Kiln weirdness

While I was away at my last class, I did a slump firing of a bowl and plate into their final shapes.  When I got back and opened the kiln, I had a rather interesting surprise.  The two pieces pulled away from the edges of the mold to create sort of a ruffled edge to the pieces.  Very strange.  If you want to get a better look at the 2 photos, just click on the thumbnails and a larger image will open.

I'm not sure what has caused this problem, but I think that it looks good in the square plate and not so good in the heart bowl.  I'd love for you to leave comments on the pieces to let me know whether you like the effects or not.  Depending on the responses I get, I might give refiring the heart bowl a try so that I can get a better edge on it.

As I was washing the mold release off of the two pieces, an idea hit me that it might have been caused by the fact that I had not cleaned off the mold release from the molds in between firings.  After I had a firing disaster from not enough kiln wash on the shelf a while back (see this post for details) I thought that more release agent between the glass and the mold would be a good thing and haven't been cleaning off the shelf or the molds in between firings.

That buildup of kiln wash/mold release might have caused the glass to be less bendable around the edges where the release had stuck to the glass as it slumped and then cooled.  Since there isn't any release on the center of the glass pieces and there is some around the edges, it seems kind of logical.  But there I go, thinking again.  It usually gets me into trouble...  I think I'll go ask in the LinkedIn Glass Artists forum...  If there are any glass artists reading this post that have some ideas on the problem, please do leave me a comment!

Next phase...

Well, I didn't get the kiln shelf cleaned off and re-coated with kiln wash on Thursday, as planned.  It's turned out to be more stubborn than I anticipated, even with the four layers of kiln wash that I had laid down.  It needs to be cleaned off with a file and the kiln shelf sanded smooth again in those two spots before I can use it again.  I knew that it would be somewhat of a problem to clean off - that's the whole point of kiln wash in the first place - I just didn't have the first-hand experience with it yet.

So, I'm cheating a bit instead.  When I bought the kiln, I also got about a half dozen kiln shelves in different shapes and sizes.  My thought was that as I started to make a larger number of pieces, I could fire more of them at once by stacking the shelves.  Since each blank is relatively thin - around a quarter to a third of an inch high - I can stack quite a few pieces in the kiln, depending on the sizes of the blanks I'm firing.  When I move on to the slumping, I can't stack as much, since the pieces have much more depth.

I've picked out one of the shelves that will allow me enough room to fire both bowls and I'm coating that shelf with kiln wash now.  I have another layer to go before I can put the bowls in there and get the kiln going.  In my next post, I'll show a picture of the kiln with the bowls on their respective molds, just before I turn it on and heat things up.

By the way, in my last post I didn't show one of the blanks because I thought it would look too weird.  I realized that someone may benefit from seeing and hearing about this, so I thought I would post it anyway.  What you're seeing in this blank is air pockets created during the fusing process.

As the glass gets heated, sometimes when you use thick pieces of glass or many smaller layers between the bottom layer and the clear glass top layer, air pockets can form in the final fused glass sheet.  In this particular blank, I used very thick, laser-cut, dichroic glass geckos and some thinner green leaves over a bed of different shades of brown powdered frit.  As you can see, air pockets formed around the geckos.

I'm not all that worried about it, though.  In the next firing, I'll simply hold the temperature twice as long as I normally would at the last stop before I get to the highest temperature for the slumping process.  That will give the glass time to smooth out before it starts to form into its bowl shape.  When you see the finished piece, you'll see that it has smoothed out and formed perfectly into its shape.  This happened to me once before, when I used some thicker pieces of millifiore rod that caused a large bubble in a bowl blank.  I did the same fix last time and all was well.  I'm sure it will be this time too.

New glass pieces - the good, the bad, and the dead

The new pieces that turned out wellNow that my kiln was back in place and I could start to fuse glass again, I put my first load into the kiln on Sunday afternoon.  When I opened the kiln on Monday afternoon, I had a serious shock - two of the pieces didn't make it through the fusing process!

Molten glass sticks to just about anything, so a release agent is necessary to keep the molten glass from sticking to the kiln shelf as it goes through the fusing process.  There are two ways of protecting the shelf from the glass sticking to it, shelf paper and kiln The broken triangle bowl blankwash.  Kiln wash is a powder mixed with water that is painted onto the kiln shelf, building up several layers to create a barrier.  Shelf paper is a barrier that comes in rolls in varying thickness, from truly paper thin, all the way up to shelf blankets of about 1/2" thickness that can be used to form glass in different ways.  Both accomplish the same thing, but rolls of shelf paper are pretty expensive compared to the cost of kiln wash.  Now that I was working in bulk - seven fused pieces were in this batch - I thought it was time to convert from shelf paper to kiln wash.

So this firing was the first time I was using kiln wash instead of shelf paper to protect the kiln shelf from the glass.  I had put down 4 layers - the package directions only call for 3, but I didn't want to take any chances - layering the washes horizontally, vertically, and in each diagonal direction on my kiln shelf.  Despite the extra layer, there were two spots - one on each of two separate pieces - where the glass had stuck to the shelf and caused friction as the glass heated and cooled and those spots were where the glass had fractured.

Heart shaped bowl blankLive and learn, I suppose... but it was very disappointing after having added the extra layer of kiln wash to be on the safe side, to say the least.  At any rate, I've put an extra layer of kiln wash on the molds that I'll be using to turn the remaining two blanks into their bowl shapes.  Hopefully, that will work.  I've put three layers on the other molds that I've used in my past fusing efforts, but now I'm feeling a little paranoid.

For those of you who aren't already familiar with glass fusing, it's a two step process if you are making a decorative glass plate or bowl.  First you cut and layer glass to form a blank in the shape of the piece that you're creating.  I used a combination of a piece of decorative art glass for the bottom layer, then added fusable glass paint, glass frit (ground glass that comes in varying sized material from a powder to a coarse chunk), stringers (glass rod pulled into a very thin string 1/16" or less in diameter), and laser cut pieces of dichroic glass (glass with a layer of misted minerals applied in a process that causes beautiful effects where the light changes the color of the glass when viewed from different directions), and a clear glass layer on top to add depth and dimension.

Once the sandwhich is fused together to form the blank in the specified shape and size to fit a mold, it goes through a separate firing at a lower temperature where the glass melts just enough to form itself into to the bowl or plate The broken square bowl blankshape.  This is referred to as slumping.  So, once the layers of kiln wash are dry on the molds - the process takes time as the kiln wash needs to dry between each coat - I'll be putting my two bowls back into the kiln for the slumping process, which will probably be happening overnight tonight.

These images show both the sucessful efforts as well as the two fractured blanks that didn't make it.  To make it even more disappointing, those were my first two efforts with the fusable glass paint, as well as my first efforts for those particular shapes.  But at least these pieces do give me a feeling for how the glass paint looks after firing.

Closeup of one of the pendants from the photo aboveThe smaller pieces will be pendants, so they won't be going back into the kiln again - they're done.  All they need is a little sanding to take off some rough edges from the firing process and getting a bail glued on.  (The bail is the jewelry finding that allows the pendant to hang from a necklace.)  I just tucked the bails in place under the piece for the photos, but after looking at them, I think that the ones I used for the photos don't look substantial enough for these particular pendants, so I need to go through my stash looking for some more appropriate bails to use.  I think I know just what will work, the hard part is finding them...  Wish me luck!