How to Fire Stained Glass – 12 Points You Need to Know

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.

For example:

  • 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.

4. Power

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.

Remember:

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.

OK?

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?

Great!

Method

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.

Stained glass firing schedules - this will work: we know because we've done our tests

Stained glass firing schedules – this stain will fire beautifully: we know because we’ve done our tests

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.

Stephen Byrne

Stephen Byrne

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.

And you?

I’d love to know.

Best,

Stephen Byrne

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.

We don’t.

It / He / She didn’t.

Therefore, we must practice.

That includes me. And also David.

Questions?

Let me know.

Comments

  1. Peter Murdoch says

    Helpful overview, thanks. My question is, have you tested firing silver stain on fiber paper vs. firing it on whiting?

    Best,
    Peter

    • says

      Yes. And in our experience, fiber paper was a less stable and less predictable ‘environment’ on which to fire our stain than whiting.

      For instance, even if one lot of fiber paper works fine for stain, I can do nothing to be sure the next lot will work the same way.

      The reason is, I have no control over how it’s made.

      Whiting, on the other hand, is simple.

      See this window here. The owners called us in because one of the central rectangles was missing: they wanted us to make a copy.

      The sample pieces all worked fine: they were small enough for us to fire on our trays and whiting.

      This lured us into a false sense of security: we then made a full-size piece and, because it was too big for our trays, we fired it on fiber paper.

      It didn’t work.

      Now, thinking methodically, we couldn’t discount the possibility that the different sizes were to ‘blame’.

      On the other hand, the simplest variable to eliminate was … the fiber paper.

      So we made another full-sized piece and next time sprinkled whiting as evenly as possible across the boards which form the bottom of our kiln, then pressed it down.

      The next firing worked fine, as you can see.

    • says

      Hi Hassan,

      Thanks for your message. Glad it’s useful. Remember, whenever you have questions, just write and say.

      Best,
      Stephen

      P.S. When firing propylene glycol (which is wonderful) like you see in The Master & the Beast, we just slowed down the rise to the first soak at 100 Celsius / 220 Fahrenheit and kept it there for 15 minutes. Then up and down in the usual way.

  2. Virginia Heller says

    I just had two mild steel frames made and am putting fiberboard in the frames then topping this off with about 1/8th to 1/2 inch of whiting (which was not easy to find here in the U.S.!) I am very excited but I wanted to make sure before I use this in the kiln: the fiberboard manufacturer says I should coat it with hardener before I use it. Do I need to do this if I am just using it to cover the bottom area in my frame? – The fiberboard will never come in contact with the glass.

    Then the bigger question is: can I put this mild steel frame on the floor of my kiln? Is the metal going to heat up differently than the fiberboard and then crack a brink in the kiln? Do I need to place the whole “system”/tray on a kiln shelf off the floor of the kiln? I am ready to go but something about heating metal in the kiln makes me nervous – probably because of the advent of microwaves and the no-no’s about metal in them.

    • says

      A quick reply for now because you’ve asked urgent questions.

      First, I am certain we didn’t harden our fiber board before using it in our kiln trays. But it is likely we did fire off its fumes before we first covered it in whiting: this is where you take it through a slow firing cycle and burn off various chemicals. This gives off lots of very ugly smells, so be prepared and open up your doors and windows. It’s just the once this happens. Once is quite enough though.

      Second, yes, you do place your mild steel tray on top of a kiln batt (or shelf). The batt is usually made from a general purpose material like mullite or cordierite. It’s the same as potters use, so a company which sells accessories to potters will surely have what you want. The batt sits directly on the bottom of the kiln; the tray, filled with whiting, sits on the batt. The batt does not require any special preparation each time you fire.

      Third, just to emphasize, our trays are made from 4 lengths of mild steel “L-section”. This means there is a fairly large rectangular hole in the middle: it’s this hole which the fiber board “plugs”. I believe it’s also the fact of the hole which means you don’t get warping.

      I hope this helps. Ask more questions as they occur to you.

      Best,
      Stephen

  3. Virginia Heller says

    Thank you for your help. Well, now I am ready to try out the whiting. You are both so generous with your time and knowledge. I am very grateful you are around. I will open the doors and get the stinch over with. I have indeed heard that it really stinks to fire (the fiber board).

    • says

      Virginia,

      You may not need to use an alumina hardener on your fiber board, but if you don’t, the board is quite soft and rapidly degrades. The addition of the hardener will make the board very durable. Follow the manufacturer’s instructions. It becomes almost as hard as a kiln shelf, but much lighter and will not thermal shock.

      Try ceramic supply companies for whiting (calcium carbonate). It is easily available. I get mine from a local paint company that compounds their own line of paints. This is in Iowa.

      • says

        I have always used powdered plaster of paris, (gypsum?) as I was taught at college in the ’60′s. I don’t know if this is what you call whiting in the States, but I don’t think so. Finer than Whiting and usually easier to get hold of. And yes, as the last guy said, if you don’t harden your shelf, it will warp or disintegrate quite quickly, as the original hardener they use burns out.

  4. Rhyce says

    I find my 240v kiln is quite inconsistent, and its major inconsistencies occur when it is a hot summer day so I would definitely advise keeping a very detailed log for anyone with a new unfamiliar kiln. For the first 2 dozen firings I logged the ramping temps every ten minutes so I have a good indication of fluctuations and what sort of time frames are needed for different types of paint finishes on different glasses. I find some glass, red especially, needs special attention as it seems softer than most other colours – that’s my experience anyway. There’s nothing more fear-inducing than sticking several hours of painstaking work in the kiln hoping for the best!

    Now, do you have any suggestions about reducing water-based matt burn-off: they seem to lighten significantly after a smooth finish firing? I find I have to keep before and after matt samples to ensure I am going to have a finished piece with good contrast, not a light “muddy shaded piece of glass.

    I love the words of wisdom by the way: thanks!

    Rhyce

  5. says

    Hi Rhyce,

    Thanks for joining in: yes, a detailed log is definitely the way to go either with a new kiln or with a new project which calls for new / modified techniques.

    You ask about reducing water-based burn-off.

    OK, this is when the fired painted glass you remove from your kiln looks lighter than the unfired painted glass you put into your kiln.

    It’s a fact: about 10% or 15% of the ‘darkness’ of your lines and shadows is lost in firing …

    But not if you ‘seal’ your water-based painting with a wash of oil-based paint or glycol-based paint.

    So, if burn-off is giving you problems, I’d definitely suggest you paint some simple pieces, and then experiment with oil or glycol. It makes a huge difference.

    People who get our newsletter also got this great video right here which I’ll make public just to show people who don’t get the newsletter what they are missing: just watch this glass painting video of using oil on top of water-based paint and you’ll see what I mean. OK I admit the video is about shading (not preventing burn-off as such). But that’s an added benefit: you can shade more easily and also reduce burn-off when you seal your water-based glass paint with something that is not water.

    Second, this new glass painting DVD shows you two full-length demonstrations of oil and also glycol.

    Best,
    Stephen

  6. says

    estimados DAVID-Stephen
    Excelentes tus comentarios mira yo estoy usando como desmoldante papel ceramico bullseye y realmente es espetacular mis resultados solo transmito mi esperiencia
    gracias a ustedes siempre informando
    un abrazo de argentina
    rubèn

  7. carol says

    I flatten or slump bottles. Is there ANY glass paint that I can use to paint lettering such as initials and quotes on the glass bottles that I can kiln-fire at the same time as when I slump the bottle that is bright and permanent.

    Thank you!

    • says

      I’m sure there is though I have not done the tests myself. In your position, I would buy a small quantity of Reusche tracing black (DE401). Then do some experiments until you get the result you want.

      Please note: if you slump and fire the glass paint in single firing, whatever you paint will certainly be distorted at the same time as the bottle flattens. This may be fine; or it may not (your lettering will definitely change its shape). If distortion is not acceptable, you’ll need two firings: one to slump and one to fire the paint.

    • oriel says

      If you find a potters’ supplier, you can get gold, bronze, silver or even platinum lustre. It is dark brown before firing but you can paint it on with a fine brush, cleaned with spirit. This fires at between 670 – 800 ish and leaves a permanent gold/ silver/ bronze design. Ideal for lettering, if you have a steady hand, and it fires at the right temperature for slumping.

  8. Bruce Medema says

    Happened upon your comments here … It’s great to hear open discussion about glass painting!

    I am also a glass painter and welcome any banter about the medium. (It’s a love /hate relationship at times!)

    Thanks!
    Bruce

    • David Williams says

      Hello Bruce,

      I’m glad you found us, and I hope you’ll find many useful discussions here.

      Best,
      David

  9. Celeste says

    Hi!

    I really like your website!

    Two questions please …

    1 At what temperature does paint stick to glass? (Have to paint two layers and just want first layer to stick so we can save time as second firing will gloss both.)

    2 If we don’t have gum Arabic, what would you suggest to save on firings? (We tried mixing the paint with vinegar and it didn’t stick.)

    Thanx a mil!

    • says

      The temperature at which glass paint sticks to glass – what you’re after is called a ‘tack firing’ – depends on the glass paint, your glass, your media (e.g. water, oil, glycol etc.) and your kiln (since ’1020′ in one kiln is not necessarily the same as ’1020′ in another kiln). So you will need to do some tests to establish the minimum temperature you require. Since you make it clear you wish to save time, you might wish to re-consider your plan and choose instead to fire each layer separately and properly.

      Vinegar can certainly work, so you will just need to practice till you get the proportions right, and also the technique. Another option is to get some gum Arabic.

      Overall, it seems you might do better to pull back and slow down and test and practice till you get the kind of results you will be proud of if your glass were fortunate enough to survive a couple of hundred years.

Leave a Reply

Your email address will not be published. Required fields are marked *

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <strike> <strong>