BASIC FUSING GUIDELINES
This guide is to help you get started with your new kiln. For a thorough explanation of the process there are some very good books out there. Two books I recommend are Introduction to Glass Fusing by Petra Kaiser and Contemporary Warm Glass by Brad Walker.
Getting Started: When you get home with your new kiln, you will want to set it up in a suitable work area. Your work area should be ventilated and your kiln should be set up on a non combustible surface and have at least an 18 inch clearance on all sides. Make sure the circuit you plug your kiln into can handle the amperage of your kiln. The amperage your kiln will draw should be stamped on the control box of your kiln. Make sure no other items are plugged into the circuit your kiln uses. Never use an extension cord with your kiln.
Preparing the Kiln Shelf:
Before you start fusing, you must prepare a kiln shelf. A thin layer of kiln wash is applied to the shelf. Most people use a Japanese "haike" brush to apply kiln wash. This kind of brush has very fine bristles that allow the kiln wash to go on more smoothly. You can use a regular paintbrush if you want, but make sure the brush has wide, soft bristles. Foam paintbrushes also work well for kiln washing cool surfaces, but don't use them with hot shelves or molds. Please wear a mask when handling dry kiln wash!
To apply the kiln wash, it's often best to pour a bit of it into a bowl or use a wide mouth ball jar to allow easier brush access. Make sure you shake the kiln wash mixture before pouring, as it settles very quickly. You should also stir the mixture several times while applying to keep all of the particles from settling to the bottom. To brush on the kiln wash, first dip the brush into the mixture until it is fully saturated. Glide it over the item you want to coat, usually a kiln shelf. Glide in one direction and then the other, allowing only the tip of the brush to touch the surface. Apply a thin coat, rather than a thick one.
You should apply at least four coats, alternating the direction of application. Firing the kiln shelf to about 550 degrees F and holding it for about 10 minutes should remove all the moisture from the shelf. When you fire, leave the kiln door propped open slightly to allow the moisture to escape.
Once the kiln shelf is dry, inspect the item to make sure it is covered with a smooth layer. If you want, you can smooth the kiln wash slightly with a soft lint-free cloth. If the item is a mold that will be slumped into, check to make sure that the air holes at the bottom have not been filled by the kiln wash. If they have, just re-poke them. Again, always wear a dust mask when working with kiln wash as the dust is harmful to your lungs.
Also available as a separator is a thin kiln shelf paper called thin fire. It is very convenient but does create some fumes as the sugar binder burns off. Basically you place the thin fire paper smooth side up on the kiln shelf and place your project to be fused on top of the thin fire paper and turn on your kiln. Venting your kiln is recommended when you use this product. After the binder burns out (at about 1000 degrees) you may seal the kiln. Always wear a mask when cleaning up the thin fire after it has fired as the ceramic particles in the residue are harmful when airborne.
Creating your Project:
Let the fun begin!
Choosing your glass:
If you have taken a class or have done a little reading you may know that the glass you are fusing needs to be compatible. Its compatibility is determined by the glass coefficient of expansion (COE). Within the same project all pieces of glass must have the same COE. Most fusible glass will have a COE of either 90 or 96. Bullseye and Uroboros have a line of specific glass with the COE of 90. Uroboros and Spectrum have a line of specific glass with a COE of 96. Each piece of glass you purchase should have a sticker with either 90 or 96 on it. If you fuse a glass project with different coefficient of expansions, the project will have internal stress and likely crack. This is caused by internal stress at the molecular level. As you create your project keep in mind that you need to have a minimum of two layers of glass to maintain the original shape of your project.
Keeping a Log:
As you begin to create and fuse your projects, it is important to keep records of what you have done. This could include how many layers of glass, colors, glass brand, whether they had a clear cap on top, frits, stringers or anything else you may have included in your piece. Your firing schedule should also be kept on this log. This allows you to repeat your successes and avoid your failures.
Slump, Tack & Full Fuse:
Slumping refers to heating the glass enough to allow it to bend- either over a mold or into it. This usually occurs at 1250-1275 degrees F. Tack fusing heats the glass enough to melt the components together and still maintain the original shape. This begins around 1300 degrees F. Full fuse melts the glass completely together usually leveling out at a thickness of 6mm with a smooth surface and occurs at 1480-1500 degrees F.
Fusing the Glass:
As the temperature of your kiln heats up it is important that the glass heats evenly. If the rate is too fast thermal shock occurs and the glass cracks. Smaller jewelry pieces are more forgiving as they heat up evenly with a very quick firing schedule. The actual thickness of the glass has a direct impact on how evenly the glass heats up. You will need to have a slower schedule for larger pieces or those that you have fused once and are being fused again (re-fused). After the temperature goes above 1000 degrees F you may crack the lid of the kiln and peek in without disturbing the glass.
Programmable kilns make it easy to set up a firing schedule at a certain rate. With a kiln that has a manual control switch there are ten settings. You must find the correct number on the dial to control the rate of heating you desire. Remember that these temperatures and rates are approximate. When using a small kiln many times they heat so quickly that the pyrometer is measuring the temperature at the top of the kiln, but at the surface of the glass the temperature may be 100 degrees cooler. You must look in the kiln to see what is going on. With larger kilns there seems to be less disparity in glass temperature and chamber temperature. The larger kilns usually heat slowly and this allows for an even dispersal of heat. Once your glass has reached fusing, tack or slump temperature, it is suggested that you quick cool your kiln to 1000 degrees. This reduces the chance for devitrification. Devit is a crystallization that can occur on the surface of the glass and appears as a scummy dull coating. Some glasses are more prone to devitrification and there are products (Spray A, Clearcoat Overspray or Super Spray) that can be used to prevent or minimize it.
Once the glass has reached the desired temperature, the cooling cycle begins. All glass can be quickly and safely cooled to 1000 degrees. This can be accomplished in a small kiln by cracking the lid. Between 1000 degrees and 900 degrees glass goes through the annealing range. Annealing is the process by which the stress in the glass is relieved and the molecules in the glass are allowed to cool and arrange themselves into a solid, stable form. It is critical that the glass cools in this zone at a certain rate. If the glass cools too quickly stress is created within the glass and this may cause the glass to crack. The annealing rate depends on the thickness and area of glass that is being fired. For many of the smaller pieces you may be fusing, the insulating quality of the kiln bricks should allow the kiln to cool at a rate that will also allow the glass to anneal properly. The lid must not be cracked (this would allow it to cool too quickly).