Glass Fusing

@ Creating with a mold that has some texture and depth like this one can be a bit challenging. Our instructors would recommend that cutting 2 layers of glass and fusing them together in an initial firing, then placing the fused glass on the mold and slumping is going to be the most likely way to achieve good results. For slumping, you can use a fairly common schedule with a ramp rate of 200 degrees an hour, the key to getting depth and detail is going to be going to a slightly higher temperature than usual, around 1300 degrees F, but only holding at the top temperature for 5 to 10 minutes before cooling as fast as possible to your annealing soak. Happy fusing, and we sure hope you get a perfect pumpkin plate to enjoy this fall season!

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@curly6 The slightly matte or textured surface is the result of the glass touching the mold. Unfortunately, at the temperature needed to "fire polish" something, the glass is soft enough that it will not retain the slumped shape. For future projects, you can attempt to avoid this finish by reducing the time that the glass is exposed to slumping temperatures. You may wish to set an alarm on your controller for when the kiln reaches the target process temperature so you can check the slump progress and skip to the next (cooling) segment of your cycle. This may help prevent the glass from fully settling into the mold and imprinting the texture of the ceramic mold surface.

I just slumped a very nice 12 inch bowl. The inner surface and edges are smooth and glossy. The outer surface (that went down into the mold) is not looking good. Can I refire so the outer surface is "polished" without disrupting the rest of the bowl?

@bigdogpots There are no absolute ratios that will allow you to reduce the firing temperature and increase the hold time (or vice versa) to achieve a similar fused effect, and in this instance, our fusing instructors suggest that time and temperature are not the most likely culprits causing the devitrification. The first thing to consider or try changing is how you clean the glass before firing. Some glass needs to be exceptionally well cleaned because any oils or residue on the surface greatly increase the odds of devitrification. You can use denatured alcohol, vinegar, dish soap or glass cleaner to break up oils on the surface, scrub the glass well using a soft bristle brush or cleaning cloth, and rinse extremely thoroughly. Additionally, using glass that is tested compatible for fusing should cut the risk of devitrification. If you are using glass bottles, window glass or other non-tested glass, you may find that using a coating of Super Spray or Clear Coat Overglaze will help keep the surface glossy and smooth. I hope this helps you to get the perfect finish on your fused art.

Is there a formula or ratio to figure out achieving the same kilnforming effect at different target temps and hold durations? I have a project that appears have some slight devitrification and would like to avoid that in the future by heating to a lower target. In this case my target temperature was 1260 for .45. What would be the hold time if my target was 1220 to get the same effect?

@ I reviewed your questions with our fusing instructors to ensure I'm addressing all the potential issues. In reference to the devitrification, there are multiple factors that can impact that, not just the firing schedule. Using glass that is specifically tested compatible and formulated for fusing is the first step in getting a gorgeous finish. Beyond that, avoiding using a grinder is recommended as the residue from grinding can sometimes show up as a dingy looking halo. Additionally, when cleaning glass before fusing it is important to thoroughly rinse all cleaning agents off and wipe dry with a clean, lint-free cloth. If these factors are eliminated you stand the best chance of getting beautiful results. For your 1" - 3" cabochons a firing schedule of seg.1 500/h to 1000F with 5 min. hold, set.2 500/h to 1250F with 10-15 min. hold, seg.3 500/hr to 1450F with 10 min. hold, seg.4 Full/h to 900F with no soak/end program is appropriate. The hold at 1250F is commonly called a "bubble soak" and should be longer for larger projects or projects in which you wish to minimized bubble entrapment from textures, frit and more. We can't wait to see what you create!

@jsyorganic Making glass cabochons can be a quick, fun way to be creative. Due to the smaller project size, firing schedules can look a bit different from the schedule you would use for a larger project. Ramp rates can be a bit faster, and soak times are generally shorter or even removed from the schedule. Without reviewing the complete schedule you are referencing it's difficult to say if the omission of a soak time is correct, but I would anticipate that your projects should round out and be fully fused using a schedule with no soak at the peak process temperature.

Hi! I need an advice on the firing schedule. The size maybe 1-3 inches of jewelry cabochon glass stone with 6mm thick. I am curious about the full fuse schedule, segment 4. There is no soak time unlike other firing schedule. Is this correct?

@tiptondf While some artists are able to successfully fire glass in a ceramic kiln, it is a much more challenging process than fusing in a glass kiln. Glass kilns typically have elements in the lids that allow the glass to heat more evenly, whereas ceramic kilns often only have elements around the outside perimeter. Because of this difference, and the difference in firing chamber size it is important to be cautious not to heat or cool the kiln too quickly as the risk of thermal shock is greater in this configuration. Additionally, ceramic kilns are usually designed with a lot of depth for tall artworks and to allow multiple shelves to be stacked. While this is fine for ceramics, positioning multiple shelves for glass firing can create uneven heating and heat distribution. The result of this may be some projects over-firing while others are under-fired, as well as increased risk of thermal shock. To best determine how to use the built-in controller you may wish to reach out to the manufacturer or a ceramic supply business that is more familiar with the operation of the controller as it relates to heating rates in that particular model of kiln. Additionally, there are multiple types of pyrometric cones, and using them to gauge temperature isn't an absolute measure, as style of cones, heating rate and firing time can impact their performance. It appears most process temperatures for glass fusing can be achieved between a cone 019 and 013. You can find more information about cones by conducting a web search for pyrometric cone temperature charts. For more information about preferred glass firing schedules you can visit https://www.delphiglass.com/page/knowledgeBaseView?KBItemID=90