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 address crazing, leaching later.

Links

Materials	Fusion Frit F644
Materials	Feldspar In ceramics, feldspars are used in glazes and clay bodies. They vitrify stonewares and porcelains. They supply KNaO flux to glazes to help them melt.
Materials	Barium Carbonate A pure source of BaO for ceramic glazes. This is 77% BaO and has an LOI of 23% (lost at CO2 on firing).
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 of clay.
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
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.
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 the body.
Glossary	Suspension In ceramics, glazes are slurries. They consist of water and undissolved powders kept in suspension by clay particles. You have much more control over the properties than you might think.
Glossary	Pinholing Pinholing is a common surface defect that occurs with ceramic glazes. The problem emerges from the kiln and can occur erratically in production.

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.

Click here for case-studies of Insight-Live fixing problems

You will see examples of replacing unavailable materials (especially frits), fixing various issues (e.g. running, crazing, settling), making them melt more, adjusting matteness, etc. Insight-Live has an extensive help system (the round blue icon on the left) that also deals with fixing real-world problems and understanding glazes and clay bodies.

By Tony Hansen
Follow me on

Got a Question?

Buy me a coffee and we can talk