Formulating a Cone 6 Silky Matte Glaze at 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

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

Silky Mattes are much more difficult at cone 6 than at cone 10
They are fragile: It is common to find mattes that either gloss on slight over-firing or are too matte and cutlery mark, stain and craze

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

Have been searching for a cone 6 silky matt. Wondered whether possible like at cone 10.
Found this one on facebook.
Problems with matte recipe found online:
-gloss on slight over-firing,
-too matte and cutlery mark,
-stain easily during use,
-they craze.

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

Out Bound Links

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