glaze that settles rock-like quickly

[grackle]

HI all:  I mixed a new glaze sample today.  Have been looking for a good cone 5-6 white, and found this one on Glazy.   

Silica   31

Fer Frit  30

Custer feldspar  28

Whiting  14

EPK

[grackle]

did not finish

EPK  7

Bentonite  2

Glaze ingredients immediately settled into a rock, and no amount of stirring helped,, it just did the same thing!!  The ferro frit was 3110, a frit i have never used before, and wonder if that had something to do with it.  HOping someone can help.

2 minutes ago, grackle said:

HI all:  I mixed a new glaze sample today.  Have been looking for a good cone 5-6 white, and found this one on Glazy.   

Silica   31

Fer Frit  30

Custer feldspar  28

Whiting  14

EPK

 

[Mark C.]

Magma is what is needed-it will flaot bricks

here it is

https://shop.brackers.com/magma-miracle-anti-gravity-multipurpose-additive/

[Bill Kielb]

1 hour ago, grackle said:

thing!!  The ferro frit was 3110, a frit i have never used before, and wonder if that had something to do with it.  HOping someone can help.

Usually if something has 10-15% clay the clay will help suspend. Sometimes up to 2% bentonite can help. The bentonite doesn’t really add to the fired glaze and 2% is often the practical limit. If you love this recipe, then likely magma, else you might just find a different composition. Getting as much of your necessary silica, alumina and fluxes from the clay can be argued as an efficient use of materials rather than using suspending agents. The 3110 is likely there for the boron to melt at cone 5/6.

Edited September 29, 2023 by Bill Kielb

[grackle]

hmmmm...since this is just a sample, i am inclined to try a different white.  not sure why it seems so hard to find  good whites???

[Min]

1 hour ago, grackle said:

not sure why it seems so hard to find  good whites?

What qualities are you looking for in a white glaze?

[Callie Beller Diesel]

21 hours ago, grackle said:

why it seems so hard to find  good whites

I have been summoned!

What Min said: what do you want in a white, and what clay are you using it on? Give me an idea of what look you’re trying to create. 

[Roberta12]

I have tested 4 whites from Glazy.  And one from another source.  All of the whites were great on porcelain, white stoneware, speckled buff and light brown stoneware.  However I have only found one that seems to cooperate on dark brown (high iron) stoneware.  As @Min and @Callie Beller Diesel have asked, what do you want in a white and what clay are you using?  It has made a lot of difference in my tests.  And I try to find a glaze that is in a sweet spot on that UMF chart.

 

[grackle]

Thanks, guys--have been away from the computer.  I am looking for a satin white, that will work on either my Cinco Roja clay or my Cinco Blanco clay from Armadillo Clay in austin, TX.  I also work with the Nara Porcelain from Aardvark (I think).  All cone 6 clays, but to be honest, I fire to Cone 5 because I have determined my L and L kiln fires a bit hot., based on repeated cone results.  I like to use stains with the white glaze.

[grackle]

The Cinco Roja is a medium red brown, and the Cinco Blanco is white, but not as white as the Nara.  I have been  messing with a very dark, almost black brown clay, but have recently decided the minuses of using it outweigh the positives.  It tends to bubble when fired, and it stains everything it touches.  photo of the bubbling below

[Roberta12]

@grackle  As I am sure you have heard before, test test test.  That is why I have several batches of white sitting on the shelf staring at me.  I was trying to find a white that would work well on New Mexico Chocolate clay.  I may have one now.  It's a shiny white, but I may go with it.  My other strategy is to use either white slip or white underglaze and put clear over it for the glaze firing.  I have a clear that works really well on the dark brown.  But because I like to punish myself, I do work with other clay bodies that run the gamut.  I have been looking for a nice satin myself.  I have a white semi matte that is pretty good, on everything  but the dark brown clay.  Let me know if you want the recipe. 

Oh and I have dialed back to cone 5 as well, my kiln seemed to be firing a bit hot.  I was getting serious bloating with the dark brown clay.  

Roberta

[grackle]

Thanks, Roberta:  I would love to have the recipe.   I always test any new glaze on my various clay first.  I got several of the recipes I used in college (many years ago) from the pottery dept there, but for some reason, they no longer had the white.  The college used the same clay I am using now, so it seemed logical.  I read something about  those dark iron rich clays needing more oxygen in the bisque fire to burn off more carbon and prevent bloating.  I have a downdraft kiln  which supposedly has enough oxygen, but do not know how to introduce more except by leaving peepholes open?.

[Roberta12]

This one is my favorite on buff clay.  Or light brown clay.  I am still in the semi testing phase. 

Off White Semi Matte  (you can find it on Glazy.)

FF3134        28.0

Silica               16.0

Talc                    15.0

EPK                    14.0

Ravenscrag Slip     13.0

Ravenscrag Slip Roasted     13.0

 Zircopax            7.0

 

[Min]

@grackle, for dark clays or those with a lot of impurities to burn out it's important to slow the bisque firing down between 1300F through to 1650F. It's in this temperature range inorganic carbons will burn out. Try slowing your bisque firing down 60 -100 degrees F per hour and see if that helps. For dark clays coloured with manganese try firing to only cone 5.

Another way to get a nice matte glaze and be able to adjust how matte you want it is to blend a gloss glaze (without colourants or opacifiers) with a quite matte glaze. If you do a simple line blend with the gloss and add increments of 10% of a matte glaze you can see how adding the matte will negate some of the gloss. If you want to try this a good recipe to use is this one. Once you have the level of mattness (if that's a word) you like then add zircopax (approx 10%) or tin (approx 5%). If you find the zircopax makes it too matte (because it adds silica also) then tweak the gloss slightly higher.

[Roberta12]

@Min  I have heard tales of mixing matte and gloss to achieve the look you want, but I have been reluctant to try that.  Thanks for the great link! 

[dhPotter]

@Roberta12 This mixing matte and gloss works great!! I have a base of G2934 at 40% and a clear, G1216M, at 60%. This base has given me white, tan, yellow, turquoise and gray liner glazes. The glazes are very durable. 

Edited October 3, 2023 by dhPotter

[Callie Beller Diesel]

I’m a big fan of Ravenscrag slip in recipes, but I can get it easily. It should be able to be special ordered in the US from anywhere you can get Alberta slip from. They’re from the same supplier. It gives a good white gloss over the red clay I use, but you want a satin. 

Currently I’m doing some testing on Sue’s Calcium Matte from Glazy, and trying to take it into satin territory. It’s got really great colour response, but I’m finding it crazes a bit, and the iron tests  discoloured with vinegar overnight. I’ve got a line blend with silica going into the kiln next week that I hope will address those 2 problems. I can share results in about a week and a half from this writing. 

 When creating a white over red clay, if you have a glaze that already has the flow and application characteristics you like, mix a batch without the usual colourants and add 7-10% total opacifier instead. I prefer to mix opacifiers, because it tends to make for a more interesting glaze. I like titanium and zircopax, or tin and zircopax, usually just a 50/50 split. If you do this, use at least a small cup for a test tile. Using the usual 2” extruded guys won’t give you enough of an idea of the subtleties that will show on your main body of work.

In choosing a base glaze, think about whether or not you want to completely obscure your red clay with the white glaze, or if you want some texture to show through. If you want some texture, a well melted or slightly fluid glaze will be better. If you want a more majolica look, look for something stiffer. 

[grackle]

Thank you all!  Roberta, Min and Calle:  I can see I have a LOT of testing and trying different things to do!!  Will be working my way thru all of this (albeit slowly).  I have yet to understand completely all that you have suggested,  especially in terms of additions and subtractions.  One thing at a time, I think!!

Grackle (Sandra)

[Callie Beller Diesel]

Getting a white glaze is easy. Getting a nice white glaze involves a bunch of fine tuning. 

 

2 hours ago, grackle said:

have yet to understand completely all that you have suggested,  especially in terms of additions and subtractions

I appologize! Where did I loose you, and I’m happy to backtrack. There are no stupid questions. 

[grackle]

Hi Callie:  No apology necessary!  While I have often done line blends with different glazes, I have not really studied what the individual glaze components do (or not do), so I will just need to study the suggestions slowly and methodically.  My husband and I often joke about the fact that he is the logical one, and I tend to think more laterally (sideways).  We often reach the same conclusions, but come at things from 2 different directions, and I think I am that way with glazing too.  

Will holler if I have questions!

Thank you, Sandra (aka Grackle)

[grackle]

ok, Ravenscraft slip.  Where do I get that?

[Roberta12]

7 hours ago, grackle said:

ok, Ravenscraft slip.  Where do I get that?

I get it from my clay supply house.  I have seen it listed at different clay supplies online.  Check with your clay supplier.  

[Hulk]

Looks like Axner has a good per pound price.

I'm not seeing that suppliers near me (Northern California) carry it ...Claypeople in Richmond has it.

[grackle]

thank you!  found some at Baileys.

[Callie Beller Diesel]

First of all, don’t feel bad for not knowing what the different components do. There can be a lot of moving parts that determine what each thing does in relation to the others. Chemistry is about proportions, and changing proportions will change the results. Lateral thinking in this instance is not a detriment, because whether or not a result is “good” or “bad” depends on context. Some people want a crawling beads glaze for special effects, but on the inside of a serving bowl it’s a defect.

The easiest way to go about this with your level of chemistry understanding is to start with a glaze of any colour that has the sheen level and bucket qualities that you already have experience with. This will eliminate a lot of testing variables and points that need refining.  If you don’t have a suitable candidate, the base that Roberta provided is a good starting place. 

You would then take any colouring oxides out of it, leaving you with what we’d call a base glaze. Colouring oxides are metals like iron, manganese, cobalt, copper, chrome, etc. Anything with a very noticeable colour to it. Rutile is also in this category, because it’s a combination of iron and titanium, with trace quantities of other stuff.

Then you want to replace those colourants with one or more opacifier. Which ones and how much depends on how opaque the glaze needs to be, and whether or not you want the clay to peek through on the high points or not.

 In pottery glazes, there’s 3 things that can be used as opacifiers: Tin oxide, Zirconium compounds (usually zircopax in North America), and titanium dioxide. Tin needs to be used in larger quantities (8-10%) to be effective, which can be an issue due to the price. But it gives a softer, very aesthetically pleasing white on it’s own compared to the other 2.  Zircopax is less expensive and gives a very stark, bright white with not a lot of visual variance. It can also stiffen a glaze, which may or may not be desirable. Titanium is technically a variegator, which means in smaller quantities (1-3%)  it’ll give glazes that floating blue effect, which is called phase separation. But if you use more of it, (7-10%) it’ll give you an opaque yellow, or even orange colour. Using it by itself won’t get you a proper white glaze, but it can add subtle visual interest. 

To fine tune your white glaze, start with a line blend of your base glaze with one opacifier each. You want to find out what the ideal amount of each opacifier is to get the coverage you want without having the end result use more materials than you need. This doesn’t need to be too extensive: 3, 5, 7 and 10% increments will give you enough info for this. If you find your ideal glaze in this round of testing, you can carry on with making your work. Be sure to use small cups as test tiles to get a better idea of what each glaze will do when actually in use. If the sample size is too small, they’ll all look the same. 

Once you’ve determined your sweet spot for each opacifier separately but nothing’s really calling your name yet, do a triaxial blend with the 3 opacifiers. For a really nice description on the least painful way of doing this, I recommend Derek Au’s article here.