How to Do a Vitrigraph Pull -or- How to Play With Molten Glass

In this Instructable, I will show you how to setup a Vitrigraph (Vitri= glass, graph=write, to write with glass). This technique is a fun way to manipulate glass that doesn’t use a torch or crucible to melt it. The results can be used in glass fusing, glass bead making, or any other way that might be interesting to you!

Step 1: Ingredients

Small Flower pot made in Italy (found at hardware store)
Compatible glass
A small kiln with layers that can separate, or a kiln specifically used for Vitrigraph
Kiln temperature controller
Permanent marker
Box cutter
Hammer
Heavy leather gloves
Eye protection
Round file
Needle nose pliers or similar
Long tweezers (12” or so)
Diamond shears or a cheap pair of scissors
Clothes made of natural fibers

Step 2: Disclaimer

This technique has been successfully used in many glass studios. It consists of “playing” with glass hot enough to move, which is about 1650 degrees Fahrenheit. Even when the glass is no longer glowing, it is still painfully hot. I highly advise that you don’t touch it. I am not responsible for any damage that you do to yourself or others. With that said, if you burn yourself, hold the burn under cold water for at least 5 minutes, and then use your favorite burn remedy. I suggest either lavender oil or healing clay of some variety.

Step 3: Prepare the Flowerpot

Some ingenious soul realized that instead of buying a crucible with a hole in the bottom, one could use a ceramic flowerpot for single use glass pulls. Use the size that will fit in your kiln, I used the smallest size available at Lowe’s, roughly 4” or so. Make sure that the tag says “Made in Italy” because the clay used has less possibility of breaking. Avoid pots with any cracks, because the cracks will widen, possibly letting out molten glass and ruining the kiln.
Widen the hole in the bottom with the rough round file. These can be purchased at Harbor Freight for cheap. I made my hole about ¾”. Rasp from inside and outside, only pushing down on the rasp when on the away stroke, and then clean out the pot of any red dust. Don’t breath the dust, because it has silica in it = bad for your lungs.

Step 4: Fill the Flowerpot With Glass

If you plan on re-melting the results of this technique with other glass, make sure you use a compatible glass. Glass is rated by how much it expands, called Coefficient of Expansion, or COE. Glass rods that are used to make beads are anywhere from 33 COE to 104 COE, with other common numbers being 90 COE and 96 COE. This guide is NOT for 33 COE called borosilicate glass, typically used in scientific apparatus. Borosilicate needs a much higher temperature to start moving, and then will move slowly, and cool quickly. Bottle glass is anywhere from 80 to 92 COE, and every bottle can be a different COE, even if they are purchased at the same time. The safest glass to use is likely Bullseye tested compatible, but if you just want to play, one cleaned wine bottle will give you enough glass to fill a flower pot plus extra. You should remove the label and as much adhesive as you can.

To safely break the bottle, wrap it several times. I used a handy Ikea bag and a huge tshirt. With eye protection on just in case, hit the bottle through all of the wrappings with a hammer. My wine bottle was surprisingly thick and hard to break, and I used a small sledge hammer. It took 5 blows, but when it finally did break, it was quite satisfying. It is loud hitting it with the hammer, but rather dull sounding when it finally goes. Carefully unwrap your broken glass bottle, and then with “dull” slow fingers, carefully arrange the broken glass in the flower pot as dense as possible. Take a relatively larger piece and set it across the hole in the bottom to prevent small shards from falling out. Vibrating the pot settles the glass so you can fit more in.

Step 5: Prepare the Hardibacker

You will need to cut the Hardibacker (cement board found in the construction or tile area at the hardware store) to get it to the appropriate size. This stuff cuts similar to sheet glass. You score all the way across, and then snap it. Measure out the bottom of the kiln, and mark two squares about that size next to each other. Run the razor blade on the long line all the way to the other side of the Hardibacker a couple of times. Line the cut up with the edge of the table and break it off. For the thicker Hardibacker, I ended up standing on top of the table and kicking it to get it to break. Worked great! Now use the same technique, breaking the long skinny piece into 3 parts, two the size you want and the third as excess.

Guesstimate the center, and make a hole about 1 ½” across. I used the flowerpot to measure where I should put the hole, the marker to copy the inside hole, and drew a larger hole around the marker outline. Next, carefully cut with the box cutter on the line, just to break or score the surface. Use the hammer to break the hole out. Punch it out from both sides, and use the box cutter to clean up the edges of the hole. It doesn’t have to be perfect, just not too big or small. Too big and your flowerpot could fall through, too small and it will touch the glass coming through.

Step 6: Prepare the Kiln

I am using an AIM 84BD Bead Kiln that has layers that can be separated. I am only using the lid and the kiln ring that has the heating elements (the curly wire) in it. There are kilns sold specifically for this technique, and if it something that you are very interested in, look them up. I’ll use the kiln that I have, since they aren’t cheap. The Hardibacker is used to make an alternate bottom for the kiln. Use the thickest that you can find. The first time I did this, I used a single ¼” board, and I was worried about the hot flowerpot full of melted glass dropping through the bottom because of how badly it cracked. In my second attempt I used a double layer of the ½” Hardibacker, and both layers still cracked, but not as much.

My school, Utah State University, happened to have these handy metal brackets on the wall to use as a shelf. Since we are pulling molten glass out of the bottom of the kiln, it needs to be off of the ground, and not have the bottom blocked. It is best to do this over a cement floor, since the glass can break and send hot glass skittering to unintentional places. It is important to have it very secure, including the plug/extension cord. If the plug/extension cord is anywhere that it could be tripped over…TAPE IT DOWN…you don’t want the whole kiln pulled off of the shelf while hot and live with electricity. Molten glass is conductive, not to mention the huge mess and possible personal damage that it could do.

I used two steel angle irons and two kiln bricks to prop the kiln on top of, and the extension cord runs along the wall out of the way of foot traffic. I highly suggest the kiln bricks as support across the bottom of the Hardibacker. I am fairly sure they are the only reason that I did not lose the first pot to the breakage of the thin Hardibacker.

Stack everything together. My stack = angle iron on shelf brackets, two kiln bricks set perpendicular on the angle iron with a gap large enough to pull the glass through between them, two pieces of Hardibacker with the holes lined up and centered on the gap between the kiln bricks, the flowerpot full of glass centered on the hole, the kiln ring with the elements, and the lid. Make sure that the flowerpot and the glass are not touching the lid because it will end up sticking and eating into the kiln brick of the lid.

Step 7: Extension Cord Safety

A word on extension cords. If you use one, it needs to be rated for the amperage that your kiln is rated for. I am using a 10 gauge 20 amp rated extension cord. Be aware of where you are plugging it into. Most house outlets are rated for no more than 30 amps, if you go over the rating you could throw a breaker or start a fire and older houses may be rated for less. Do not overlap your cord; it can get hot, especially where the plug ends connect.

Step 8: Bring the Heat

Now that everything is safely situated, and the kiln has the temperature control unit connected to it (varies depending on manufacturer, but the kiln gets plugged into the box, and the box has a thermometer type of thing that gets stuck into a special hole in the side of the kiln, and the box plug gets plugged into the wall/extension cord if you need it), make sure that you aren’t wearing any synthetic clothing that could melt onto your skin if overheated. Yowch!

The heating schedule that we need to go by is:
Raise 425 degrees Fahrenheit every hour to 850 degrees Fahrenheit
Raise the temperature as fast as possible to 1550 degrees Fahrenheit to avoid devitrification* of the glass

This takes me about 2 and a half hours.

*Devitrification is when crystal growth happens on the surface of the glass, making it cloudy and in general is not desirable.

Step 9: Pull Out Hot Glass –or- It’s Getting Hot in Heeerre, So Pull on Some... Glass?

Once the kiln gets up to 1550 degrees Fahrenheit you can start testing the glass. With eye protection and heavy leather gloves on, use the needle nose pliers and attempt to grab onto the cooler plug of glass sticking out of the bottom of the flower pot. Raise the temperature slowly (letting the heat soak in for 10 minutes every 25 degrees you raise the temperature), until you can grab and squeeze the cooler plug and pull the glowing glass down.

1600 to 1650 is about as high as you should be going, but up to 1700 is okay. Keep in mind that it takes time for the heat to soak through the glass mass. In other words, if you ramp up the temperature too fast, say from 1550 to 1650, the glass on the top is going to heat up faster than the glass on the bottom that is exposed to the colder environment outside of the kiln. Once the heat starts soaking into the colder lower mass, it will start to move, and then start moving faster and faster, out of control since the glass on top is already very hot. If the glass ever gets too fast, lower the temperature on the controller, and if it is really out of control, you can quickly lift and replace the lid of the kiln to flash cool. Be Careful if you decide to do a flash cool, hot air rises quickly and can burn your arm or face off in the process. The kiln lid will be really hot as well, so have on protective gear.

Pulling the glass out faster will make it come out thinner, slowing down will make it come out thicker. You can use various tools to manipulate the glass, I chose two long tweezers because they were easier to manipulate with the heavy leather gloves on.

Pay attention to where the hot glass is, and it is all hot! It is easy to get carried away and twist the glass up close to the gloves or your arms. Even if it is not glowing, it is over 900 degrees, and can still give you a wicked burn.

Step 10: How Do I Get This Thing Off???

When you want to separate the piece that you have been manipulating from the main flow of glass, use the diamond shears or plain cheap scissors to cut into the glowing mushy part of the glass. It might take a few chomps to get the job done. Make sure that your hot glass sculpture is balanced and controlled so that when it is suddenly released from being held up by the flowing glass, it doesn’t swing around and burn you or somebody else. Gently set it down on either more Hardibacker or wet wooden boards.

Step 11: Finishing Up

Once you start to get to the end of the hot glass, the flow will turn into a tube. Once the center glass that you have been pulling from is gone, only the side glass is left to feed into the pull. You can wait to let the glass from the sides of the pot feed into the pull, but eventually you will keep breaking the tube of glass, and will no longer be able to pull it. Every time you break this bubble teeny tiny shards burst off into the air contaminating your airspace, and adding teeny tiny cuts to your lungs if you breathe it in. Once it gets this thin, stop breaking it, turn off the kiln, and let it cool with the lid on, overnight.
You may be able to handle some of the glass that you pulled; it might be cool enough not to burn when picked up. Use your discretion, and hover your hand over anything/lightly touch before committing to the full pickup.

Step 12: Glass Breaks

You may notice tinking sounds of glass breaking. This is because of thermal shock. The glass on the outside is shrinking very quickly when cooled, and the glass on the inside is still hot. Once the inside glass starts cooling, it pulls on the outside glass trying to shrink, and if the stress is too great, *POP* it breaks into a couple pieces. The thicker the piece, the more likely it is to break.

Step 13: Miscellaneous Information

Decide how you want to use the glass. If it something that you want to keep around for a while in its’ present form, you will need to anneal it so that the inside stress will be minimized. Annealing is when you control the rate of cooling so that all of the glass cools down at the same time. The type of glass and thick it is will dictate what annealing schedule you should follow.

For bottle glass=
Soak at 1030 degrees Fahrenheit for 20 to 30 minutes, then lower by 100 degrees per hour to 700. Turn off the kiln and wait overnight to open. The glass may still be hot even overnight. If it is, take off the kiln lid and let it air cool until you can touch it. If it is too warm and you pick it up, it can still thermally shock and break, possibly cutting you, so wait till it is cool.