How to Weave Glass

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We all take things for granted, at least I do.

Nothing points this out more than trying to do something familiar in a new way, or with new materials.

Weaving is an art that assumes the materials used are flexible. Yarn and thread bend easily. People who weave baskets and cane chairs soften the fibers by soaking them. With enough force, metal can be bent and woven. But how does one weave something that is not flexible at all and, if stressed, will break?

Actually, it’s not difficult if you think about weaving in a different way.

Consider a tabby weave where the warp is made up of flexible threads and the weft is rigid sticks. What makes this work is that the warp threads bend up and down, around the rows of sticks. The shape these warp threads take on is a sine wave—remember high-school trigonometry?

Looking at the weaving from the side, the even and odd warp threads form a shape like a continuous row of figure eights laying on their sides, with each weft stick slipped into a hole in the figure eight.

The trick to weaving glass is to think of the weft as a set of sticks that do not bend and the warp as a set of sticks that are pre-formed into a series of curves that fit together to create figure-eight shapes like those in the example above. Once the warp is shaped, it is a simple matter to slip the weft threads into place by inserting them into the holes of the figure eights from the side.

Since glass in its solid form does not bend without breaking, we will use heat to make the glass fluid enough to bend. This is done by heating the glass in a kiln and using forms to shape it while it is in a semi-fluid state.

Project Notes

For this demonstration, I chose to make an eight-inch-square plate of woven glass. Since the weft threads will have a natural spacing between them to make room for the bending of the warp threads, I decided to also space the warp threads a bit apart to create a balanced plain weave.

I made each warp and weft thread out of a piece of soda-lime art glass one-half inch wide, eight inches long, and three millimeters thick.  Although I used soda-lime glass, the process would be the same for any type of glass.  For each plate, I used nine warp threads and nine weft threads.

Note: Many people who weave glass use the round glass rods sold for glass bead making. I use flat glass because I like the results better, and because I already owned a quantity of flat glass.

To cut the glass, I used a hand-held glass cutter, glass pliers, and a straight-edge.

The principle of glass cutting is that you use the wheel of a glass cutter to score the surface of the glass. The glass-cutting pliers have rounded jaws which, when used to squeeze the glass, cause it to break along the score. A straight-edge is useful for scoring straight lines.

Interestingly, once the glass is scored it should be broken immediately. If the glass is left unbroken for months after being scored, it heals enough that the score may no longer break cleanly. This is because, even in its solid form, glass is a bit fluid.  In fact, very old windows that have been in place for a long time are actually a tiny bit thicker at the bottom than at the top.

The photograph below shows the strips of glass assembled into the basic shape of the eight-inch plate I plan to make from woven glass. I use this step to check the pattern and placement of the warp and weft strips.

The next step is to bend the warp glass into the desired shape. For my plate, I decided to use nine warp and nine weft threads. Only the warp threads need to be bent, but they must be bent enough to allow the space required for the weft threads to slip between the layers (in other words, through the holes in the figure eights).

The glass I'm using is three millimeters thick, so I need to make forms that I can place the glass on to create a three millimeter gap. This is easier than it sounds. I use clay to make the forms because it is readily available and can be reused. The trick is to make the forms three times thicker than the thickness of the glass. This ensures that the opening is wide enough to easily weave in the weft threads (remember, they can't bend at all) even after taking into account the fact that the clay will shrink when it is fired.

To make the forms uniform, I used two wooden dowels about nine millimeters thick and a piece of PVC pipe as a rolling pin.

The clay is rolled out by placing the clay on a board between the two dowels. The rolling pin rests on the dowels and forces the clay to reach a uniform thickness. Using a sharp knife, I cut strips about one-half inch wide and about twelve inches long.

Since I’m using nine strips of glass in the warp, I need only five pieces of clay to use as forms—one for each odd number between one and nine. All nine of the pieces of warp glass will be placed on the clay strips. Then, when I do the weaving, every other formed piece of warp glass will be turned over so that the part of the glass that goes up in one row will go down in the next.

Note: I could have done the same thing with four pieces of clay. It is just a matter of deciding whether to work with odd or even side of the sine wave. For an illustration of what I mean, look at the curves in a shaped warp thread. See how there are five bumps on the top and four on the bottom?

After the clay forms have been cut, the clay must be slowly dried and fired before it can be used. I dry the clay between pieces of newspaper with a thick piece of glass on top to prevent warping. Once the clay strips are dry, they are ready to be fired in a kiln. Some of the clay pieces broke during the drying process, but that doesn’t matter because I can repair them with a bit of plaster.

I fired the clay strips at 1900 degrees Fahrenheit, but could have fired them to a lower temperature. The only requirement is that they clay be fired to a little higher temperature than the glass will be fired at, and the glass will be fired at 1200 degrees F.

Once the clay is ready, I used Elmer’s glue to glue each one onto a piece of fiber paper on which I drew an eight inch square. Fiber paper is special paper that contains silica and is commonly used to keep glass from sticking to the kiln shelf during a glass fusing or slumping process.

The fiber-paper square allows me to space the clay strips properly and evenly. Elmer’s glue will burn up in the kiln, but that is not a problem because I’m only using it to keep the clay strips in place on the paper until I get the whole thing into the kiln.

The clay is still not ready to use as a form because the glass will stick to the clay if I don’t do something to prevent that. So, after repairing the cracks in the clay strips, I cover the clay with several layers of kiln wash. By the time I’m done, you can no longer even see the cracks in the clay strips.

Next, I place the clay strips glued to the fiber paper into the kiln and carefully rest nine of the glass strips (my warp) on the rows of clay, placing them perpendicular to the clay strips.

I also placed the weft strips into the kiln on a piece of fiber paper. I do this not to shape them, but so the heat can melt and round out the sharp edges of the glass strips, both to match the look of the warp threads and to make the weaving easier.

I placed little pieces of fired clay (the red bars) around the glass to weigh down the fiber paper. Fiber paper curls as it fires and can reach up and touch the glass, causing a little smudge on the glass, so the clay weights are used to hold it down.

Slumping is a term that describes what glass does when it is heated just enough to become soft and change shape, but not enough melt or fuse. For the type of glass I am using, this requires a temperature of about 1200 degrees Fahrenheit.

Fusing occurs when two or more layers of glass are melted together and become one. For this glass, fusing happens anywhere from 1350 to 1500 degrees Fahrenheit. The fusing process is continuous and must be watched to get the desired amount of intermingling between the two layers of glass.

To slump my warp and create the sine waves, I processed the glass at 1200 degrees Fahrenheit for about 20 minutes. Because glass must be heated and cooled slowly to prevent breakage due to temperature shock, the whole process of ramping up to the slumping temperature and then cooling back down took about eight hours.

The photograph above shows a piece of warp glass that has been bent in the kiln and a piece of unbent weft glass. The two pieces remain the same length despite the bending because the warp-thread strip stretches as it is shaped by the heat.

Once the glass is cool, I wash it to remove traces of the burned fiber paper and kiln wash. At long last I am ready to weave the glass. Weaving is the easiest part of the whole process and takes only about five minutes!

I lined up the nine strips of slumped warp glass on a clear piece of base glass that is eight inches square, flipping over every other piece of warp glass to create the figure-eight spacing. After the warp is in place, I slid the weft strips in from the side. I carefully positioned all of the pieces onto the clear base, using a few drops of crazy glue to keep things from sliding around. Like the Elmer’s glue, the crazy glue will burn off in the kiln. At this point, I have the option to add a few decorative touches to my piece. On the two plates shown below, I have added decorative balls of dichroic glass as an accent.

Note: A clear-glass backing isn't necessary for a woven glass piece. The fused strips will be strong enough to hold their shape after firing. Because I am making a functional plate, however, and because I've chosen an open plain-weave structure, I'm adding the clear base sheet so that small items put on the plate won't fall through the holes in the weaving. The clear plate backing also adds strength to the piece, another important consideration for a functional plate.

This whole thing (woven strips, clear glass backing, and decorative accents) is placed on another piece of fiber paper in the kiln.

This time I want the weave to collapse, fusing the warp and weft pieces together and fusing the woven strips onto the base piece. This time through the kiln, I will process the glass at 1350 degrees Fahrenheit for about seven minutes. Again, due to the need to slowly ramp up and cool down, the whole process takes about eleven hours.

The weaving is done, but my plate is not quite finished yet. Instead of a flat plate, I want to create one with a graceful curve.

The last step is to slump the woven glass sheet onto a mold that has the graceful curve I want to impart to my plate. Such molds are made of ceramic materials and are commercially available from any glass fusing or ceramics shop. Like the clay strips, I cover the commercial mold with a layer of kiln wash to prevent the glass from sticking to the mold during firing.

The fused weaving is placed onto the prepared mold and it goes into the kiln for the third and final time.

Because the glass only needs to slump, it is processed at 1200 degrees Fahrenheit for about ten minutes until it collapses into the shape of a plate with slightly turned up edges.

If you look closely, you can see the clear glass base underneath the weaving.

The woven glass strips are fused to the clear glass base; but because I stopped the fusing process before they melted flat, the strips have a lot of texture and rise above the clear base. Dishes like these make good soap dishes; the soap is held aloft on the woven strips and the water drains down below.

I used a plate mold to shape my woven glass, but any shape could be used. Some people even open the kiln while the glass is soft and manipulate it into shape by hand—using proper tools and safety precautions, of course.

Instead of creating an open weave out of flat strips of glass, I could have used glass stringers (thin strands of glass) or the round glass rods used for making glass beads. Or, I could have made a warp-faced weave by making more warp threads and placing them closer together. You can also weave glass into other weave structures, but this may require more than one set of clay strips on which to shape the warp threads.

If weaving glass sounds like a lot of work, just remember all of the work a weaver does to warp a loom. And the next time you are weaving, be thankful that your threads can bend!

After 30 years working in computer and networking companies, Sally Eyring retired and went back to school to pursue her interest in fine arts and crafts.  Currently she is a candidate for a MFA in Visual Arts at the Art Institute of Boston at Leslie University, with a planned graduation date of January 2010.   Her thesis project involves weaving ethnically inspired headdresses using magnet wire and fine wool yarn.  In addition to weaving, Sally also casts glass, does wood carving, and works with small metals.