How I Formulated a Cone 6 Silky Matte Glaze Using Insight-Live

I will show you how found a recipe on Facebook, assessed it, substituted my own materials, tested it, adjusted it. Now it is like a cone 10 dolomite matte.

A. Insight-live

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Silky Mattes are more difficult at cone 6 than at cone 10. It is common to find ones that either gloss on slight over-firing, are too matte, are not durable (they cutlery mark), ones that have a poor functional surfaces (and stain easily) and ones that craze.

I found this recipe on Facebook. Let's take a look at it in Insight-live.

Gerstley borate 9
Silica 30
Dolomite 17.5
EPK 20
Nepheline syenite 33.5
Whiting 2.5

Copy it, paste into Insight-live account, # as G2928

#1: Mattes need high Al₂O₃
-many recipes source most of it from feldspar, that brings in too much KNaO and crazing happens
-other recipes source it from alot of clay, the glaze shrinks and cracks during drying

Open G2571A beside.

-Silky mattes happen when Al₂O₃ and MgO are high, SiO₂ is low and the glaze melts well. Tiny surface ripples happen.
-At cone 10 it just happens. But at cone 6 it needs an extra kick with B₂O₃
-G2571A even has a little B₂O₃ (unusual but maybe a secret to why it works so well).
-At cone 6 we need more

Where do we get B₂O₃: GB (click it)
-This is going to have plenty of clay, we don't need GB gelling the slurry and shrinking it more (it is plastic)
Use a frit.

Open Roy Limits cone 6.
Compare limits again:
-MgO still not too high, Al₂O₃, SiO₂ good, ratio is good

Sourcing issues again:
-The MgO is sourcing from dolomite: No good for cone 6, will use talc, melts better, no gasing
-CaO from whiting: switch to wollastonite to avoid gassing issues
-Clay: Not looking for toilet bowl white. Going to use Ravenscrag Slip to get a slurry of the best possible application properties (as much as I can)

Let's improve this recipe.
Not going to duplicate, going to start from scratch

1. Start with 50 Ravenscrag, 10 Frit
-click on RSlip to show iron

2. Add 1 talc, show it, match MgO (to 5)

3. Highlight B₂O₃, reduce frit to match it (to 6)

4. Highlight KNaO, need it, add 5 nepheline syenite, show it, re-hilight KNaO, match (to 7)

5. Increase frit to rematch boron (to 7)

6. Add 1 wollastonite, show it (oversupplies CaO, will leave for a moment)

7. Need Al₂O₃, SiO₂. Add 1 silica, calcined kaolin

8. Add nepsy to 0.24, backoff (to 9)

9. Add 1 talc (to 6) to match MgO

9. Add frit (to 8) to rematch B₂O₃

10. Hi-light Al₂O₃, kaolin to 3.5

11. SiO₂ to 1.5

Look at the LOI! It is much lower on this new glaze, that means less change of glaze defects.

Retotal to 100
Reduce RSlip to 60, notice formula hardly changes. Why? RSlip chemistry is much more like a glaze than any of the others.

It tested it. Too glossy. Needed to add Al₂O₃, increased Al₂O₃ to 0.5+

Calcined kaolin a good way to adjust: why? Try it.
-Cuts Al₂O₃ and SiO₂ (increasing flux) and also increases the ratio a little.

Approximate final recipe:
Nepheline syenite 13
Ravenscrag Slip 60
Ferro Frit 3134 11
Talc 8
Wollastonite 1.5
Calcined Kaolin 9
Tin Oxide 5

Where is this going?
-Double layering
-Black matte

Mattes are fragile, glazes want to be glossy.
-It is important to have a way to adjust the degree of gloss so you can crank up the matte, then back off if it marks or stains
Frit 3134 only version also possible: show
Frit 3134/talc version: show

Links

Recipes	G2928C - Ravenscrag Silky Matte for Cone 6 Plainsman Cone 6 Ravenscrag Slip based glaze. It can be found among others at http://ravenscrag.com.
URLs	https://digitalfire.com/university/insight-live/overview/Insight-Live%20Overview.html Insight-Live.com Overview Video
URLs	http://m.youtube.com/user/tonywilliamhansen YouTube channel for Tony Hansen
Glossary	Matte Glaze Random material mixes that melt well overwhelmingly want to be glossy, creating a matte glaze that is also functional is not an easy task.
Glossary	Glaze Chemistry Glaze chemistry is the study of how the oxide chemistry of glazes relate to the way they fire. It accounts for color, surface, hardness, texture, melting temperature, thermal expansion, etc.

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
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