Friday, February 17, 2017

Crack the Case –Your Guide to What Went Wrong Inside Your Kiln

Mystery and magic attract us to glass fusing. It’s the mystery of making something new and the magic of melting materials that hook us. I’ve asked numerous students, and most admit that opening the kiln after firing is their favorite part of fusing glass. We look forward to it with the same childhood glee we have when opening a crisply wrapped gift. 

When the project comes out as expected, or sometimes even better, angels sing, unicorns exist and a rainbow glows brightly over your studio. On the rare occasion that the project doesn’t come out well, our disappointment is heartbreaking. We ask why, what was different, where did I go wrong? We rack our brains looking for answers. 

All the while, the answer is right there in front of you. 

You just have to recognize what your broken glass is telling you. 

Let’s take a simple project and break it. Our sample project is made of two full layers of glass, plus an accent layer. The base layer is clear and the second layer is a pretty purple and the third, partial or accent layer is a pattern glass with hints of purple.

To better understand why glass breaks, let’s do a little review. 

There are two basic stages to the firing process: heating and cooling. During heating we take the kiln from room temperature to 1200° - 1500°, depending on the type of fused effect we want. Glass is sensitive to temperature change between room temperature and 1000°. To avoid thermal shock, which is breakage due to rapid temperature change, we heat the glass slowly from room temperature until we reach 1000°.  

Over 1000° we can heat the glass quickly to the desired temperature. At 1265°, the glass will slump and take on the shape of a mold. At 1365° glass sticks together, otherwise referred to as tack-fuse. At 1565°, the glass will completely melt into one smooth piece. This is considered a full fuse. (These are System 96® temperatures.)  

Once we have the desired effect we cool the glass. The process of heating the glass causes stress within the project. We relieve the stress by holding the glass at an annealing temperature for a period of time. This allows the glass in the project to equalize at that temperature. (The System 96® annealing temperature is 960°.) 

After fusing, during the cooling phase, the glass is sensitive to temperature change from 1000° down to room temperature. And the project now has greater value because it’s almost done. To avoid breakage due to thermal shock, after the annealing hold, we slowly cool the glass down to room temperature. 

Read between the lines. 

Heating Breaks

This is an example of what a break would look like if the glass is heated too quickly. The clear base layer and the purple layer broke in two on the way up. They’re visibly separated on the kiln shelf. Yet the accent layer bridges the crack and the project is indeed fused and held together by the accent layer. Layers one and two break because they are larger and therefore have more mass. The greater mass is more sensitive to rapid heat. The accent layer is smaller, less mass and therefore remains intact. A break like this happens inside the kiln. This is a prime example of breakage due to heating the glass too quickly. 

It’s possible to break the project apart and refuse it slower, but the finished product will likely be different from the original design.      

The fix: slow down. Heat the glass at a slower rate. I heat projects from 4” coaster size to 12” bowls at a rate of 300° per hour with dependable success.  

Cooling Breaks 
An annealing fracture has a very specific look. It has a tight curve that rolls into broad gradual curve. (It almost looks like a smile, but not one that any of us would look forward to seeing.) The broad curve is followed by another tight curve. In my experience, the break usually runs vertically through the project. The glass pieces have been fused together and the break is clean through all three layers. The two broken pieces are generally separated by a sizable gap. The gap is evidence of the internal stress in the fused glass. An annealing break can occur inside the kiln or weeks later. This type of break is the result of rushing the annealing time, peeking into a hot kiln or from opening the kiln too early and chilling the glass.

You can re-fire the broken glass and re-anneal it but the finished project may have a visible scar where the glass was broken. You can add frit or extra accent pieces to hide the seam. 

The annealing temperature for any specific family of fusible material is constant. The length of time a specific project needs to be held at that temperature is determined by the size of the project and the number of glass layers used to make the project.  A large project, like a 12” bowl, will require a longer anneal time then small project like a 1” pendant.  

The fix: consult the glass manufacture’s firing guides and be sure to include the appropriate annealing temp and time in your firing schedule. Here’s the hard part. Don’t peek! Or open the kiln below 1000° until it is at room temperature. I anneal projects that are 12” is size or smaller, made with two layers of glass plus an accent, like the example here at 960° for 40 minutes. 

Incompatibility Breaks 

Compatibility breaks are really upsetting because they’re so easily avoided. We do our best to sort and organize our glass by COE, but sometimes a mix-up results in a mystery break. Knowing what to look for can save you from having any future accidents. 

C.O.E. (Coefficient of Expansion) this refers to the rate at which glass expands and contracts when heated and cooled. Fusing compatible glass has been formulated, manufactured and tested for compatibility. All the glass in a single project must be of the same C.O.E. so they expand and contract at the same rate during firing. If they are not, stress cracks or breakage will result. 

A glass incompatibility break usually has more than one crack and it often happens a short time after the fused glass comes out of the kiln. The materials literally repel each other and so the broken pieces are angular and sharp. 

The fix: Pay close attention to the manufactures labels, store materials by C.O.E., clearly mark scrap and work with only one family of fusing compatible products at a time. Don’t trust that materials given to you are compatible unless they’re marked as such. 

Refusing the glass is not an option. But if you want to feel better, take a hammer to the project. Then use the pieces to make a mosaic or to line the bottom of a fish tank. 

The Dreaded Hole         

The dreaded hole in the project is caused by heating the glass to fast while firing on a very smooth surface like a primed ceramic self or Thin Fire fiber paper. As the glass is heated the perimeter of the project becomes soft first. It seals to the shelf like a suction cup.  The air trapped under the glass expands as it’s heated and pushes up on the glass forming a bubble. The glass bubble becomes thin, it pops and heals over at the full fuse temperature. 

You can fill the hole and refuse the glass, however a blemish will be visible in the new piece. If your design is organic the new detail may add interest. But if your pattern is pictorial, and unless the hole is perfectly located to represent the sun, not so much. 

The fix: add a segment to your firing schedule. In the heating phase of my firing schedule I have a hold at 1300 ° for 60 minutes. Holding at this temperature softens the glass in the entire project uniformly. This extra step is well worth the wait as it eliminates inconvenient eruptions and those nasty holes. 


Fortunately, the fusing spirits grant me many successes and very few mishaps. But every so often, no matter how hard I work, through no fault of my own, a single project or piece seems destined to failure. My general rule it to try to rework or salvage a failed project once and on special rare occasions twice. If at that point I’m not happy with my results I abandon the piece and start over from scratch. Hard earned experience has taught me, addition efforts are a waste of time and resources. My best advice when that happens is, let it go.

Here’s a quick example. I was building a huge 12 foot by 16 foot wall sculpture with 14 fused glass circles ranging in size from 12 inch to 48 inch across. All of the glass was special ordered from Uroboros. It came in a single crate. Five of the circles were made with the same color glass. All of the pieces were fired in the same kiln using the same firing program.

For some unknown reason, one of the five circles broke into two pieces after fusing. It cracked as neatly as an egg. No problem, I re-fired the two broken pieces onto a new, single piece of clear. I opened my big clamshell kiln, when it was at room temperature, the re-fired glass looked great. Happy with the result, I went back to my worktable a few feet away. 

It never happened before and hasn’t happened since. I was alone in the studio, just me and my glass. 

Out of nowhere, the lid on the clamshell came crashing down. I rushed over to the kiln and opened the lid. No big surprise, the fused glass circle was broken and in two neat pieces again. Dam isn’t the only word I used. My rapid fire expletives would’ve made a sailor blush. 

I got even by dumping the incontrollable pieces in the trash. Nope, I didn’t even trust them in a smaller project. Bye, bye! I made a totally new circle and it’s still intact ten years later.

With luck, this is the first time you’ve been introduced to these various ways that glass can misbehave. Hopefully, you’re now armed with the knowledge to avoid such disappointment. 

You can confidently explore more in-depth techniques and more advanced projects. 

But for added safekeeping, before closing the lid on my kiln I blow kisses to my darlings. You might try it.

Happy Fusing!

Vegas BABY!
Glass Craft and Bead Expo
March 29 – April 2, 2017
Las Vegas, Nevada

Join me in Vegas! It’s no gamble. You’ll have a great time!
There’s still room in these two classes!

Class#: SA-22
Class#: SU-01

Announcing New Upcoming Workshops and Webinars   

Advanced Glass Fusing Workshop
May 2-5, 2017
4-Days, Hands-on, 
Wesley Chapel, Florida

Push the boundaries art glass imposes. Explore innovative approaches to design and combine multiple advanced techniques to construct original art that reflects your own personal style. Enjoy: the one-on-one instruction, making large scale projects, the well-equipped classroom, and the intimate class size.

Inspiration! Knowledge! Confidence! Get the tools you need to create exceptional glass art here. You’ll love the concentrated, in-depth study and creative momentum you’ll gain while actively producing, nonstop for four consecutive days.

Creative Slumping Webinar
May 9, 2017

Meet me in West Palm Beach!
Glass Quest 2017
May 26, 27 & 28, 2017
West Palm Beach, Florida
A weekend of education, inspiration and engagement for glass enthusiasts of all types. Incredible networking opportunities, as well as overall engagement in the evolving world of art glass education & advocacy! Meet & partner with other glass artists as we push the boundaries of Glass as a Contemporary Art Form!

Breaking Through-Making Exhibition Quality Art
Hollander Glass Inc. – Texas
June 9, 10 & 11, 2017
3-day, Hands-on Workshop

Join veteran glass artist Lisa Vogt in this comprehensive workshop focused on making exhibition quality artwork and you’ll learn how to take your thriving glass talent and catapult it forward. Through lecture, demonstration and hands-on exercises, Lisa will show you how to accelerate your creative vision. Students will learn how to design thoughtful compositions, how to mix colors to create drama, how to get noticed with pattern, how to stimulate with texture, and how to combine abstract techniques for innovative works of fused glass art.

Upscale Fusing Webinar
July 25, 2017

Advanced Glass Fusing Workshop
September 26-29, 2017
4-Days, Hands-on, 
Wesley Chapel, Florida

You’ll love the concentrated, in-depth study and creative momentum you’ll gain while actively producing, nonstop for four consecutive days.
Push the boundaries art glass imposes. Explore innovative approaches to design and combine multiple advanced techniques to construct original art that reflects your own personal style. Enjoy: the one-on-one instruction, making large scale projects, the well-equipped classroom, and the intimate class size.


Friday, February 3, 2017

Firing Surfaces – A valuable guide for beginner to advanced fusers

Okay, you’re thinking I’ve run out of hot topics, if I’m writing about something as trivial as firing surfaces. But firing surfaces actually have a significant impact on the physical appearance and manufacturing cost of your finished fused glass artwork. In my experience, those two important factors make further study into the best practical uses of the many different options worthwhile. So, let’s get to it.

Ceramic Kiln Shelf: The advantages of using a ceramic kiln shelf are many. A well primed (kiln washed) ceramic self will give the backside of your fused glass a smooth, professional looking finish. Re-priming a ceramic shelf is fast and easy. Plus, doing so makes little dust or mess. (I prime my ceramic shelves with 3- 5 coats of primer before every use.) And, using a primed shelf is the least expensive, most cost effective way to fire glass.

One disadvantage to a using a ceramic shelf is the primer’s dry time. You can speed up the dry time by placing the wet shelf in the sun or by heating it in a vented kiln set to 500 degrees for 15 minutes. (Be sure to let the shelf cool completely before placing any glass on top.) Another drawback is weight. Ceramic shelves are heavy, so moving them in and out of the kiln can be awkward. Size is another thing to consider. Ceramic shelves tend to be cut considerably smaller than the kiln’s interior therefore reducing the number and size or projects you can fire at one time. By cutting a larger, tighter fitting kiln shelf from fiber board, you can increase the number and size of projects that will fit.  

Fiber Board as a Kiln Shelf: The fiber board we’re referring to here is a high refractory material purchased at your art glass supplier specifically to use inside a kiln. It’s available in a variety of sizes and thicknesses. The sheets I use are ½ inch thick, 24 inch wide and 36 inch long. This fiber board is primed with 3-5 coats of primer before every use. The pros: it’s lightweight and cuts easily to fit tightly inside any size kiln to maximize the firing space. It becomes smoother with every coat of primer and soon produces a finish that is close to the smoothness of ceramic.

The cons: the porous material retains moisture like a sponge, therefore its flimsy when wet with primer (so moving it when wet is not recommended) and it takes longer to dry than ceramic.

White glass, and some paint based labels like those on the backside of Grey Goose bottles, will stick to the board even if it’s well primed. Removing white based projects will pull a chunk out of the board. I fire these projects on fiber paper or primed ceramic to avoid damaging my fiber board shelves. 

Fiber board is soft. Dropping glass or other hard object on the shelf will put a hole in the smooth surface. The up side is damaged shelves can be cut down and used for shelves in smaller kilns. Or they can be cut into strips and used to dam cast glass projects. Nothing goes to waste.

Fusing on Fiber Paper: This is special paper purchased at your art glass supplier for kiln use. It’s a convenient material designed to act as a release between fused glass and the kiln shelf. Fiber paper comes in a variety of thicknesses.

Thin Fire looks, feels and cuts like regular paper. It’s identifiable by the name printed on the backside. This is a convenience product that delivers a nice smooth finish. It’s ideal when you want to quickly swap projects in and out of your kiln without having to prime shelves. The disadvantage is cost and clean up. Thin fire costs several dollars a sheet. It’s a onetime use product that turns to dust after fusing. Clean up involves vacuuming the left over material out of your kiln.

Thin fiber paper is slightly thicker than thin fire. It has a smooth side and a textured side. Even the smooth side leaves a slight pattern behind on the backside of projects. If handled carefully, you can get more than one use out of the paper. I like to use it to emboss patterns in the bottom of my artwork. I cut shapes out of the paper with scrapbooking punches. The project it assembled in the kiln on top of the cut outs and fired. It’s a fun, easy way to add detail to your work. The disadvantage to using this material to cover a kiln shelf is the texture it leaves behind and the cost it adds to the fabrication. Clean up involves vacuuming the spent material out of your kiln.  

1/8 inch Thick Fiber Paper is stiff enough and durable enough to contain thick glass during the fusing process. I cut it into strips and use it to hold cast glass projects in place. The nice thing is that you can design your own custom shapes and sizes without being limited to readymade casting molds. It can also be used to make deep, ornate embossing patterns, in the backside of your artwork. If handled carefully, it’s possible to get more than one use out of this paper. Due to the added cost of this thicker material, it would be used to cover a shelf only for specialized purposes. Another drawback to this particular paper is the visible texture on both sides. Like it or not, this paper leaves a noticeable impression in finished glass projects.               

Fiber Blanket: This material is very versatile. It comes in several thicknesses that have multiple uses. I use it to cover the kiln shelf when I want to create a project with rustic texture and a wavy free form edge. It’s also flexible enough to drape over slumping molds to achieve organic shaped pieces of art. It can be primed to give your art a shinier finish or left raw for a frosted finish. Stored carefully, his material is very resilient and can be used in any number of ways over and over again. Fiber blanket costs more than the other fiber materials, but it’s worth having a sheet in your studio due to its durability and for its experimental value. 

When deciding on a firing surface, I consider what I what to accomplish with a particular project and then select the best surface to achieve that outcome. I’d recommend having all of these materials on hand. Then, when a unique project presents itself, you’ll have the flexibility to fire it on the surface best suited to create your desired effect.  

Keep it hot!

There’s still time to register! One seat left!
Advanced Glass Fusing Workshop
February 21 -24, 2017.
Wesley Chapel, Florida

Inspiration! Knowledge! Confidence! Get the tools you need to create exceptional glass art here.

You will love the concentrated, in-depth study and creative momentum you’ll gain while actively producing, nonstop for four consecutive days.

Push the boundaries art glass imposes. Explore innovative approaches to design and combine multiple advanced techniques to construct original art that reflects your own personal style. Enjoy: the one-on-one instruction, making large scale projects, the well-equipped classroom, and the intimate class size.