Looking to replace to Laguna 55 or 65

[Pat B.]

I have been using Laguna 55 for years and love how non-fussy it is although it is a bit groggy and doesn't fire too white. I recently started using Laguna 65 and love how smooth it is and the white color, although  attachments do crack a bit more and I'm told it doesn't play well with a lot of glazes because of the low COE.

Problem: I no longer live near a supplier who carries those two clays. I do live an hour away from Sheffield Pottery and an hour away from Bailey Ceramic Supply. Can anyone recommend a cone 6 white stoneware? I'm not interested in B-mix 5 (my glazes want cone 6 and I don't want to deal with cracking and fussiness). I've seen negative things about Bailey's clay (bloating) but don't know anything about Sheffield's clays.

I appreciate any help.

[Min]

Haven't used Sheffield or Bailey claybodies so I'm no help making a recommendation. Hopefully someone will chime in here with their recommendations.

I do have a couple pieces of Bailey equipment (mixer/pugger and wheel), I've found their customer support is really good so I'm a bit surprised to hear about their clay having issues with bloating. Did they offer any help with the issue?

[oldlady]

pat,  you have not said whether you do wheel work or handbuilding.   some clays are suitable for one but not the other.  

i use an east coast clay, Highwater Little Loafers which is a white clay but not as white as porcelain.   it is good for both.   it has a low coe, something i know nothing about.  Min has been extremely helpful in suggesting recipes that work on it.   

it throws very well and i have been doing slab work for a number of years with it.   depending on what you want to do, it might be just right.  

[Lynn Hoffmann]

I find this clay to have other problems, but they are outweighed by all the positive things such as the absorption rate, and the shrinkage rate. And the price. I’ve never had glaze problems with this clay, and I’ve been using thousands of pounds of it for probably five years.

[Lynn Hoffmann]

Also I /and my students use 20 dipping glazes, stroke and coat, and some other cone 6 paint on glazes. Probably 5.000 pounds of this clay in the last 5 years. I wonder why you are having this problem and what glazes you are using. 

[Marilyn T]

Thanks for putting this forward Lynne. I also use Laguna # 65 (WC609) and am struggling to find glazes that fit.

I am interested in the COE range of glazes from potters who have successfully used Laguna #65 so that I can dial down (or up) the range of glazes I am presently considering for kitchen use.  

Background:

1.  I glaze fire at ^6 bisque ^04.  I mostly use the slow cool cycle with top temp 2185 (two holds on way down).   I also fire ^6 on some of the glazes (such as Rutile Green) as it gives a better colour.  

2.   The only one that has visibly crazed on me in this range (when glazing both sides of the piece) was (6.82) Chun Celadon from the book Amazing Glaze.  I did get some crazing on glazes at 6.52 (Glossy Base Glaze #1 from MC6)  if I only glazed the outside.  

3.  I haven't oven/ice water stress tested my glazes yet on this clay but am concerned as some of the glazes are giving a thud sound (delayed crazing) after being in use for a period of time.    

 

Edited April 4, 2023 by Marilyn T

[Hulk]

In my (limited) experience, calculated COE values are helpful to compare a glaze against a reformulation of the same glaze - where the ingredients are adjusted, and/or where a new ingredient is substituted in part.

Calculated COE values may be less helpful when comparing glazes of very different formulation.
My glaze lineup supports this, where the results don't line up with the numbers, exactly. There are a few outliers in my lineup!

Hope someone using the clay in question (WC-609) can offer some specific glaze suggestions.

As for other white stoneware (Pat B's question), I don't have any East Coast suggestions, however, here in California I'd found Clay Planet's Venus White a viable solution to my liner glaze crazing problems**, then IMCO's DC 3-5 white stoneware. IMCO is a short detour off an annual route, so I've bought more of that and am planning to continue with it (also their Red Velvet Classic and the WC-403).

Last material load, I bought one bag of WC-403 (Cone 5 Speckled Buff).
I'm very pleased with the results - my liner glaze and colors fit it well, it's a pleasure to work with, and other "problem" rate* is very low.
 

*where random pinholes and crawling are likely related to inconsistency in the clay.

**I was getting closer to fitting some another white stonewares - the craze lines getting further apart - then found Venus White, voila! Fit!

Just shout if you'd like to see my in production low COE clear (clear-ish, it has enough zircopax to make it milky white).

 

Edited January 31, 2023 by Hulk
offer to share low COE recipe

[Min]

2 hours ago, Hulk said:

In my (limited) experience, calculated COE values are helpful to compare a glaze against a reformulation of the same glaze - where the ingredients are adjusted, and/or where a new ingredient is substituted in part.

 

+1 for this. COE values are extremely helpful when adjusting a glaze by increasing or decreasing one or more ingredients that already exist in the glaze. Throw in another material or look at a different glaze recipe and you now are working with an entirely different glaze with its own dynamics. 

23 hours ago, Marilyn T said:

2.   I have successfully used glazes from COE( 5.9) Folk Art White to COE (7.3) Raw Sienna.  The only one that has crazed on me in this range (when glazing both sides of the piece) was (6.82) Chun Celadon from the book Amazing Glaze.  I did get some crazing on glazes at 6.52 (Glossy Base Glaze #1 from MC6)  if I only glazed the outside.   All of the successful glazes passed the usual hot water, oven, freezer tests but two of the bowls (one in Spearmint (6.8) and one in Powder blue (6.6)) didn't give a "ping" sound about one year after putting them into kitchen use even though there was no visible flaws.  The rest of the ware in these glazes passed the "ping" test.  My absorbancy tests range from .8 to 1.2%.  

Can't just look at one number or range and expect all glaze formulas within that range to fit. In addition to the different oxides contributing different properties and melts you also have to look at the type of glaze it is in regards to both opacifiers, colourants and cooling.

If the Spearmint or any of the other glazes that are matte or semi-matte  then COE numbers are not valid at all as some of the matting agents (like the calcium in Spearmint) will precipitate out the glassy matrix onto the surface of the glaze causing the semi / matte surface. By the calcium doing so you have created a microcrystalline glaze, COE calculation figures only work with a fully melted gloss glaze. Same reason why looking at a clay body recipe in glaze calc the COE figures means nothing given that clay is a crystalline material and not a fully melted gloss glaze.

Re colouring oxides and opacifiers. Some glaze materials, like zirconium, will give you a higher calculated COE figure but this is only looking at theory and not practice. In reality zirconium does not enter the melt therefore the change it imparts in the COE figure is skewed. Zirconium particles act like miniature boulders in the glaze and if a craze line starts the zirconium boulder stops the craze from propagating.   Many colouring oxides and titanium / rutile will also decrease crazing. Boron is another good example of how glaze calc doesn't show the entire picture, in theory you could increase the boron to really lower a COE but in practice if you go beyond a certain point crazing will increase. I would suggest looking at the properties of each glaze material and what the contribute to the glaze, look at COE figures for each of the materials. If you see a formula with high amounts of sodium and or potassium chances are it's a high expansion glaze that will probably craze on a low expansion clay. Look for recipes with low expansion fluxes like magnesium, lithium, moderate amounts of calcium plus good levels of silica and alumina versus ones with higher expansion fluxes and low levels of silica and or alumina and for cone 6 boron around 0.15 

 

 

 

 

 

 

Edited January 31, 2023 by Min

[Marilyn T]

On 1/31/2023 at 9:32 AM, Min said:

I would suggest looking at the properties of each glaze material and what the contribute to the glaze, look at COE figures for each of the materials. If you see a formula with high amounts of sodium and or potassium chances are it's a high expansion glaze that will probably craze on a low expansion clay. Look for recipes with low expansion fluxes like magnesium, lithium, moderate amounts of calcium plus good levels of silica and alumina versus ones with higher expansion fluxes and low levels of silica and or alumina and for cone 6 boron around 0.15 

Thank you for your knowledgeable response.  I will continue to read up on this.  

Two months later update:  Tried several transparent glazes* at decreasing COE but all of them failed the oven to ice water test on cups glazed only on the inside.   The lowest COE was 5.5 which was Robust E from John Britt's book.  The craze lines were wider apart than the other glazes I tried.   (note: the clay COE is 4.8).  In more testing, I increased the silica/alumina in the Robust E by 5%/4% and 10%/8% and also did a batch with + 5% tin oxide in a third test cup.  The best result was the 5%/4% increase of silica/alumina.  (picture of inside bottom of cup below).  The single craze line is around the edge of the inside of the bottom of the cup.  

What I didn't try is Min's suggestion of:  lowering the sodium and potassium and replacing those fluxes by increasing the magnesium (from the talc) and probably adding some lithium (from spodumene).  

At the present time I've decided to use up the remainder of this clay for non-utilitarian ware and switch to a new clay for my tableware.   

*. Min's clear; G1315U, G1215U modified, G2926S, G2926B, Robust E (all failed stress test) on this clay.   

 

 

 

Edited April 4, 2023 by Marilyn T
Updated.

[Min]

Quick comment about ^6 electric fired chun glazes and achieving a chun effect (that is to say a glaze that relies on a scattering of light to achieve a blue colour), it is going to be really difficult to achieve a true chun effect in an electric kiln at ^6. I haven't seen that glaze so I don't know how it compares to a high fire reduction chun. How close are the crazing lines with this glaze? (closer they are the more altering the glaze needs and/or might require so much changing that it won't really resemble the original glaze) BTW a really good article on Chun glazes and a recipe for a ^6 one here. Article is behind a paywall but you can access 3 free articles a month. I've posted the recipe from this article below, credit to Ryan Coppage and Ernestine Sitkiewicz. Do note that the clay used in Ernestine Chun is Laguna Frost which will take high expansion glazes well. 

Second glaze, again, how bad is the crazing? If it isn't too bad I would look to increase the alumina and silica by a ratio of 1: 1.25 of epk : silica. See how high you can get the silica and alumina and still have a good melt then test for crazing. If that isn't enough I would be looking to lower the sodium and potassium and replace those fluxes by increasing the magnesium (from the talc) and probably adding some lithium (from spodumene). I would also be using 325 mesh silica in recipes. Have a look at some low expansion clear glaze recipes and see how the formula differs. You can get away with having higher boron that 0.15 if there is plenty of silica and alumina in the recipe and still have a durable glaze. Keep an eye on the silica:alumina ratio while you are tinkering with it.

Keep in mind that not all glazes can be adapted to fit all clay bodies. There are many glazes that need so much tinkering that the new glaze won't bear much resemblance to the original recipe. Also, the type of fluxes used have an effect on colourants, sometimes noticeably. As an example I'm guessing your ^6 electric chun recipe would give a turquoisey / aqua colour?  In many other glazes copper will give a green.