Fire-Polishing

What is it?

Ivo de Croock wrote to us from Antwerp, Belgium, and asked what we meant by the term “fire-polishing”.

In the first place, we don’t etch with hydrofluoric acid at our studio. (When we must use acid, a colleague lets us use their studio and their equipment.)

But we sometimes etch by sand-blasting.

Now the sand abrades the surface of the glass and leaves it rough where it has blasted through the layer of flashed colour i.e. where the glass is not protected by your stencil.

It’s a good idea to use as fine a grain of sand as possible. This is especially worth remembering if you’re using another person’s sandblaster; the sand they have might be so coarse it would blast your glass to bits, which you do not want.

It’s now that we “fire-polish” the sand-blasted glass.

  1. We put it in the kiln and fire the glass to about 710 Celsius / 1310 Fahrenheit.
  2. We soak it there for about five minutes before descending and annealing.

This has two effects.

It smooths the sand-blasted glass.

It also softens the line where the sand-blasted glass meets the glass which has not been sand-blasted.

All in all, the glass seems to us to appear more like a liquid than it did before.

After the fire-polishing, we paint and stain it as we normally would. Consider this small panel here: we’ve sand-blasted flashed pink-on-white, fire-polished it, then traced and fired, and finally stained and fired:

Fire-polished stained glass panel

Fire-polished stained glass panel

You will need to test things for yourself

When you use sand-blasting and fire-polishing instead of hydrofluoric acid, you will need to run some tests:

  1. How thick must your stencil be?
  2. How fine / coarse must your sand be?
  3. What is the top temperature of your own particular firing schedule?
  4. How long do you need to soak there (if at all) to achieve the effect you want?

I can’t give you answers to these questions: the answers depend on your sand, the strength of your sand-blaster, the thickness of your flash, and the hardness/softness of your glass, plus of course its size, and the particular kiln you’re using.

 

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11 thoughts on “Fire-Polishing

  1. Hey there!

    I was wondering why my paint has a matte finish after it’s done. I fire it around 1165 Fahrenheit and let it soak for 15 minutes.

    Should I fire it at 1200 Fahrenheit for abour 20 minutes?

    Thank you so much!
    Cheryl

  2. Hi Cheryl,

    We fire our Reusche tracing and shading paint (DE401) at 1250 Fahrenheit (675 Celcius) and might also soak it for 3 minutes. That gives us a smooth and shiny finish.

    If this doesn’t work for you, maybe you’re using a different brand and make of glass paint; or maybe your kiln is giving a strange reading …

    You can download our firing schedules from the stained glass painting guides page.

    I hope this helps.

    All the best,
    Stephen

    P.S Join the stained glass painting newsletter and get free tips plus online video demonstrations. Do it right here. Right now!

  3. Stephen,

    I fire at 1250 degrees and still get a matte finish. I soak for 5 minutes. I don’t have a controller so the temp. does fluctuates some, but I keep a close eye on it. Does a 10-15 higher degree span make a difference during this time? I too would like to have a shiny finish. Thank you: your site and help is superb!

    Mary

    P.S. I use Reusche paints

    • Hi Mary,

      We all have to do whatever it takes to get the results we want. And maybe we each have to do things differently. Here’s a case in point: you fire your glass to 1250 F. / 675 C. and your results are matt. I fire mine to the ‘same temperature’ and mine are glossy. The most likely thing is our kilns are different. Now I don’t think you need to increase the soak beyond 5 minutes if all you’re after is making your paint look glossy. But I do think you need to raise your top temperature until you find the lowest temperature which gets you the result you want. So I’d suggest you cut off 4 squares of plain glass, do some fairly quick painting on each of them, then fire them one at a time, each time raising the temperature by 50 F / 10 C. Will you please let me know what happens?

      Best,
      Stephen

      P.S. You mention you use Reusche paints. One other thing: different Reusche paints need different top temperatures, so it is worth checking what’s recommended for the exact paint you have.

  4. I was looking at your website and was wondering where I would get a painting bridge? I live in London and do stain glass painting courses, but would like to do more painting at home. Many thanks Angie Caplin

  5. Just discovered your site and I love it!I wanted to reach out to you and see if you would be willing to test out some of my glass etching craft supplies for free for feedback. Any interest? I will ship the supplies to you all for free with cream and stencils. Looking forward to hearing your thoughts. I can’t wait to hear from you! Eric

    • Thank you very much for the offer, Eric. We’ve full hands already with clients and students. So it wouldn’t be right to venture down new avenues right now.

      Best,
      Stephen

  6. Fire-polishing a slumped piece.

    Hi,

    As I was cold-working a slumped bowl, the bowl slipped off the grinning wheel a few times and now I have some light grinding marks along the inside of my once shiny bowl.

    Do you think a fire-polish setting would allow those light marks to soften/disappear without causing the glass to heat up too much and continue to slump into the mold?

    Thanks!

    • Hello!

      I’m sorry: I just don’t know enough to answer your question or give you guidance here. Since you can’t run tests to identify a schedule which is hot enough to remove the marks but not so hot it distorts the bowl, whether you decide “to boldly go” depends on how visible the marks are and your own attitude to risk.

      Best,
      Stephen