Stained glass firing schedules
Firing shouldn’t be a problem. ‘Shouldn’t be.’ Yes, I know there are times when, no matter how experienced we are, everyone gets anxious about it. I’m just the same.
But really it’s far easier and more predictable to fire glass paint than ceramic glazes for example. There’s also much less to think about than if you’re fusing. What I’m saying is, glass painters are actually very lucky here: it’s important to keep things in perspective. So here are 12 quick points I always run through before settling on a particular stained glass firing schedule. These points let me get a good night’s sleep (because I mostly fire overnight, you see).
First thing is …
1. The manufacturer’s instructions
Different makes of glass paint – paint you use for tracing and shading etc. – will need different top temperatures to fuse with glass.
And, around that recommended top temperature, there is a range of acceptable results which you must choose from, depending on whether you want your fired glass to look dry or shiny for example. Also whether you want your trace lines flat with the glass (more heat/longer soak), or slightly raised (less heat/shorter soak). This particularly matters when you’re doing restoration.
Likewise with enamel and silver stain: different brands, different chemical compositions, different instructions which you can’t ignore.
The manufacturer’s instructions are a valuable place from which to start. So if you have a batch of nameless ‘paint’, you’ll just have to do some tests and discover things for yourself.
2. Your kiln
Even when you know what the manufacturer recommends, you still have to see how it works for you.
And even when you know our firing schedules, you still have to test them for yourself.
The reason is, every kiln is different.
- Different cool spots
- Different heat diffusion
- Different heat retention
I don’t want to make a big thing about any of this because like I said before, the glass painter’s life is broadly very simple.
So here I think it’s best you don’t get over-scientific.
Maybe I get the result I want at 660 Celsius / 1220 Fahrenheit. And maybe you get the same result at 665 Celsius / 1230 Fahrenheit.
So, once you know your kiln, you just add on or subtract a certain amount from another person’s recipe.
Yes, exactly as you would with your own kitchen oven.
It doesn’t take long to get to know your kiln. When I got my first one (which still works beautifully, 13 years on), I took lots of notes.
After three months, I didn’t need to.
Nowadays, I just take a few notes when I’m running tests or experimenting with a new medium.
3. Shelves – or not
If your kiln has shelves, it’s likely the glass on the bottom shelf will fire differently to the glass on the top shelf.
The main reason is heat rises, and then cools.
Myself, I don’t like shelves.
Both our kilns have just one surface on which we place our trays. The heat is pumped down from above (yes, heat source is another factor to consider) from coils (electric: not gas: another factor) which are evenly distributed within the lid. This means (apart from the two cool spots: I know where they are) all the glass gets the same treatment, which is how I like it. Nothing for me to think about here.
We use electric kilns here. They work fine for us. I’m sure there are areas where gas vs. electricity makes a big difference (other than speed), but it isn’t something I’m qualified to talk about.
Whatever you use, just be sure you have full control of the schedule so that e.g. you can dry off the moisture or burn off/vent any unwanted fumes.
If someone else is firing your glass, don’t put up with what they want.
Maybe they just want a quiet life.
With all the good will in the world, your problems aren’t the same as theirs.
Whereas they just probably want their kiln back, you want to take control and run some tests – yes, even though these tests will cost you extra time and money.
Be sure to get it right. Even if you make a nuisance of yourself and also end up paying more.
Which brings me to the other points I want to mention now. I mean, important factors like:
8 more factors
All sorts of things:
- The media you’ve used, because this can sometimes make a difference: water, and/or different kinds of oil, propylene glycol, vinegar, and so on
- The specific techniques you’ve used, especially how much flooding / blocking in / silhouetting, because you don’t want your paint to blister in the heat
- Painting on the front, or on the back as well, because the back will take longer to get hotter than the front (remember that the gadget which measures your temperature is not responding to how hot your kiln shelf is)
- The type of glass, which especially matters for silver stain, but it also matters generally because some glass is harder than others and so it softens at a higher temperature
- The size of your pieces. This particularly affects the speed you choose to cool down. Larger pieces demand a slower rate than smaller ones
- Also their thickness, again because they’ll take longer to heat up and will be slower to cool down evenly
- How full / empty your kiln is: when I want to burn off moisture (e.g. with flooding), I soak longer at 100 Celsius / 220 Fahrenheit on a full kiln than I do if I am firing just three pieces
And also – this is very important: I’ve seen it make a big difference, not just with silver stain, but also with firing ‘ordinary’ tracing paint:
- What surface are you firing on? For example, whiting, fiber paper or fiber board, or kiln spray? Myself I don’t like anything which gives off a smell. I like things to be as simple and natural as possible …
That’s why I love whiting – powdered chalk.
Seen our video of how to load a tray with whiting? Watch the video here.
You OK with all this?
Right, so how scientific and methodical should you be?
Fact is, you’re the best judge of that.
Me, overall I’m cautious.
But I am not excessively precise.
I think one quickly gets to the point where ‘precision’ is misleading or spurious.
I mean, it’s easy to get too precise: and too precise is actually superstitious (unscientific) here.
Good “rules of thumb”: that’s what we all need.
And these are things we develop best for ourselves, knowing the specifics of our own situation.
But me, well, first, I like to run tests so that I can then get on and paint with as much confidence as possible in this world where (sometimes, sometimes) things go wrong.
How many tests?
As many as I need to paint peacefully: peace of mind and freedom to concentrate on the task in hand is always what I’m after.
Second, I like to fire as slowly as possible, mostly overnight.
After all, I’ve painted layer upon layer in just this one firing.
Which means I’ve finished the piece in a fraction of the “elapsed” time it would take me if I had to fire each layer separately.
Therefore I can easily wait until tomorrow to get it out.
Yes, cautious: that’s me.
I’d love to know.
One last thought …
Sometimes it’s right to blame the kiln. Many times – especially with flooding, enameling and silver staining – I’ve seen poor firing wreck good work.
But I haven’t seen the opposite: good firing can’t mend bad technique. Harsh truth is, if your technique is wrong, don’t blame the firing schedule.
And if it’s good technique you want, stick with me and David. If you take our advice and also put in the practice, I promise you’ll see results.
But you must put in the practice.
If evolution or God had meant us to paint stained glass, we’d have tiny hairs on the tips of our fingers.
It / He / She didn’t.
Therefore, we must practice.
That includes me. And also David.
Let me know.