When I got into doing fused glass I had absolutely no interest in slumping bottles. Then a friend gave me a magnum bottle of sparkling wine in a very pretty bottle. I wanted to slump it for her as a thank you gift. I ordered slumping molds and got to work.
I had been playing with smashed beer bottles for a while and each time I ended up with devitrified glass. I knew that I needed to do a lot of testing on other bottles before I did the big one. Since I don't drink wine I called on some friends for a good supply of bottles.
Here's my first test with clear bottles. Clear glass is the easiest to work with. I have 2 molds. One for regular size bottles and one for magnums but I can do regular bottles in the magnum mold. This one was a failure.
When I talk about devitrification this is what I mean. It's when the glass turns permanently cloudy. Glass is amorphous which means that in it's non-liquid state it is not orderly like crystal. Devitrification means that the glass has taken on crystal state and now has this type of surface. It's caused by the speed of the heating or cooling of the kiln in the segments just before it reaches target temperature or just after reaching target temp but before annealing.
The other glass has spikes on the edges and that means that I had the temperature too high. I adjusted the kiln program and tried again.
In this program I did 3 pieces. The clear bottle was fused flat with a bar under the neck, the beer bottle was done flat and the green bottle in the small mold.
The clear bottle fired perfectly. I like the little bridge on the neck which gives it a nice holding spot of you are cutting cheese on the surface. I also like that the embossing on the glass stayed through the firing.
The beer bottle slumped perfectly so maybe I've solved my brown glass issues. The green bottle slumped nicely and there's no devit but the edges were still a little rough. I was able to grind them off for this piece but I needed to drop the top temperature in the kiln a bit.
Next I did a green bottle and a dark green bottle. It looks like it's a mix of green and amber glass. Look how pretty and shiny they are!
Look at that beautiful edge! Now I was ready to do the big magnum bottle.
You can see how big that magnum bottle is. It's also very thick glass. I was glad to see that the painted "J" label stayed on the glass but both bottles have devitrified.
I'm really bummed about this. I'm wondering if the heavier glass needs and even faster ramp down rate. I did give this to my friend anyway (along with that blue and green plate that I shared 2 weeks ago. She has 2 more of these bottles so once they are empty I know she will let me try again.
Here's the interesting thing. I was surprised that the small bottle also devitrified which made me think that the big bottle absorbs so much heat that it affected the temperature in the kiln. I'm not sure if that's the case bit I ran one more cycle using the same program and another bottle just like this one. In that firing the bottle slumped perfectly.
I think I'm done with bottles for a while but if I had known how much slumping bottles would have helped me develop kiln programs I would have done that first. The bottles are free and a great way to get to know the kiln.