WarmGlass.com

I'm pretty new to fusing and slumping and have had a problem with large bubbles. According to the Contemporary Warm Glass book it says the bubbles can be caused by gases given off by the shelf primer. My question is....If I "cure" the primed shelf at 500 degrees for 10 minutes, as per the instructions on the box, will I still need to worry about the kiln wash gases during the fusing?

Thanks!

Ok I'll give this a shot.

I am going to assume that you have mullite shelves instead of fiber shelves. Yes, pre-firing your shelf primer will help with large bubbles that are between the glass and shelf. If the bubble is between layers of glass then you are into a more complicated answer with many many solutions.

Good luck,
Amy

Thanks Amy! Yes, the bubbles are between the shelf and the glass. Can I just clarify that because I'm curing the the wash I won't need to soak the glass at 1100 degrees for 30 min., then slowly firing 100 degrees per hour to 1300 degrees??? (That is what the book suggests doing. I don't want to do both (curing and extra soaking) if I don't have to)

This is my third attempt at this piece and I really want to get it right this time!

Thanks again!

Stacey

Stacy,

I would highly suggest you follow the schedule in the book. The soak and slow rise above 1000 is important because you can trap air between the layers of glass and cause internal bubbles. This soak and slow rise will allow the glass to sag and push the air out the sides before they seal. This is ofcouse if you have top and side elements.

Amy

Thanks, again, Amy! Yes, my kiln has top and side elements.

Is there a kiln god I should be making sacrifices to????

Stacey

Hahaha, that's up to you! Mine is named Myra...

Hope everything turns out right.

Amy

SAReed wrote:Thanks, again, Amy! Yes, my kiln has top and side elements.

Is there a kiln god I should be making sacrifices to????

Stacey

Stacey

Place a straight edge over your kiln shelf. If there is enough of a dip, it can trap hot air and blow bubbles. The solution is a flat shelf. Bullseye Connection sells German shelves that are flat and expensive. Link is above on this BB.

Bert - thanks for the advice. I checked and my shelf is flat. I just bought this shelf and I would have been upset if it weren't.

SAReed wrote:Bert - thanks for the advice. I checked and my shelf is flat. I just bought this shelf and I would have been upset if it weren't.

Many an expensive kiln shelf have dips in them. It doesn't matter much to potters, but it is killer to fusers.

Learn to search the archives of this site. There is a ton of banter about the problems you are experiencing

I was expecting my shelf to have dips because it was a cheap one. I now know what to look for when I buy more.

I have a couple of books for slumping and fusing and after reading through them I'm sure the bubbles are caused from the kiln wash. When I did a search on this forum I didn't see anything for that particular problem. I did learn a lot though.

Those kind of bubbles can also be caused by uneven thicknesses of glass in my experience. If they persist, the only sure fire solution is to fire on fiber paper (1/8" or thinfire). However, my worst spell of bubbles was indeed caused by a dip in the shelf. Did you slide a piece of paper along between the straight edge and shelf? Sometimes a dip that you can't even see by eye can cause trouble.

Lynne

Thank you, everone, for the information! I have the piece in the kiln now, and I sacrificed a Diet Coke to the kiln god, so we'll see what happens


Stacey

SAReed wrote:I'm pretty new to fusing and slumping and have had a problem with large bubbles. According to the Contemporary Warm Glass book it says the bubbles can be caused by gases given off by the shelf primer. My question is....If I "cure" the primed shelf at 500 degrees for 10 minutes, as per the instructions on the box, will I still need to worry about the kiln wash gases during the fusing?

Thanks!

Hi Stacy--

How thick are the pieces you are firing that are getting the big bubbles between the shelf and the glass? 3mm? 6mm? Thicker? Thinner?

Mary Kay

I'm using Spectrum 96, 3mm. Approx. 90% is 2 layers, the rest is 1 layer. The bubbles are forming under the 2 layers.

SAReed wrote:I'm using Spectrum 96, 3mm. Approx. 90% is 2 layers, the rest is 1 layer. The bubbles are forming under the 2 layers.

Hi--

Where the cold glass layup is 2 layers thick, how many millimeters thick is the glass actually?

Mary Kay

Mary Kay - If I'm understanding your question correctly, each layer is 3mm thick, so the 2 layers would be 6mm.

Stacey

For what it's worth - this problem had me tearing out my hair for multiple loads of glass! I pre-dried the kiln washed shelf in the kiln to 1000; I air dried it in the house; I bought a new shelf from B Eye. I live in a damp climate near a river and thought the shelf must be absorbing an incredible amount of moisture. I finally gave in and bought thin fire shelf paper. I have not had a bubble, big or little since. I tried to avoid the additional cost of paper and fusing but in the meantime was throwing good money after bad with holes and bubbles in everything! Hope you figure it out- it is so frustrating!

Riverdance - I fused the piece with an EXTREMELY slow ramp up and 25 min soak and that took care of the bubbles...but I think a bubble tried to form in the center, there's a little distortion there. I going with the shelf paper next.

I slumped the piece yesterday and it slumped perfectly but, I now must figure out the trick to properly applying the Super Spray. It's not smooth or shiny.