Frequently Asked Questions and Troubleshooting


We get questions and our Fuse Whisperer offers answers to some of the mystifying challenges that glass fuser’s encounter. If you have a fusing question email it to: fusewhisperer@joyoffusing.com and we try to answer it for you. Then we’ll post it here for all to see and absorb. Remember to include all the details you can think of that might help ‘The Whisperer’ determine what went down and please include some relevant images as well because as you know “a picture is worth a thousand words!” We look forward to hearing from you.


Are the firing schedules in Joy of Fusing for COE 90 or COE 96?

Dear Fuse Whisperer: I just bought your book Joy of Fusing and have read it twice and can’t wait to try some of the projects. I have one question. The firing schedules that are given for each project, are they for COE 90 or COE 96? I noticed the anneal soak temperature was 950°F (510°C) which I thought was for COE 96. Do I need to make an adjustment to use COE 90? Thanks for the great book and the help. -Soaking in the Heat in Chico, California.




Dear Soaking:

Good question and one that I have given a lot of study. As best I can tell the anneal soak temperature is not determined so much by the COE but rather by the recommendation of the glass manufacturer. For instance Bullseye Glass (COE 90) recently changed their recommended anneal soak temperature to 900°F (482°C) – for many years Bullseye recommended a soak temperature of 960°F (515°C). Spectrum Glass (COE 96) recommends an anneal soak temperature of 950°F (510°C). Uroboros Glass (makes both COE 90 and COE 96) and they recommend an anneal soak temperature of 960°F (515°C) for all their glass. Wissmach Glass makes a fusing glass (COE 90) and the recommended anneal soak temperature is 960°F (515°C). It seems that most are in the 950°F (510°C) range (except for Bullseye’s recent change).

The fundamental purpose of an anneal soak is to stabilize and balance the temperature of the glass from the surface to it’s core. That is why the thicker the glass the longer it must soak to make certain the entire piece is the same temperature – somewhere between 900°F and 960°F (482°C to 515°C). Then the glass must cool down slowly from the anneal soak temperature to 700°F (371°C). The idea behind the anneal scheme that we use in our book is to stabilize the glass at 950°F (510°C) then restrain the cool down to pass through the lower anneal temperatures at a slow – almost soak-like speed.

One other important reality is the fact that the temperature readout from one kiln to the next varies by plus or minus 5°F to 50°F, so we had to take that into consideration as well.

The objective of our book Joy of Fusing was to make fusing as simple, reliable and JOY-ful as possible. We consciously tried to minimize the variables in the fusing process and that is why we settled on an anneal soak temperature of 950°F (510°C) for all glass types with a slow descent, anneal cool ramp speed of 125°F (67°C) per hour down to 700°F (371°C). We have used this formula for many years on hundreds of pieces that were fabricated using each of the manufacturer’s glass and it has worked beautifully.

Now you have to make your own decision. If you are more comfortable making an adjustment to the anneal soak temperature to follow the glass manufacturer’s recommendations then you most certainly should change your schedule to match the glass you use for each and every project.

However if you are creating small to medium sized pieces, similar to the projects we featured in the book Joy of Fusing, then the annealing soak temperature and ramp speeds they we have listed should work just fine for most glass made for fusing.

Hope this helps – The Fuse Whisperer

I Fired to the Recommended Firing Schedule but My Piece Doesn’t Look Like the One in the Book – Why?

Dear Fuse Whisperer: I have your book Joy of Fusing and really enjoy it – great ideas, great illustrations and great instructions. I especially love the “Fusing Level Sample Tiles” idea and I am in the process of creating them now.

Of course I couldn’t wait until my tiles were done before trying your Glass Fritage technique, so I made a simple piece and fired it to the Fritage Development Schedule in the book but it came out of the kiln pretty much like it went in – only minor melting of the glass. I didn’t know if I should add temperature or add soak time so I tried increasing the Final Target Temperature by 10°F (6°C) and it came out a bit more melted, but still not right. So then I left it at that higher temperature and added 5 minutes to the soak (total 15 minute soak). Results were better but still not right!!! BTW: I am using a Skutt Hot Shot Pro kiln.

I would appreciate any help & advice you can give to me – I’m Still Not Right in Wichita

Glass Fritage from page 84 in the book Joy of Fusing.




Dear Not Right:

I’m so pleased that you’re enjoying our book and that you’re getting some good ideas and inspirations from it. I’m also very pleased to hear that you’re making a Fusing Level tile set. This is one of the most valuable things you can do for your studio and you will refer to it time and time again, I promise.

In fact, had you finished your Fusing Level tile set you would probably already know the answer to your question. Let me walk you through the process. First of all adding soak time is not the way to solve this problem. Adding soak time to the Final Target Temperature can solve some issues, in particular if an outcome is very close (but not quite) what you’re looking for, adding an extra 10 to 20 minutes is a good way to fine tune a fusing level. However in this case you really need to find what I call the ‘middle range’ temperature of your kiln – what we’re looking for is the schedule that will produce an FS3 – Texture Fuse outcome in YOUR kiln (see image at left and on page 27 in JOF book).

And here’s the way to do that. Use the Fusing Level tile pattern (download the full-size pattern here) to create a simple tile. You don’t have to make your tile quite that fancy, just make sure it is 2 layers thick and has a few design pieces arranged on top. Now place that tile in your kiln and program the controller to fire the FS3 – Texture Fuse schedule (at left and on page 27 in JOF book) with a Final Target Temperature of 1330°F (720°C) and a 10 minute soak. Close the lid and wait until your kiln has come back to room temperature (12 to 15 hours). When you open the lid I suspect you’re going to see a tile that looks very much like the FS2 Dimensional Tack level or it may be closer to the FS1 Elevated Tack level or it could be somewhere in between these levels. Your job is to determine which level your tile is closest to (compare your tile to the Fusing Level tile photos in the book – or at left). If you feel your tile reached a perfect FS2 Dimensional Tack level then we can use that information to calculate that your kiln needs to fire 40°F (20°C) hotter than the schedules in the book because, 40°F (20°C) is the difference between the FS2 and FS3 Final Target Temperature. Now all you have to do is add 40°F (20°C) to the Final Target Temperature to any schedule in the book to make the adjustment for your kiln. You don’t have to adjust any of the other temperatures in the schedules or any of the soak times – adjust only the Final Target Temperature.

By the way if you determined that your tile was closer to an FS1 level then you may need to add 60°F (33°C) as the adjustment for your kiln (the difference between FS1 and FS3 is 85°F- 45°C) or if it were half way between an FS2 and FS3 level then you may only need to add 20°F (11°C). Do you see how I’m getting these numbers?

So back to your Fritage schedule question. Let’s assume that your kiln needs an additional 40°F (20°C) – that would mean the Final Target Temperature for a Fritage firing in your kiln would be 1400°F (760°C) – that’s 1360°F (740°C) plus the 40°F(20°C) difference. The rest of the schedule for a Fritage would be the same as it is in the book. That’s all it takes to make the adjustment to the schedules we have listed so they will work in your kiln. I hope this explanation meets your approval. Once you get your kiln numbers figured out you can sit back and have fun without having to worry about “How Fused Will It Be”

“Hope this helps – The Fuse Whisperer

How Are You Able to Create a Bowl With Just One Layer of Glass?

Dear Fuse Whisperer: I noticed that the Graffiti Bowl design (that is in the Starfire Mold booklet) was created with only a single layer of glass on the base with the design components added on top. I have always thought that since glass wants to be 1/4″ – 6 mm thick (due to surface tension), that it was necessary to always use two full layers of glass (plus the design layer) to ensure that your piece doesn’t shrink inward when it is fuse fired. Please explain how are you able to create a bowl with just one layer of glass? – A Question of Thin in Oregon




Dear Thin in Oregon:

You pose an interesting question. It’s true that when glass is heated to melt temperature and left on its own it does want to be 1/4″ – 6 mm thick. However that does not mean that it cannot be influenced to be any other thickness. After all most of the sheet glass we use is 1/8″ – 3 mm thick and that is accomplished by squeezing the glass through a series of rollers to compress it. Conversely if glass is contained using a casting dam, it can be cast to any thickness (over 1/4″ – 6 mm) that we choose to make it.

That being said, you are correct that if we placed a 12″ – 30.5 cm diameter single layer of glass in a kiln and fired it to full fuse temperature it will definitely contract and this will be most evident around the edge. But it would take a very long soak at full fuse temperature before that glass was able to shrink enough to become 1/4″ – 6 mm thick. I’m sure it would eventually get there but I can’t even begin to estimate how many hours that would take.

So to answer your question about creating a piece with just one layer of glass. I create my flat design starting with a single layer on the base, then I add my design pieces on top of that base layer. If I’m creating a design for a vessel using this method I usually add some kind of rim wrap such as a cut glass border or a series of squares (see GeoStraws Bowl left) or some other kind of edge design. Then I prefer my work to have some texture, so I like to fuse to a Texture Tack at 1330°F -722°C or a Contour Fuse at 1370°F – 743°C (with a 10 min. soak). Fusing at these temperatures rounds off the outer perimeter very nicely (that’s the inward shrinking part) but it does not significantly alter the size of the blank. A 12″ – 30.5 cm diameter may shrink to 11 7/8″ – 30.2 cm but I can compensate for that by cutting my blank slightly larger if I need it to be closer 12″ – 30.5 cm (which I usually don’t). Then I place that flat blank on a mold (I used the Starfire Mold for this bowl) to give it shape, just as I would if the flat blank was a 2 layer fabrication.

Hope this helps – The Fuse Whisperer

Help – I Can’t Get My Cast Glass Foot Out of the C105 Foot Mold

Dear Fuse Whisperer: I fired my new C105 Foot casting Mold for the first time last night and when I open the kiln this morning it looked great except the glass was really, really stuck in the mold. I tried everything to get it out, I slammed the mold face down on my plywood bench several times, then I tried using a screwdriver to pry it out. The mold finally broke into several pieces, along with the glass foot. The glass looks like it is actually welded to the ceramic. Here is exactly what I did: I sprayed the mold with 3 coats of Slide Hi-Temp 1800™ mold release and let it dry for 1/2 hour. Then I created some shards from scrap pieces of System 96 clear glass and made sure that the shards were no greater than 3/4″ (2 cm). I cleaned and weighed out 90 grams of shards and put that into the mold cup. I used the Scrap casting Schedule from the booklet that came with the mold except I raised the target intention temperature to 1450F (788°C) because I know my kiln runs a bit cooler than most schedules. As I said, when I open the kiln it looked great except the glass was really in the mold. I have included a few photos of the whole mess after I broke it. Can you tell me went wrong? – Stuck & Broken in Paso Robles




Dear Stuck & Broken:

Thanks for including the photo, Ii’s easier for me to deduce a problem when I can actually see the end result (see image at left). However I didn’t need the photo in this case to know exactly what the problem is.

The only Boron Nitride separator that we use and recommend is ZYP™ Boron Nitride spray (formerly MR-97) – especially for casting molds like the C105 Foot Mold. The Slide Hi-Temp 1800™ mold release product that you used has a relatively low concentration of Boron Nitride – Slide’s own literature says their product contains from 1% to 5% by weight. By comparison ZYP™ contains 15% to 20% Boron Nitride (by weight). New molds require 2 coats ZYP™ (manufacturer’s recommendation) with a 20-minute drying time. For subsequent firings simply brush the surface with a soft brush (we use our bench brush) to remove the loose powder then one spray coat is all it takes.

Since you used a lower concentration brand of Boron Nitride spray (Slide Hi-Temp is only one of several available) you would need to apply anywhere from 8 to 20 coats to a new mold to get a coverage similar to ZYP™ and the result still may not be satisfactory.

Trust me when I tell you that we have tested most of the separator products available on the market today and we have settled on ZYP™ Boron Nitride spray because it has provided consistent success – especially for casting molds like the C105 Foot Mold.

Hope this helps – The Fuse Whisperer

I can’t get my draped bowl off the M35 Starfire mold.

Dear Fuse Whisperer: I draped my bowl over the M35 Starfire Drape Mold yesterday including a stemmed foot and I was so excited to open the kiln this morning. The bowl looked great but when I tried to take it off the mold it wouldn’t come off. The glass is not stuck to the mold, it’s loose and I can move it on the mold but the glass on the rim of the bowl has closed in around the bottom of the mold and has captured the mold. I don’t want to lose my beautiful bowl or break the mold, what can I do? – Captured in Des Moines

Dear Captured: I have a solution for you but I would like a little more information about your project before I make my pronouncement. Stuff like, the diameter of the flat blank, the base glass color and type, how many base layers, what type of decoration, did you add a perimeter border, what was your target intention temperature and hold time for the drape schedule? Also if you can email a photo of the bowl as it is now that would be a big help.

Reply from Captured: OK here a couple of photos of the bowl stuck on the mold. In one of them I’m pointing at an area where the glass has pinched in around the mold. Here is what I did: I cut a 12 1/2″ (32 cm) diameter disk from System 96 clear and only used 1 layer because I wanted to keep the bowl as light as possible. Then I added a 4 1/2″ (11.5 cm) black glass disk to the center and decorated the rest of the disk from the center out with various colors and grit sizes of frit and some stringers. I did not put a border or decoration around the perimeter so the edge is only a single layer of glass. I modified the drape schedule that came with the mold by adding 20°F (11°C) to the target intention temperature to make it 1250°F (677°C) for 10 minute hold because that is what I have used successfully for slump firings in the past. So what’s your solution? I can hardly wait!




Dear Captured: To avoid this predicament in the future let’s look a few things that I suspect may have caused it in the first place.

1. A diameter of 12 1/2″ (32 cm) for the base disk is too large for this mold. We do not recommend anything larger than 12″ (30.5 cm) diameter – so that’s important.

2. Even with a 12″ (30.5 cm) diameter disk, a capture like this can still happen particularly with a single layer blank that does not have a rim border (that would give the border a little more substance and rigidity).

3. If the target intention temperature of the drape is too hot the glass will over-soften allowing the edge to curl under the lip of the mold. Even though you used a target intention temperature that worked well for slump firing in the past, I suspect it was too hot for this drape particularly with a single layer edge. You might need to drop your target temperature back 15° to 20° to compensate.

OK you’ve waited long enough – here’s the fix. You can save the bowl and the mold by firing it again. You said you added a foot to the bottom so leave the fiber rings in place and put the bowl (with mold inside of course) back into the kiln standing right side up on the foot. Note: If you did not add a foot you would put it into the kiln standing on the bowl base. Now set your kiln controller to use the standard drape schedule but reduce the target intention temperature to 1000°F (538°C), set a 30 minute soak then set your controller alarm to go off at 1000°F (538°C). If you don’t know how to set the alarm on your kiln controller, you’ll have to read the owners manual again (you have read it at least once, right?). Now when the alarm goes off, put on your kiln gloves and safety glasses, open the lid and take a look at the bowl rim. It probably will not have moved away from the mold just yet – but it will soon, so close the lid and be patient (and don’t leave the kiln room). Allow 10 minutes soak and look again. If the glass has moved a little (but not enough) simply close the lid and let it soak a little longer. If the glass hasn’t moved at all you can try adding 10° to 20° to the target temp (again, this is in the controller manual so read and figure out how to do it ahead of time). Then wait until the new temperature is reached and take another look. This is very much a wait and watch process that you cannot hurry because if the glass gets even a little too hot it will collapse and fall down around the mold – so low and slow is the only way to go. By the way, even if this recovery effort works perfectly the bowl will have some rim marks from the mold and possibly other edge blemishes, but the bowl and the mold will be saved and you will have learned a lot about your kiln and how glass reacts at lower temperatures. Good Luck and be sure to send me pictures.

Reply from Captured: I did it and it worked – attached are some photos of the bowl in the kiln before and after firing and one of the finished bowl. You’re right there are some marks and odd angles around the rim but that just adds to the mystery of my piece that I call “Houston – I Found a Black Hole”. Just so you know, I had to go to 1020°F (549°F) in my kiln before the glass started to move then it only took a 5 minute soak to back off the mold before I hit the ‘Skip Step’ on my controller to send it into the ‘drop to anneal’ segment. Thanks for helping me save this bowl. – Released (and relieved) in Des Moines

Dear Released: You’re welcome and I love the bowl, keep up the great work!

– The Fuse Whisperer