heat it long enough and they'll come through the surface of the top layer. Brock

Cynthia · Post by **Cynthia** » Fri Sep 19, 2003 7:07 pm

I slow the ramp from 1100 through 1250 to a rate of 50 to 100 dph, then ramp up to full fuse temps at 400 to 500 dph. The larger the piece the slower I go. This is a really effective way to squeeze out the trapped air. It's a version of Lynn Chappel's squeeze technique that I adapted for my situation.

From your schedules, it appears that you kept everything the same in this softening but not yet sticking range, so maybe you'll get better results by slowing down through this temp range.

I've heard that some folks have success minimizing the appearance of bubbles by refiring. I haven't experienced that same success, so I try to eliminate them to start with. When you find what works for you...stick with it until it doesn't work anymore.

Good luck

Steve Immerman · Post by **Steve Immerman** » Fri Sep 19, 2003 7:09 pm

Carla,

The single vs double rolled issue is also important. You will get totally different appearing bubbles if one or both of your glass layers is single rolled instead of double rolled. The bubbles are bigger and more oval or teardrop shaped, instead of the nice, unobtrusive, round bubbles you usually get.

I once had 25 full sheets of clear Single Rolled accidentally substiuted for double rolled in an order.

I did a few tests, and the change in bubble appearance was so dramatic, I contacted the distributor and told them I couldn't use the glass. I felt kind of silly, since it was a minor difference, but they understood completely, and paid to ship me a new crate of glass and ship back the single rolled.

So, check and see if your glass number is -30 or -10. It makes a huge difference. Maybe, you can overcome this by changing your firing schedule - but maybe not.

Steve

Carla · Post by **Carla** » Sat Sep 20, 2003 1:44 pm

This single rolled/double rolled has me puzzled. If I understand it correctly, single rolled is very smooth on one side, and doubled rolled is very smooth on both sides.

So, if I am still putting the two smooth sides together, then what difference would it make if my glass is single or double rolled? My bubbles are between the layers.

Am I misunderstanding what these terms mean?

Carla, adjusting her schedule to slower ramp, higher temps and bubbles are smaller!

charlie · Post by **charlie** » Mon Sep 22, 2003 11:10 am

Carla wrote:This single rolled/double rolled has me puzzled. If I understand it correctly, single rolled is very smooth on one side, and doubled rolled is very smooth on both sides.

So, if I am still putting the two smooth sides together, then what difference would it make if my glass is single or double rolled? My bubbles are between the layers.

Am I misunderstanding what these terms mean?

Carla, adjusting her schedule to slower ramp, higher temps and bubbles are smaller!

if you're putting the smooth sides together, not very much. the single rolled has one really bumpy side, and the other doesn't seem to be totally as flat as both sides of double rolled.

WarmGlass.com

Bubbles redux

Bubbles redux

Single/Double rolled= differences & bubbles?

Re: Single/Double rolled= differences & bubbles?