Matte glaze at low temperature too milky

[mr_glazy_man]

I have created a really lovely light Matt glaze at cone 03-04 using the following ingredients and percentages.

3134 - 40

Wollastonite - 30

EPK - 10

Silica - 20
—

Black Stain - 10%

 

For white and lighter pastel colours, the above formula works really well. But for the darker colours such as black, the formula is somewhat lacking in the sense that it is just too white. I have increased the amount of black stain to up to 10% of the recipe, and it’s still not that dark. I cant seem to get the really dark black. The whiteness is no doubt caused by the Wollastonite.
 

I’m wondering if anyone can recommend an alternative matting agent (aside from any of the calcium carbs) that will yield a matte finish at these low temperatures? 

[Min]

Glaze matting agents are alumina, zinc (less so) plus magnesium, calcium, strontium and barium which are all alkaline earths. For lowfire you don't want to use barium for sure, magnesium might be okay if it's in frit form. I haven't used strontium in a lowfire glaze, I strongly suspect it isn't a good choice either. Zinc should be okay and alumina will be okay, calcium you already have. Speed the kiln cools at also comes into play.

I ran your glaze through Insight glaze calc, this along with looking at the recipe plus your comments about the "whiteness" of it even with 10% black stain makes me think that this glaze is underfired at cone 04 - 03 and that is why it is matte. 

Have a look at the silica : alumina ratio (red arrow), see how it's coming in at 21 : 8.1? This means that if this was a well melted glaze it in all liklihood it would be very glossy. A look at the alumina (blue arrow) shows it to be quite low for a matte glaze, also I would expect the boron (pink arrow) to be higher for a well melted lowfire glaze.

If this glaze is for non functional work then no problem with it but if it's for functional work I would be working on another glaze. To try and answer your question about getting the black stain to make the glaze black I would be increasing the 3134 frit plus increasing the epk, but again I wouldn't use this on functional ware. What oxides make up your black stain might come into play also, if it contains chrome that will hinder the glaze melt also.

 

[mr_glazy_man]

This is a really in depth response - thanks so much for that. Next recipe I’ll try will be the below:

3134 - 50

Wollastonite - 15

EPK - 30

Silica - 15

[Min]

Have to try it and see how it does, on paper it comes out between a matte and a gloss. If you want another to try I would suggest the one below if you have access to Ferro Frit 3195. Another helpful thing to do would be to put your second recipe into Glazy and see how the formula compares to the one below and other ^04 satin or matte or gloss glazes. Taking time to do this could save some time with glaze testing.

It's difficult to know how much knowledge someone has with glaze testing and chemistry, sorry if I've over or under simplified this.

 

 

[mr_glazy_man]

This all makes perfect sense @Min.  I understand the underlying chemistry quite well, but am still quite new at blending ingredients to yield the results I want. In this respect, your knowledge and time helps me greatly. I'll give it a whirl and let you know how it goes.

[Bill Kielb]

20 hours ago, mr_glazy_man said:

understand the underlying chemistry

some very general rules that may help
In general 7:1 SI:AL is highest gloss under old Stull so mixing glazes let’s say from 3:1 to 5:1 often gets you some form of true matte, which is always a matte even over fired it is a runny matte. As this ratio approaches 7:1 and beyond it generally becomes glossy so: +5:1 to 12:1 generally gloss glazes and highest gloss in and around 7:1. The benefit of knowing the expected texture it often points out when expected to be a gloss but fires matte, something is likely wrong as ……. it’s simply under-fired. For true mattes, simply adding more silica will take them toward gloss.

Flux ratio
R20 of 0.3:0.7 oftentimes thought of as ideal for durability and probably as low as 0.2:0.8 still decent indicator of durability. Much higher than 0.3:0.7 or lower than 0.2:0.8 often can indicate likely non durable chemistry.

Boron (in general)

0.45 gets you a cone 04 melt, 0.15 gets you a cone 6 melt. This can be helpful if you are way under or way over, it's likely not ideal. Fairly simple boron requirements here: https://www.ceramicmaterialsworkshop.com/uploads/5/9/1/2/59124729/katz_tf_boroninglazes_0912.pdf

Edited August 26, 2022 by Bill Kielb

[mr_glazy_man]

This is great, thanks @Bill Kielb. I have actually reglazed using the above formula, but with 3134 instead of 3195. It went into firing this evening. I’ll post results tomorrow.

When you say “old stull”, what do you mean? “Old” relative to what? 

[Bill Kielb]

2 hours ago, mr_glazy_man said:

When you say “old stull”, what do you mean? “Old” relative to what? 

RT Stull - a long time ago (Ray Thomas Stull, 1875-1944) understanding the Stull chart: https://wiki.glazy.org/t/understanding-the-stull-chart/857.html

BTW if you put your glaze in a calculator, you will know some of those numbers which can give you an expectation of the melt.

 

Edited August 30, 2022 by Bill Kielb

[PeterH]

In case it's of any interest, this pdf includes a reprint of the original Stull chart paper. https://tinyurl.com/nhz64wy3
... and a reprint of "Cobalt colours other than blue".

[Min]

7 hours ago, mr_glazy_man said:

I have actually reglazed using the above formula, but with 3134 instead of 3195. It went into firing this evening. I’ll post results tomorrow.

 

Have a look at the differences between the two frits. Big difference between the two is Ferro 3134 contains very little alumina and about double the sodium plus a fair bit more calcium than Ferro 3195.

BTW Ferro 3195 at 85% + 15% kaolin will make a fairly glossy ^04 glaze with nothing else added. 

So, with that in mind you can predict how your altered recipe might turn out. Have a look at the formula chemistry plus the silica : alumina ratio on the right side. Take a guess at how you think this will differ from the original.

 

 

 

 

[mr_glazy_man]

Very true. I should have upped the EPK significantly to compensate, amongst other things. My issue is that I don’t have any of the 3195 at the moment. 
I don’t expect a fantastic result (it will be likely come out glossier than I hope), but I will post it here nonetheless.

[Min]

Do you have any source of boron other than Ferro 3134?

[mr_glazy_man]

On hand, I have 4131, 3124 and 3110. I could have used the 3124 instead of 3134 for the additional stabiliser as the 3110 is high sodium. What would you recommend?

[Bill Kielb]

30 minutes ago, mr_glazy_man said:

3110 is high sodium. What would you recommend?

Just a thought …….. don’t be afraid of reducing your raw silica to get your si:Al ratio towards more matte. Often worth a simple line blend reducing silica to see the effect. Glazy has a free calculator that you could sub materials out, rather than guessing types and quantities.

[Min]

6 hours ago, mr_glazy_man said:

On hand, I have 4131, 3124 and 3110. I could have used the 3124 instead of 3134 for the additional stabiliser as the 3110 is high sodium. What would you recommend?

This is a tricky one! I found an analysis for 4131 on Glazy here, I don't know if it is accurate or not. @Babs are you familiar with this frit?

If the Glazy analysis is correct the closest I can get it using the ingredients you have is below.  Note the calcium is lower but the flux ratio is better. On paper this looks okay but won't know for sure how it will turn out until you test it. Going forward if you can get Ferro 3195 in your part of the world it might be worth picking some up.

If you find this is too matte then you can do a line blend with a clear glaze or try increasing the silica. There is a limit to the amount of silica that can be added without harming the melt though, again it takes some testing. Like Bill said a line blend is a good way to test increasing or decreasing silica (or any material). If you try this one I would fire it on a waster slab  / cookie just in case it runs.

 

 

Edited August 31, 2022 by Min

[Babs]

This is Digital info, but on sale Aus.

https://walkerceramics.com.au/products/materials/frits/ gives anslysis and subs/ replacements.

 

[Bill Kielb]

4 hours ago, Min said:

If you find this is too matte then you can do a line blend with a clear glaze or try increasing the silica.

Here is a interesting guess and why: everything with more than 0.45 boron will melt at 04 and with sib:Al of 7.0 will fire as some form of gloss. The relatively high alumina 0.56 ish will make these fairly stiff and maybe difficult to melt at 04 though so there is the possibility of an underfired matte. Just a guess though interesting to see how they all fire.

Edited August 31, 2022 by Bill Kielb

[mr_glazy_man]

Hi team,

I’ve gotten the below recipe out of the kiln.

3134 - 50

Wollastonite - 15

EPK - 30

Silica - 15

As you all predicted: gloss. It also seems overfired to me. I have another test currently firing at two cones lower. 
@Min I’ll give the 4131 test a whirl tomorrow

 

 

Edited August 31, 2022 by mr_glazy_man

[mr_glazy_man]

3 hours ago, Bill Kielb said:

everything with more than 0.45 boron will melt at 04

I suppose it therefore stands to reason that as you go up in boron, you melt lower and lower until you reach it’s melting pint?

[PeterH]

10 minutes ago, mr_glazy_man said:

I suppose it therefore stands to reason that as you go up in boron, you melt lower and lower until you reach it’s melting pint?

An oldie from when  people were moving from cone 10 to cone 6.

Boron in glazes
https://www.ceramicmaterialsworkshop.com/uploads/5/9/1/2/59124729/katz_tf_boroninglazes_0912.pdf

 

[Bill Kielb]

1 hour ago, mr_glazy_man said:

I suppose it therefore stands to reason that as you go up in boron, you melt lower and lower until you reach it’s melting pint?

Yes but too much boron has its own issues. Earth geology basically melts at cone 10 so not really a need for boron there.

2 hours ago, mr_glazy_man said:

As you predicted: gloss

My suggestion: do some tests lowering the Si:Al or in your case sib:Al and observe how it becomes more matte as the ratio falls to 5:1 or less to better understand this ratio and the effect it has on a true matte.

The Glazy link I posted above has Peters chart and a paper written by the guy who created that chart (Matt Katz, 2012). Also has some great references to other research that may prove interesting. You might want to open it and give a once over.

https://wiki.glazy.org/t/understanding-the-stull-chart/857.html

Here is a quick Katz intro video where you can learn a bit more about Stull. It contains the screenshot below which illustrates things fire by composition which means if you raise the amount of  Alumina high enough it will require more heat to melt. Your glazes have been fairly high in Alumina so they ought to fire stiff by composition. https://youtu.be/-oRFAxpmaqE

 

Edited August 31, 2022 by Bill Kielb

[Min]

Thanks Babs, that's the same analysis as what the Glazy link had that I used so all is good.

@mr_glazy_man, if you oversupply boron you can get some really interesting glaze effects but if it is far in excess of what is needed to get a good melt then you will get a "soft" glaze plus the likelihood of crazing increases even though the expansion figures will decrease.

Having plenty of both alumina and silica in a glaze is very beneficial to having a durable glaze as long as there is enough boron and fluxes to melt the glaze. If there is room in a glaze to add either more silica or alumina (or both) without loosing the qualities of the glaze you are looking for then it's a good idea to do so as far as a durability standpoint.

Edited August 31, 2022 by Min

[mr_glazy_man]

I honestly feel like I’ve learned more from this single thread than all my research.  Some incredible information here.

I’ll keep you all posted with progress

[Min]

12 hours ago, Bill Kielb said:

Earth geology basically melts at cone 10...

I've noticed you have said this a few times in various threads, would you mind elaborating on it? Not trying to hijack this thread, if it's a complicated answer or one that is likely to elicit responses maybe a new thread explaining it?

Thanks

 

" @Min I’ll give the 4131 test a whirl tomorrow" 

Good stuff, it's the only way to know which direction to head in as looking at formulas will only get you so far, it always takes testing. I would suggest to do a test tile without the stain then dip and tile then add the stain for a second one. 

Edited August 31, 2022 by Min

[Bill Kielb]

43 minutes ago, Min said:

I've noticed you have said this a few times in various threads, would you mind elaborating on it?

Yes, Not meant to be complicated or elaborate I think it’s a reminder that cone ten is a thing because of our geology, we often do special things to make cone ten glazes melt at cone six or less.