What is a Bubble Squeeze

[Ian]

Hiya JudyK
 I'll give it a try. This it just to try and explain the term Bubble Squeeze and is not a discussion on time and temperatures. That can be another topic.

In the picture we have 2 sheets of glass, one on top of the other. One pink and one green. These are viewed from side on. We want to fuse these 2 pieces together but as you can see there is a slight irregular gap between the sheets where the centre arrow is. Most flat glass is not 100% flat so that when you put one on top of the other you get these minuscule irregularities which contain AIR. So what happens if you put this in the kiln and set your firing schedule to fuse them together as fast as you can?

1 The glass will heat up and it will get to the sticky stage before the top piece {green} has heated enough or had enough time to  drop flat onto the bottom piece

2 The edges will stick together [green arrows] and seal before the top green piece has had a a chance to flatten down onto the pink piece, so now you have an air pocket trapped so all the air has to do is wait for the entire piece of green glass to get soft enough and that is when the air that has expanded due to the heat will push up a BUBBLE because it has no where else to go.
To avoid this a Bubble Squeeze segment is used in the firing schedule

1 The glass is heated to just about the bending stage where the glass starts to move and a tad before it starts to stick together

2 The programmer is set to hold the glass at that temperature to give the air time to escape as the top green piece settles down onto the pink piece [pink arrow area]  pushing the air out from underneath before the edges have sealed

3 When this has been achieved then the programmer carries on with the programme to complete the fusing and when done there should be no bubbles in between the 2 sheets of glass

[Audrey]

You explain things very clearly, Ian. Thanks for all the time you are taking with these explanations.

[Becki]

I don't always use a bubble squeeze...just depends on how my glass is set up.  When I do use a squeeze I ramp 50-75dph from 1050F to 1350F with no holds.  This works for me. It lets the glass slowly squeeze the air out before the edges seal.

[Kev]

So at the end of your bubble squeeze you do not hold and just continue on from there to the peak temp?

[Becki]

Yes. After my squeeze I just go right up to process temp.  My edges are sealed or sealing so there is no reason to hold.

[Kev]

Good to know! I was following that up to 1250 with a 20 min hold and then progressing upward.

Nice to have so many options.

[Becki]

There are different options.  If it works for you then keep doing what you're doing!

[ct4mom]

Love these explanations. They are to the point and easy to understand. And learning one question at a time is better than trying to read everything at once. Great job Ian on these.

[Ian]

Thanks for the comments guys. As long as everything is understandable then mission accomplished.
Ian