Newbie – Glass Crumbling

[vmhogan]

I’ve been working with my kiln for less than a year but had some nice results.  Still trying to learn to read/correct problems.  The latest result really has me stumped.  When I opened the kiln everything looked fine but when I went to pick it up the glass crumbled and seems to have pretty much shattered throughout.  Parts are even stuck to the kiln shelf (only 2nd piece on this application of kiln wash.)  The glass was 2 layers of Spectrum 36 and was a 8″ diameter circle.  I had just used pretty much the same schedule on a piece with great results (similar size, same # of layers & glass type.)  Here is the schedule I used:

R300  T900  S15

R500  T1100 S0

R100  T1250  S30

RAFAP  T1400  S15

RAFAP  T950  S45

R100  T800  S0

R200  T700  S0

R400  T100  S0

Any ideas what could have caused this so I don’t do it again? 

Virginia

[Stephen Richard]

The is the classic effect when the glass sticks to the shelf.  Normally, each time you go above 7;20C or so you need to renew the kiln wash.  Some do it over the old if undamaged layer, most get rid of the previous  layer and add new to the clean shelf.

I haven’t seen your shelf or the application of kiln wash to it, so I am guessing.  I think you application may be too thin.  For me I need to apply kiln wash – mixed 1:5 by volume – in several directions while the previous is still wet. (I mention this as one person has interpreted instructions to be like painting wood – letting each coat dry before the application of the next.  This is not intended)  I apply one coat N-S, another E-W, another NE-SW and a final SE-NW.  As I use a pink tinted kiln wash, I can see if the shelf is completely covered.  If not I do the same process again.

At any rate, the glass has apparently stuck to the shelf, so you need to review how you apply the separator.

Stephen Richard

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

[vmhogan]

Thanks Stephen for the response.  I thought I had good coverage on the shelf and your directions are what I do.  I’m using a newer wash so maybe I need to make some changes with this wash.  When I did the first piece on this wash application I had a really hard time getting the wash off the back of the piece.  (I ended up soaking in vinegar and it worked like a charm!)  So maybe more came off the shelf that I expected so…  I often thought I wish I could afford fiber paper for each firing but the lottery hasn’t come through.  I’ll redo the shelf and on to the next project!

I’ve learned a lot this week – which means I’m learning from mistakes. 

Virginia

[Stephen Richard]

Any time you have kiln wash sticking to the bottom of a piece is an indication that you have fired once too often on that application of kiln wash.  It certainly says that you now need to clean the shelf and put a new application of kiln wash on it. (Actually, that you should have done it before this firing.) Experience will show you when you need to redo the kiln wash.

My experience shows me that i need to renew the kiln wash every time I go to tack fuse or higher.

 

Stephen Richard

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

[Author]

Posts