Wissmach Luminescent glass is popular among kilnformed glass artists, with good reason. The iridescent rainbow coating is beautiful and eye-catching, making it a great addition to many glass projects. Because it is so popular, we wanted to write a tip sheet to help everyone use luminescent glass successfully. We have done many tests with the material to understand what luminescent glass is capable of and how to fire it in a kiln. These tips are guidelines for you to use at home. It is important to remember that each kiln fires differently, and each sheet of luminescent glass behaves differently due to its handmade nature. The temperatures and hold times may vary. We recommend running a small test each time you purchase a new sheet of Wissmach luminescent glass to understand what results you will achieve with your project. Now, let us get started!
What Is Luminescent Glass Coating?
Luminescent is a low-fire coating best used for reverse-fusing projects fired on a flat kiln shelf. A reverse fusing project is fired face down on the kiln shelf. Sometimes, we call glass fusing projects like these design down. There is a reason that reverse fusing with luminescent glass is more successful than firing the coating face up. When a sheet of glass with a luminescent coating is fired in a kiln face up, the combination of heat and oxygen can cause it to burn off. The result can be an uncoated sheet of glass or a loss of vibrancy in the coating. Firing a luminescent sheet of glass face down helps to prevent this burn-off from occurring if fired in a lower temperature range. It is important to note that luminescent glass may still have some degree of burn-off even if fired face down. Reverse fusing is a fun and unique way to think about kilnforming. All the images in this tip sheet are projects created using reverse fusing.
What Temperature Range Works Best For Luminescent Glass?
We have tested a variety of temperatures and hold times using luminescent glass to find out what types of results one can achieve. Firing your luminescent glass no hotter than 1400° Fahrenheit face down during a reverse fuse will yield the best results. Firing your glass hotter than this, even face down, can result in greater degrees of luminescent burn-off. The coating may even burn off entirely. Below is our recommended firing schedule for a reverse fusing project using two pieces of 3mm sheet glass stacked. Make adjustments as needed to the temperature and hold time for your kiln.
| Rate | Temperature | Hold |
|---|---|---|
| 400°F/204°C | 1225°F/662°C | :30 |
| 600°F/315°C | 1400°F/760°C | :10 |
| As Fast As Possible | 960°F/515°C | 1:00 |
| 100°F/38°C | 700°F/371°C | :01 |
| As Fast As Possible | 70°F/21°C | :01 |
Cool To Room Temperature
After I Fire My Luminescent Glass Face Down, Can I Re-Fire It Face Up?
After firing a luminescent piece of glass face down on a flat kiln shelf, it can be re-fired face up as long the second firing is at a low temperature, such as one used for a slump. To best ensure that the luminescent coating will remain on the surface during a second firing, keep your temperature as low as possible to achieve the desired result. It is impossible to give a specific temperature for the second firing. We have had the most success using temperatures below 1250° Fahrenheit, but conducting tests to find the results you want to achieve is recommended.
Our tests have shown the initial face-down firing on a flat surface can often make the coating stronger for future firings, but not always. It’s important to note that each time you re-fire luminescent glass, there is some risk of burn-off or loss of vibrancy. Also, as we mentioned, each sheet does react uniquely, making tests before creating your project essential.
How Many Times Can I Re-Fire Luminescent Glass?
There is no set amount of times you can re-fire luminescent glass. Each sheet will behave slightly differently due to its handmade nature. Also, the temperature and hold time during subsequent firings may cause more or less burn-off.
Can I Lay Papyros Paper Or Fiber Paper On Top Of The Coating To Prevent Burn-Off?
Laying Papyros or fiber paper on top of a face-up luminescent glass project during kiln firing can help prevent burn-off or loss of vibrancy. It also may not. Our tests have shown inconsistent results using these materials. If this works for you in your kiln, keep using it. Given how each kiln fires differently, we cannot recommend using these techniques to yield a consistent result. The most consistent result we have discovered is to fire the luminescent glass face down of a flat kiln shelf no hotter than 1400° Fahrenheit. Laying Papyros paper on the kiln shelf between it and the glass does offer the same protection as a primed shelf when firing the glass face down.
Can I Cap Luminescent Glass With Glass To Prevent Losing The Coating?
Capping the luminescent coating will cause it to disappear.
We hope these tips provide insight into how to work with luminescent glass in your kilnforming projects. As we mentioned, they are only guidelines. We recommend performing tests with each new sheet of luminescent glass in your kiln. Wissmach Luminescent is a beautiful addition to any fused glass project. By understanding how it behaves, you can use it to create countless works of glass art at home without losing its lustrous rainbow shine.
If you have ways that you enjoy working with luminescent glass, we would love to hear them!
Happy Kilnforming!
-Drew Kail, Wissmach Kiln Consultant
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