A Broken Glaze Meets Insight-Live and a Magic Material

Use Insight-Live.com to do major surgery on a feldspar saturated cone 10R glaze recipe with multiple issues: blistering, pinholing, crazing, settling, dusting and possibly leaching!

A. Insight-live


Click here to watch this at youtube.com or click here to go to our Youtube channel

This is an outline transcript of the video. Use the link below to go to the video itself.

The video is about this cone 10R rutile blue glaze (see close-up photo below) and how to fix its problems using ceramic chemistry:

G-200 Feldspar 54
Barium Carb 7
Whiting 11
Gerstley Borate 8
EPK 3
Silica 17
Red Iron Oxide 2
Rutile 6

1. We are going to fix a troubled glaze with a cool material (demonstrates the power of ceramic chemistry)
Copy and paste into Insight-live; Fix material references (show how to find G200)

2. An example of what people will "put up with" to have the fired result they want
-crazing, blistering, pinholing, settling, dusting

3. Survey materials
-too much spar - certain crazing
-barium - leaching issues, LOI!
-whiting - LOI!
-Gerstley borate - LOI, uncertainty about consistency
-kaolin: not enough
-Silica: looking lonely, only one who is has one what he should

4. Survery chemistry:
(Start calculation mode, mark iron and rutile as non-participant)
-expansion too high
-Al2O3:SiO2 too low - leaching (esp with barium)

5. So many ways to improve this!
Only going to do what is practical right now. Leave the crazing and the barium leaching issues for how, assuming it is non-functional
-Need to supply CaO, B2O3, BaO from non-gassers to reduce blistering, piholing
-For the slurry and drying issues I need kaolin. It supplies lot of Al2O3, the major contributor now is feldspar; need to reduce it to make room
-That will reduce KNaO, need to su pply it from something with low Al2O3 to retain room for the kaolin, and high KNaO to replace what is lost from the feldspar: Everything hinges on that.
The answer: a cool material: Frit 644 ... (show chemistry, click link to go to Digitalfire Reference library to see supplier)

6. Here is frit 644
Make duplicate to compare chems and recipes
Remove half of feldspar (to 25)
Replace whiting with wollastonite
Replace GB with frit 3134 (no going to do the barium right now)

7. Add the frit
Use calculation mode (turn off iron, rutile in copy)
(order from the material supplying the most oxides to one with the least)
-Frit 3134 for boron
-Frit 644 for KNaO (tolerating use of Na2O instead of K2O)
-Wollastonite for whiting
-Barium for BaO
-Kaolin for Al2O3
-Silica for SiO2

8. Frit 3134
9. Frit 644 (not going to get same K2O, Na2O, only total)
10. Wollastonite
11. Barium, kaolin, silica
12. Notice have lost the match on KNaO. refine. MgO.

13. Retotal

14. Glaze still has same chemistry, yet the recipes are totally different
-More complex but there are ways to simplify it plus resolve the crazing and possible leaching at the same time.
-but it should pinhole, blister less; dust less and suspend and apply much better.
-Now, how would you do this without ceramic chemistry?

We will ddress crazing, leaching later

Rutile blue glazes: Love the look, hate the trouble to make it

Rutile blue glazes: Love the look, hate the trouble to make it

A closeup of a cone 10R rutile blue (it is highlighted in the video: A Broken Glaze Meets Insight-Live and a Magic Material). Beautiful glazes like this, especially rutile blues, often have serious issues (like blistering, crazing), but they can be fixed.

In Bound Links

  • (Troubles) Glaze Blisters

    Questions and suggestions to help you reason out the real cause of ceramic glaze blistering and bubbling problems and work out a solution

  • (Glossary) Pinholing

    A glaze defect where tiny holes are present in the fired glaze surface. These holes normally go down to the body surface below. Pinholing is a plague in industry, the tiniest hole in the glaze surface of a tile or utilitarian item can make it a reject. Industry goes to great pains to get materials o...

  • (Materials) Barium Carbonate - BaCO3

    Barium Carb, Witherite

  • (Materials) Feldspar
  • (Troubles) Glaze Crazing

    Ask the right questions to analyse the real cause of glaze crazing. Do not just treat the symptoms, the real cause is thermal expansion mismatch with ...

  • (Troubles) Glaze Pinholes, Pitting

    Analyze the causes of ceramic glaze pinholing and pitting so your fix is dealing with the real issues, not a symptom.

  • (Materials) Fusion Frit F644 - High-sodium boron-free frit

    Frit F644

  • (Troubles) Powdering, Cracking and Settling Glazes

    Powdering and dusting glazes are difficult and a dust hazard. Shrinking and cracking glazes fall off and crawl. The cause is the wrong amount or type ...

  • (Glossary) Suspension

    In traditional ceramics, glazes are suspensions, not solutions. They are mixes of insoluble mineral, frit and/or stain particles that have been added to water to form a liquid useful in the ceramic process. That suspension is what confronts us in the bucket or tank, learning how to assess and contro...


By Tony Hansen




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