Core-Forming is the oldest form of making glass vessels. This was back when people hadn't figured out how to make a fire big enough or hot enough to melt and heat enough of a mass of glass that is needed for blowing. They formed a core of materials like dung and straw and and melted tiny bits of glass around it. The vessels were very small and were used to carry very precious materials.
Now days, you make something that looks like this. I use a high-refractory plaster and cast it onto a bead mandrel.
Next, I carve away until I get a shape That will work for what will became the void space on the inside of the vessel.
I know I've skipped a few steps here, but it's a little difficult to take photos while you're balancing 4 different things in your hands and everything you're holding is about 2000 degrees! So, using a flameworking torch, I take glass rods and simultaneously heat the rod and the core and keep everything turning in my hands like it is on a rotisserie - both hands are doing this at once. When everything has reached the proper temperature, I begin to coil the rod around the core ( like making a coiled clay pot). This roughed-in form is heated and turned until it begins to resemble the above photo. After the form is solid, then you begin the decorative aspect of the whole thing. This could be more layers of different colors (basically repeating the first steps), blobs, dots, swirls, etc...
The key, and difficult part, is keeping the temperature correct. Everything is eyeballed - you need to know what the glass looks like at each stage. The whole thing is annealed in a kiln for about 12 hours to ensure it will not crack. Sadly, some don't even make it to this point. Glass is a very fickle thing!
I'll continue this later...
Back again!
A little more info... It is very hard to find info on core-forming, simply because there aren't that many people doing it. It has gained somewhat of a comeback in Japan, and I have seen some amazing pieces. They have a classic feel, kind of a throwback to the original days of the American glass movement in the 1920's and 30's (Tiffany, Lalique, etc...), but it is still really hard to find images! I like the work because it doesn't have the look of Saturday morning cartoons that SO much American flame working has. Sorry, all you glass people - please don't take offense - but it's just not my style and I think it looks cheap. Just because something is small, doesn't mean it needs to look like a carnival souvenir. The Japanese work has a calm settled feeling to it and you wouldn't necessarily think it was only 4 inches tall, and I love that.
They also seem to make more free-standing vessels, where as Americans tend to make pendant vessels that are strung on a necklace.
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