Most of my blown work involves the use of applied components. What this means is that I sculpt little flowers, leafs, what-nots and do-dads ahead of actually making the blown piece. I like to do it this way because I am allowed to examine the components after they have cooled and make well thought out decisions as to final placement. Sometimes I can spend days just making these small things.
This is where the Bowl In Hole technique can come in quite handy. It allows me to get a days work done without the need of having the furnace running. It also is a spiffy way to melt other types of glass not compatible to my Spectrum Nuggets base glass. Recently a friend of mine opened a glass blowing studio, and he melts Spruce Pine Cullet. Since these two types of glass don't play well together, he was nice enough to give me a small bagful to take home where I utilized the Bowl In Hole technique.
To start with, I much prefer to use soup bowls over coffee cups. The wider opening along with the bowl shape resembles an actual crucible and is much easier to work out of compared to a coffee cup with straight walls and a flat bottom. Plus, If your going to go thru the process of doing this, a soup bowl yields more glass.
Begin with a clean bowl and clean cullet. Fill the bowl to the rim and place it in the kiln or annealer. Check the position. Your going to have to transfer it hot and full to the glory hole, so make sure you can grip it without dropping it. My small kiln opens from the top so I propped the bowl on one side to create an angle where I can pick it up with tongs. By 'tongs' I mean log picker-upper things used in fireplace sets.
Also, the glory hole may need some sand or grog mounded up/dug out to make a nest for the bowl to set into. I like to situate this nest area to the rear of the the glory hole behind the burner. This way it's out of the way while working. Having the bowl tipped slightly toward the doors will make gathering easier. Some folks like to make the nest toward the front, behind the doors. This way it's easier to gather out of. To each his own. Just don't place the bowl directly in front of the burner. When you have everything set up on both ends try a cold run to make sure all goes smoothly before it's all hot.
Once the bowl is positioned in the kiln, mound up a few more pieces of cullet in the bowl because as the glass melts, the air pockets will shrink and the bowl will wind up only about ¾ full. Ramp up the temperature of your kiln 500 degrees per hour to 1000 degrees, then go full speed ahead to 1300 and hold 15 minutes. At this point, make sure you have heated up the glory hole good and hot. You DON'T want to put the hot bowl in an unheated hole. Turn off the glory hole and place the business end of the log tongs in the hole to warm them up. Then, swift like a fox, and quick as a bunny, transfer the bowl to the hole, and fire it right back up. I have heard other folks using faster schedules to get the glass preheated. My thoughts on this go back to the Haste Makes Waste theory. Having no idea what the bowl is made of, I prefer to be safe over sorry. No sense cracking the bowl. One way to move things along is to set the bowl up in the kiln the day before and utilize the kiln controllers delay setting. Increase the hold time, and your bowl will be hot and ready for you when you walk into the studio in the morning.
I tried a few different shots, but it was too bright in the glory hole to see the bowl, but trust me - it's in there!! The glass will be all melty in a short time, but will have lots of air bubbles. It takes about 2 hours for the glass to fine out. I use his time to make components from my furnace glass. Or clean up around the studio. Or do some grinding/coldworking. Or something. There is always something to do.
Once the glass is good to go so are you! Work as usual until the bowl is empty. When it is, preheat the log tongs, remove the bowl and toss it in a bucket of water for a fun steam show, or place it in the annealer and *maybe* you can use it again. This is an iffy thing to do at best. At this point the bowl is stressed and could crack the second time around making a mess in the glory hole or your kiln. I don't think it's worth it. Just hit the thrift shop for some new bowls. But check out the picture below - I went for the fun steam show and the bowl still didn't break! Go figure. So I took a picture of it. On the left, notice where the grog stuck to the glaze - you will see the angle it was sitting at in the hole. The right hand picture shows how much the glass flattens down after it turns to a liquid, and the small 'heel' left behind.
Pictured below is the work created from a bowl of glass - enough flowers, leafs and stringers to decorate a fair sized blown piece. On the lower left are some clear leftovers from stripping the casing, so I saved it to re-melt. As I said before, these were made using Spruce Pine, and they are headed with me to my friends shop to make something larger than I can make here at The Shack.
It's going to be a blast. :)
The piece has since been made. Here is a short video of the final assembly.