The Fused Glass Coaster Project
This project, which involves making glass coasters, is an excellent first fusing project. It assumes that you have either successfully tested your glass for compatibility or have obtained "tested compatible" glass. It also assumes that you have properly kiln washed and prepared your kiln and kiln shelf for firing. If you're not familiar with these topics, spend some time reading through our glass tutorial.
For the coaster project you will need a pen and some blank paper, a glasscutter, a working kiln, some kiln wash or fiber paper, and about half a square foot of glass for each coaster you wish to make. You can choose any glass colors and textures you like. Note also that a "coaster" and a "glass tile" use basically the same process. The bottom of this page has some specific information about glass tiles.
The major steps in this project are:
DESIGNING THE COASTER
The design for the coaster can be as simple or as elaborate as you would like. If you have experience with cutting glass, you can come up with a design that gives you the opportunity to show off your cutting skills.
If you’re new at glass cutting, you can make a very simple design that uses mostly straight lines. If you don’t want to try your own design, you can use a copyright free stained glass pattern or just modify one of the design ideas shown on this page.
If you prefer, you can make your design using a sheet of paper. Graph paper works best, but you can use any kind of paper. Draw a square on the paper the size of the coaster you wish to make. Three and 3/4" sides work very well, but you can use any size that seems right to you.
Sketch your coaster design inside the square. Don’t worry if your design isn’t perfect. Frank Lloyd Wright didn’t design a masterpiece the first time out, either. The key is that you start to think about the different colors and types of glass that are available and how they can work together.
Several sample coaster designs are illustrated on these two pages Feel free to use any of them and to adapt the colors and lines as you see fit.
All of the coasters use at least two layers of glass, with the bottom being a solid square. In some cases a few design elements are placed on top of the second layer. Often a dark opaque glass is used for the solid layer on the bottom (called the "base" layer), but you can pick other glass colors and types if it fits your design concept.
CUTTING OUT THE GLASS
If you are familiar with stained glass work, then this phase is similar to working with any stained glass pattern, with one major exception. Most fusing projects require two (sometimes more) layers of glass, rather than the one characteristic of stained glass work. This isn’t as complicated as it sounds, however, since one of the layers is usually a single color.
For many fusing projects, clear is frequently selected for this "base" layer, but other glass of any shade can be used. For coasters, the base layer is often a dark opaque glass.
You should cut the base layer about 1/4" smaller than the top layer so that the top layer overhangs the base layer by about 1/8" all around. (For example, the base layer would have 3 1/2" sides if the top layer had sides of 3 3/4".) If the coaster is properly fired, this overhang will melt first and curve around the bottom layer, creating nicely rounded edges
If you’re already experienced in glass cutting, you may go ahead and cut out the pieces of the design you created in the design step. If you’re not familiar with glass cutting, then it’s a good idea to first practice cutting with a piece of scrap glass. Any good book on stained glass techniques will contain a section on glass cutting.
By now you should have designed your coaster and cut out the glass. You should have also prepared the kiln for fusing by applying kiln wash or deciding to use fiber paper. You’re almost ready to load and fire.
But wait. Before you can load the kiln, you need to make certain the glass is clean. Washing with clean water is sometimes sufficient, but you may need to use dish washing liquid or a commercial glass cleaner. Since some commercial glass cleaners have a tendency to leave a haze on the glass, many glass artists prefer to use denatured alcohol or acetone to clean their glass. Whatever you use to clean the glass, make certain you remove any smudges or residual oils.
When you’re finished cleaning the glass, take time to dry each piece with a lint-free cloth - from this point on you should wear latex gloves or handle the glass only by the edges. Avoid getting fingerprints on the glass - they will show up as dark smudges in the finished work.
Now it is time to assemble the glass on a kiln shelf that has been protected with kiln wash or fiber paper. It doesn’t matter if the shelf is inside the kiln or outside. Do whichever is easier for you, but if you assemble the project outside the kiln you will need to be careful not to disturb it when you return it to the kiln.
Start by placing the base square of glass in the center of the shelf. Next, place the second layer and assemble any patterned elements on the top layer. The pieces should overhang the edges slightly - about an eighth of an inch (3mm).
If one of your pieces does not want to stay in place, consider using a dot of glue (ordinary white glue will work) to hold it until you can transport the piece to the kiln. Don’t use glue to counteract gravity and hold pieces in place in unnatural positions (the glue will burn off before the glass fuses), but a small amount of glue can help avoid unwanted shifting as the glass is loaded into the kiln. If you're using a general purpose glue (such as Elmer's), it’s generally a good practice to dilute the glue 50-50 with water. Use as little glue as possible. If you can get by without the glue, you should.
Once you are satisfied that the pieces of glass are positioned in place, it is time to get ready to fire. If the shelf is not already in the kiln, carefully load it into place, setting it on top of the kiln posts which should already be sitting on the floor of the kiln.
Once the kiln is loaded, you should take a moment to make the proper entries in your firing log. You should keep the information that seems most important to you, but at a minimum your log should include the date, a description of what is being fired, and information about the firing schedule used.
For this initial fusing firing, we will use a very simple, straightforward schedule that’s appropriate for two layered pieces of art glass up to about nine inches in diameter. The major steps follow below.
Please note that these temperatures are for average kilns and typical glass types - your kiln and materials may require you to adjust the temperatures and times slightly up or down.
• Begin firing the kiln.
Let the temperature increase evenly, at a rate of about 600 degrees F per hour.
• Slow down to reduce bubbling.
When the temperature reaches about 1100 degrees F, slow down the ascent to around 250 degrees F per hour. An aggressive firing schedule eliminates this reduction and continues firing rapidly, but going more slowly through this temperature range will reduce the likelihood of excessive bubbling of the glass at higher temperatures.
Once the temperature reaches 1300 degrees F, you can turn the kiln up and fire to your full fusing temperature as quickly as your kiln allows.
• Heat to full fuse and soak.
Once the kiln reaches full fusing temperature, you should maintain that temperature and soak the glass until a full fuse is achieved. If your kiln has a peephole, check on the piece to see if fusing is taking place. The edges should be fully rounded and the pieces on the top layer will flow together.
For two or three layer items like the coaster, Bullseye recommends a 10-minute soak at 1500 degrees F. Spectrum recommends a 10-minute soak at 1450. Uroboros suggests a one-hour soak at 1450. You’ll need to find the temperature and soak time that works best for you and the way you work.
For float glass, your full fuse temperature will be higher than the temperatures recommended by the glass manufacturers mentioned above. Try soaking for ten minutes at about 1575 degrees F and adjust if needed.
• Flash vent.
Flash venting is not required for many types of glass, but most fusers employ the technique to quickly drop the temperature from full fuse to just above the annealing range. This helps minimize the risk of devitrification and also speeds up the firing a bit, but care needs to be taken when you flash vent to ensure that safe procedures are followed.
With gloves and safety glasses on, open the kiln door and allow the heat to escape from the kiln. Be careful to avoid the rush of hot air that often accompanies the first opening of the kiln.
Ideally, you should vent the kiln until the bright red starts to fade and color begins to come back into the glass. You want to allow the temperature to drop to just above the annealing zone. Venting to around 1100 degrees F works well for most glass.
Another method often used is to open the kiln door, count to eight, then close the door and check the temperature. If necessary, the door can be opened again and the process repeated until the temperature falls below 1100 degrees F. If the door handle becomes too hot to hold or if the heat seems extreme, simply close the kiln and wait a few moments before trying again.
When you’re finished flash venting, gently close the door. If you want, you can leave it propped open slightly until 1050 degrees is reached, but make certain you shut the door by that point. (For float glass, stop rapid cooling at 1100 degrees.) The temperature will increase a bit from residual heat when you first close the door, but soon it will level out and begin to drop again.
Many kiln manufacturers will recommend that you turn off the kiln anytime you open the door. This is excellent advice, but it is often ignored when flash venting. The reason to turn off the kiln is to prevent electrocuting yourself from accidentally touching a kiln element while electricity flows through it.
Some kilns automatically prevent this by cutting power to the elements when the door is opened. If your kiln doesn’t do this, the safest thing to do is to power off the kiln any time you open the door. Alternatively, if your kiln has a controller, you can program it not to fire during flash venting.
At 1050 degrees Fahrenheit (1100 degrees for float glass) begin the shotgun annealing process. Control the temperature drop to no more than 200 degrees F per hour (about three degrees F per minute). This rate of temperature decrease is very conservative and will ensure that your coasters are fully annealed.
Also, by annealing over a wide temperature range you can be certain to alleviate the stress in the glass. For shotgun annealing, it’s generally recommended to anneal from 1050 degrees down to 750 degrees. This range is wide enough to account for most types of glass. (For float glass, you may want to start the annealing schedule at 1100 degrees F.)
• Cool to room temperature.
Once the temperature falls to 750 degrees F, annealing is complete. You may let the glass slowly cool to room temperature. For two layer projects the size of this one, you will avoid thermal shock if your kiln cools no more rapidly than around 500 degrees F per hour. If it cools faster than that (most kilns don’t), you will need to fire lightly from time to time to slow down the temperature decline.
• Inspect the coaster.
Inspect it for uneven edges, rough spots, or other problem areas. Note anything unusual or significant in your log.
The most common problems experienced with simple fusing firings are:
• Uneven edges - These are caused by overheating, under heating or poor cutting. You’ll need to smooth the edges with a grinder and re-fire to about 1200 degrees to get them to round properly.
• Unwanted bubbles -- Many different factors can cause this, but the most common is probably firing too fast.
• Cracked glass - This is usually caused by either firing or cooling too fast or using incompatible glass.
The key to long lasting glass projects is good annealing. When you hear of a glass bowl or plate that "just cracked" or an item that broke when barely touched, it’s almost certainly a case of not being properly annealed. While it’s not recommended, a well-annealed, relatively thick glass piece is about as durable as ceramic ware, and can withstand fairly rough handling and even occasional drops. The thinner the glass piece, of course, the more gently it needs to be handled.
Cleaning a finished coaster or similar item is simply a matter of wiping occasionally with a damp cloth. Mild cleaning solutions can also be used if desired, but water is generally sufficient.
Sometimes the bottom of the coaster will have a rough surface that can scratch the top of the table it sits on. To prevent this, cover the bottom with felt or use small rubber bumper cushions in each corner. These cushions, which are often used to protect framed artwork from damaging the wall, are available from many framing supply outlets.
If you can make a coaster, you can make your own fused glass tiles. Although not recommended for surfaces like countertops or floors that receive a lot of wear and tear, glass tiles can be a welcome accent for kitchen backsplashes, tiled shower enclosures, or decorative panels.
It’s also possible to inlay fused glass tiles in furniture or wooden boxes, set them in concrete to make stepping stones, or use them as decorative kitchen trivets. The possible uses are limited only by your imagination.
Factors to consider when making glass tiles include:
• Thickness. Two layer thickness works well because the tiles will emerge from the kiln virtually the same size as they entered. However, if your tiles are being used alongside regular ceramic tiles, you should build up the tiles to be the same height as the particular ceramic tiles you’re using.
• Opacity. Because tiles are often grouted on the bottom (like ceramic tiles), it’s often a good idea to hide the tile adhesive by make the bottom layer of glass opaque, rather than transparent. Using transparent glasses for other layers can help give the tile a depth and shine not possible with ordinary ceramic tiles.
• Bottom surface. Some artists suggest that you deliberately texture the bottom of the tiles to make it easier for the adhesive to adhere, but this is not really necessary if a good tile adhesive is used.
• Size and shape. Don’t confine yourself to a single size. Try different sizes and shapes other than square tiles. Narrow strips, triangles, and rectangular tiles can work in the right location.
Tiles can be made more interesting by gluing them to a mirrored surface (use silicone or UV glue), tack fusing a textured design to the surface, or sandwiching your design between the layers. Try sprinkling frit, confetti, or shards on the top surface for a unique decorative effect.