White film on clear glass

Sounds like devitrification (when glass starts to crystalize).  Glass meant for fusing is formulated to reduce this - though it still happens.  Stained glass generally "devits" more readily.

There are some commercial oversprays (also called devit sprays and overglazes) that may help.

Here's a link to a recent discussion on fixing it after the fact.

http://fusedglass.org/node/523

Make sure you are cleaning your glass well and spending as little time in the 1350° - 1400° F range as possible.

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Paul
FusedGlass.Org
Helios Kiln Glass Studio
PaulTarlow.com

Are you grinding the edges?  That promotes devitrification unless cleaned very very very well.

Unless circumstances dictate otherwise, I normally groze my glass if I didn't cut it accurately.  The heat of the kiln will smooth out any little edge imperfections.  Different of course if the glass pieces are butting in the middle.

Stephen Richard

blogs at: http://www.verrier-glass.blogspot.com/   and  http://www.glasstips.blogspot.com/

This is a persistant problem for many fusers. The cause is usually ginding the edges with too coarse a bit. When you grind, you need to use a fine bit on the last step and even then, use a devit agent. I use clearcoat, but the others are fine.

Also, you mentioned "cheap glass". I assume you are not using a glass from Hobby Lobby. If so, that can be a possible additional culprit.

Barry Kaiser

Web Site    www.kaiserglass.com

Glass Classes:   www.Kaiserglass.com/classes.html

Tutorials      www.kaiserglass.com/tutorials.html

Hi Everyone

thanks for the replies.  No I didn't grind the glass, the film is actually on top and not around the edges.  The glass I used was fusable Spectrum 96, but I meant cheap in price (not sure about quality though).  I guess I should try a shorter time at 1460 and see how that goes.  I also have 3 shelves so maybe trying the clear on a different level, have already tried top and middle shelf to no avail, but maybe the time is the culprit.

Then it looks like inadequate cleaning may be the problem.

Stephen Richard

blogs at: http://www.verrier-glass.blogspot.com/   and  http://www.glasstips.blogspot.com/

Hi...holding 5 to 10 minutes at 1460 - 1475 should not a problem, but if you are holding too long on the ramp just prior to that, as mentioned in the previous threads, through the range where crystals can form, it could lead to a problem. It wouldn't be because it's System 96, and I'm not sure that true devit is even the issue here, and agree that there is probably something on your glass that's the actual culprit. Thoroughly cleaning the surface and edges should prevent this from happening again. Make sure you have enough space/airflow between shelves too (ideally, at least 4-5 inches or more), so you can avoid trapping any "gassing-off", which can sometimes mimic devit, but isn't the same. This rarely affects clear or transparent colored glass, but maintaining a good airflow between shelves is always recommended regardless of what you're fusing. Hope this was helpful.

For my information: If gasing off leaves a residue on the glass and it can't be cleaned off, how is it different from devitrification?  Is there some other way of taking it off before re-firing?  What other things on the glass might imitate the devitrification process?

Stephen Richard

blogs at: http://www.verrier-glass.blogspot.com/   and  http://www.glasstips.blogspot.com/

I am also a novice at fusing glass. But I also wonder if it is do to the glass being "clean". I found out early on both glue type and how clean, or not clean, the glass is can contribute to disappointing firings, like white film. 

What I have found helpful is to make a record of what I used to design a piece. I have a notebook, I log the sizes, type of glass, glue used etc. I record all this BEFORE ITS FIRED. After firing, I add comments as to the firing temps/times and the result, and then try and decide what I could have done differently if I have a poor result, or with a great result what to do to achieve the same result in a future piece.