Help Needed with Glaze Recipe - MarieP

[MFP]

Hi!  I am starting to do pottery again after a 35 year hiatus. I used to have a wonderful, simple white glaze that matured from cone 1-10 and was good in either atmosphere. The recipe was 50 Colemanite, 50 something, 15 zircopax and 2 bentonite. I can't remember what the stiffener was. So if anyone knows this recipe, I would appreciate knowing what my missing 50 is. It was so simple that I didn't write it down in my glaze book of course! My brain keeps trying to tell me it was ball clay but that makes no sense. Any help would be most appreciated! 

[liambesaw]

I'm gonna guess EPK?

[Min]

Hi Marie and welcome. There is an old gerstley borate recipe for cones 04 - 6 that is 50 gerstley borate, 30 epk and 20 silica plus colourants or opacifiers to taste. Any recipe with 50% gerstley is going to really gel up in the bucket, won't need bentonite. Caveat though, with such a high amount of boron from the gerstley borate this won't be a durable glaze. There are frits available to supply  boron that won't have some of the issues with high boron glazes like the one I wrote above. Colemanite is no longer available. I can't think of anything that would be 50 gerstley borate plus 50 of something else that would make a durable balanced glaze. What are you looking for? A white glaze for ...?

[Tamas]

This Val Cushing recipe is 50% GB, 50% EPK, if you add the Zircopax you get the white. Not sure about the durability though

 

https://glazy.org/recipes/1213

[Bill Kielb]

39 minutes ago, Tamas said:

This Val Cushing recipe is 50% GB, 50% EPK, if you add the Zircopax you get the white. Not sure about the durability though

 

https://glazy.org/recipes/1213

Super high Alumina, fairly low silica, super high boron.  Lots of gerstley, lots of clay. Should fire matte but likely with so much Boron fires somewhat glossy. Lots of recipes out there though.

[neilestrick]

There are definitely better recipes out there. What cone are you firing to? What type of clay are you using?

[MFP]

Thank you all so very much for your responses. I am new to this and not sure how to respond to people individually. It was either EPK or Silica.  I don't quite understand the comment about durability....I have a 35 year old piece sitting in my garage with this glaze on it and it looks the same as the day it came out of the kiln. This glaze had a huge maturing range and had a nice semi gloss finish with small dark spots....even in heavy reduction with wood ash. It took oxides very well. It had a nice clean appearance. It was a nice one dip glaze that stayed put and was really nice for doing things like Chinese brush on, with minimal blurring.  It was also literally a nonstick surface....for the insides of casseroles.....nothing stuck to it.  It did need bentonite or it would settle out. Does that mean we are incorrect about the EPK?  We mixed up five gallon buckets at a time.    I was previously using a grey clay body with 2% iron. I now have a white clay body with grog from clay art that has an 04-10 range. My interest in resurrecting this glaze was that it is fine at either 6 or 10. I am imagining that it is even more white in an oxidation atmosphere.  I have hopefully attached a picture.

All my firing was cone 10 reduction.....with  18 inch cedar sticks pushed into the ports for four heavy reductions from 6-10.  It was a 20 cubit foot sprung arch down draft. I have a cone 10  Olympic electric and  cone 10 updraft now.  All your input would be appreciated.  

Anyone know a good substitute for Kingman feldspar?  When the buckets of glaze I have packed around for 30 years are gone....it would be nice to know how to replace them. 

[Mark C.]

I think all the spots are from the clay body. Not the glaze.

The glaze looks like any oatmeal glaze of that time on an iron bearing claybody

My honey white is similar . I foire to cone 10 reduction

The huge range of glaze melt from cone 6- to cone 10 is a larger issue . I have no info on that glaze. My honey white does not look good at cone 6 

I use kingman every week but I bought 3,000#s in 1982 from the mine-I'm on my last 400#s now-hopefully it will last until I'm done.\

You should be able to make that glaze with custar feldspar or any potash spar

How about talking to any of your 35 year old potter friends from that era for that reciepe??

You can toggle thru glazy on the web for a look alike. Remember its on a iron bearing clay body .

I have  glaze like that buts its cone 10  only not cone 6.

 

[Min]

14 hours ago, MFP said:

I now have a white clay body with grog from clay art that has an 04-10 range. My interest in resurrecting this glaze was that it is fine at either 6 or 10.

Hmmm, for a clay to be mature from ^04 through to ^10 is impossible. It will be vastly immature at the low end or overfired at the top. Flux levels in the body can't satisfy such extremes in firing. Even bodies claiming to go from ^6 - ^10 is problematic, chances are it will leak at ^6 or bloat / slump / over vitrify and become brittle at ^10. Better to use a midrange clay for 6 and a highfire clay for 10. Are you planning on firing to both 6 and 10 and looking for one glaze to fit both?

14 hours ago, MFP said:

Does that mean we are incorrect about the EPK? 

 

14 hours ago, MFP said:

I don't quite understand the comment about durability....I have a 35 year old piece sitting in my garage with this glaze on it and it looks the same as the day it came out of the kiln.

Screenshot below of what the chemistry would look like for a glaze with 50 colemanite, 50 epk, 15 zircopax plus 2 bentonite. Next to the recipe is a "limits" chart that shows the range (Rge column of the pink box) of each oxide required to produce a durable glaze. Many glazes have figures outside these ranges but they are guidelines. What is really important to look at are the silica and alumina levels. When these are too low the glaze won't wear well and any heavy metals in the glaze have a far greater chance of leaching out of the glaze. Boron is far too high, excess boron makes a "soft" glaze and can actually promote crazing. Another important thing to look at is the R2O : RO flux ratio, it's way off in this recipe, there are no R2O fluxes in this glaze, this will also contribute to a very non-durable glaze.

Hope this helps clarify what some of the concerns are with this glaze. Lots of recipes that are much better than this one.

 

[Pieter Mostert]

Was the unknown ingredient Plastic Vitrox clay? Sounds like it might be this recipe: https://glazy.org/recipes/2875

Be aware that the analysis in glazy uses the theoretical composition of Colemanite (https://glazy.org/materials/15119) whereas what's actually sold may have a different composition, for example https://glazy.org/materials/37220 or https://glazy.org/materials/20787

If the 35 year old piece is functional and has been in use for most of its life, I wouldn't worry about any theoretical durability concerns.

[Denice]

A glaze that looks good at any cone will only be functional at the highest cone.   Fired at C 6 in a electric kiln it wouldn't have any iron spots and would leak fluids through the glaze.  You could put a  C 6 liner glaze inside of a mug or pot to solve this problem.  There has been a lot of changes in glaze formulations in the last 35 years.  These changes are do to many different reasons,  such as gerstley borate  is no longer available not enough left to mine.    You can get some great glazes from the glaze guru's on the forum.  If you are fining oxidation at C6  speckled buff is a great clay that gives your iron spots.    Denice

[MFP]

23 hours ago, Mark C. said:

I think all the spots are from the clay body. Not the glaze.

The glaze looks like any oatmeal glaze of that time on an iron bearing claybody

My honey white is similar . I foire to cone 10 reduction

The huge range of glaze melt from cone 6- to cone 10 is a larger issue . I have no info on that glaze. My honey white does not look good at cone 6 

I use kingman every week but I bought 3,000#s in 1982 from the mine-I'm on my last 400#s now-hopefully it will last until I'm done.\

You should be able to make that glaze with custar feldspar or any potash spar

How about talking to any of your 35 year old potter friends from that era for that reciepe??

You can toggle thru glazy on the web for a look alike. Remember its on a iron bearing clay body .

I have  glaze like that buts its cone 10  only not cone 6.

 

All my old potter friends have forgotten it as well.  It is interesting that they all now act as though having been a professional potter at one time is something they want to forget.  I am wondering if you are right...and the missing 50 is Kingman. We didn't use any other feldspar....so it is quite possible that that is the missing piece. Yes...the spots are from the clay body and very heavy reduction.  We must have worked at the same time. My last fire was in 1983.  Congrats on scoring all that Kingman.....your glazes are probably unique because of it. I am really astounded at the changes in glazing since I last did this....undoubtedly because of the shift to oxidation.....but because I still have a gas kiln, I am not sure that I will switch over completely....old habits die hard.  Thanks for your input.  I would be interested in your white recipe if that is something you want to share. 

[MFP]

7 hours ago, Pieter Mostert said:

Was the unknown ingredient Plastic Vitrox clay? Sounds like it might be this recipe: https://glazy.org/recipes/2875

Be aware that the analysis in glazy uses the theoretical composition of Colemanite (https://glazy.org/materials/15119) whereas what's actually sold may have a different composition, for example https://glazy.org/materials/37220 or https://glazy.org/materials/20787

If the 35 year old piece is functional and has been in use for most of its life, I wouldn't worry about any theoretical durability concerns.

A fellow Kingman user brought to my attention that the missing 50 might be Kingman. Since it was the only feldspar my center used at the time....it would make the most sense that I wouldn't think about writing it down....and the Colemanite was what I had to remember. But since gerstly borate is not longer available it is a moot point.  Thanks very much for your help

[MFP]

9 hours ago, Min said:

Hmmm, for a clay to be mature from ^04 through to ^10 is impossible. It will be vastly immature at the low end or overfired at the top. Flux levels in the body can't satisfy such extremes in firing. Even bodies claiming to go from ^6 - ^10 is problematic, chances are it will leak at ^6 or bloat / slump / over vitrify and become brittle at ^10. Better to use a midrange clay for 6 and a highfire clay for 10. Are you planning on firing to both 6 and 10 and looking for one glaze to fit both?

 

Screenshot below of what the chemistry would look like for a glaze with 50 colemanite, 50 epk, 15 zircopax plus 2 bentonite. Next to the recipe is a "limits" chart that shows the range (Rge column of the pink box) of each oxide required to produce a durable glaze. Many glazes have figures outside these ranges but they are guidelines. What is really important to look at are the silica and alumina levels. When these are too low the glaze won't wear well and any heavy metals in the glaze have a far greater chance of leaching out of the glaze. Boron is far too high, excess boron makes a "soft" glaze and can actually promote crazing. Another important thing to look at is the R2O : RO flux ratio, it's way off in this recipe, there are no R2O fluxes in this glaze, this will also contribute to a very non-durable glaze.

Hope this helps clarify what some of the concerns are with this glaze. Lots of recipes that are much better than this one.

 

I think the missing 50 is Kingman feldspar....since nothing else makes any sense.

[Bill Kielb]

10 hours ago, MFP said:

A fellow Kingman user brought to my attention that the missing 50 might be Kingman. Since it was the only feldspar my center used at the time....it would make the most sense that I wouldn't think about writing it down....and the Colemanite was what I had to remember. But since gerstly borate is not longer available it is a moot point.  Thanks very much for your help

Laguna bought the remaining gerstley borate on site near the mine. The mine was used to supply the borate for nuclear underground test. The pottery community was a very minor fraction user of gerstley. The mine was closed since no more nuclear underground testing. Laguna bought the remaining tons on site and I just have ordered and receive several hundred pounds over the last few months. We still use it in our cone six glazes.

the earth is cone ten, therefore glazes were all cone ten. Gerstley provided a suitable source for boron which is an easy way to make a cone ten glaze melt at cone six. I am not a limits guy but Katz showed the relationship of boron under UMF is relatively linear with respect to cone. 0.15 boron under UMF gets a cone six melt.  0.42 boron under UMF gets a cone 04 melt.

As to clay that melts from cone 04 to cone 10, very questionable especially fully vitrified. As to getting a glaze to do this, I have seen them and in fact there are cone 04 glazes that have tested more durable than cone ten. And there are cone 04 glazes that manage to fire to cone 10. 

as to guessing what this was and how the look was achieved I think a very difficult task. As to durability, without testing its extremely difficult to make any credible statement.

there are far too many unknowns here, I would suggest  a known substitute body and known glaze formulation (cone 10) that produce known fully vitrified durable results. If it’s a cone ten glaze, no need for gerstley anyway.

[liambesaw]

When a shop lists a glaze as 04-10 it usually means 04 bisque 10 glaze.  SPS does that too, it's 04-6 and 04-10 mean bisque at 04, glaze at the high number.  

[Mark C.]

1 hour ago, MFP said:

All my old potter friends have forgotten it as well.  It is interesting that they all now act as though having been a professional potter at one time is something they want to forget.  I am wondering if you are right...and the missing 50 is Kingman. We didn't use any other feldspar....so it is quite possible that that is the missing piece. Yes...the spots are from the clay body and very heavy reduction.  We must have worked at the same time. My last fire was in 1983.  Congrats on scoring all that Kingman.....your glazes are probably unique because of it. I am really astounded at the changes in glazing since I last did this....undoubtedly because of the shift to oxidation.....but because I still have a gas kiln, I am not sure that I will switch over completely....old habits die hard.  Thanks for your input.  I would be interested in your white recipe if that is something you want to share. 

Yes I can share that with you-I'm on a break from production trhis week so it will be am little while-I'm in the beging stages of my last remodel -our bedroom-last room in house that needs some love.I'll check thry my glaze book soon for you-

Any way -i'm still a full time potter and I never want to forget about it-its only been a 45 year career so I have time to reinvent myself and practice Yoga full time someday(kidding about that)

gerstly borate  is still around -I bought a ton when it was rummored it was going away-Laguna still has some -If they rum out I can send you some-I gave two 50# bags away last week.I'm swimming in it. I only use it in a few glazes as its really for melting at lower temps. I never switched to oxidation atmospheres  as I like the unknown nature of different results.Never went to cone 6-gave up raku ,pit firinmg ,dung firing and pinch pots and wet the other way as a porcelain potter making a line of work that folks use everyday for live. Its been a good road to follow with no regrets-The only one is maybe if I could live until 100 I could really figure ceramics out  a little better.

[Bill Kielb]

On 6/1/2019 at 10:45 PM, liambesaw said:

When a shop lists a glaze as 04-10 it usually means 04 bisque 10 glaze.  SPS does that too, it's 04-6 and 04-10 mean bisque at 04, glaze at the high number.  

I think stroke and coat generally performs 04-10 as fully melted. Advertising as you say cone 04 bisque for a glaze would be very confusing in my view. How do they advertise their low fire stuff?

 

[liambesaw]

The lowfire bodies are "06-1"

I asked them about it when I first bought clay and that's just what they told me.  I don't think it applies to glazes and it might just be a local thing

[MFP]

1 hour ago, Mark C. said:

Yes I can share that with you-I'm on a break from production trhis week so it will be am little while-I'm in the beging stages of my last remodel -our bedroom-last room in house that needs some love.I'll check thry my glaze book soon for you-

Any way -i'm still a full time potter and I never want to forget about it-its only been a 45 year career so I have time to reinvent myself and practice Yoga full time someday(kidding about that)

gerstly borate  is still around -I bought a ton when it was rummored it was going away-Laguna still has some -If they rum out I can send you some-I gave two 50# bags away last week.I'm swimming in it. I only use it in a few glazes as its really for melting at lower temps. I never switched to oxidation atmospheres  as I like the unknown nature of different results.Never went to cone 6-gave up raku ,pit firinmg ,dung firing and pinch pots and wet the other way as a porcelain potter making a line of work that folks use everyday for live. Its been a good road to follow with no regrets-The only one is maybe if I could live until 100 I could really figure ceramics out  a little better.

Glad to find someone  on here of the same genre  as myself. I never considered myself an "artist"....I was a "functionalist" and made things that people used. I was a production potter for 10 years....at about the 7 year point, my mother pointed out to me that it was kicking my ass at age 26...so what did I think it was going to be like when I was 40?  I was firing a 20 cubic foot downdraft a week.  I  also have always known that what is going to kill me is my lungs....and pottery is not a good profession for people with lung problems. So I went back to school,  got a PhD and worked in another field for 35 years. I have however been packing a studio around for all those 35 years....at one point I was disgusted with my new occupation and bought the biggest Olympic updraft they made with the intention of resuming pottery.....but then something happened that pointed out to me that I needed to remain at what I was doing. So, ironically, I have a huge gas  kiln that has never been fired. I recently scored an old smaller Olympic cone 10 electric  kiln for bisquing. I can sure see that the change to oxidation really ramped up people's investigating glazing and glaze theory. In looking at stuff on here, I feel like some kind of primitive.....glazing and decorating have become way more sophisticated.  But I must admit that I cringe at the idea of oxidation...but I plan to do a bunch of testing. But somehow, I think I will wind up back with reduction.  Besides...like you...I have a bunch of glazes that haven't been seen in 25 years.  It's not like I am going to be selling again or trying to win art contests....I just want to do some stuff for myself. This revival all started with a young man who does work for me asking to buy the gas kiln.....after questioning him, he clearly had no idea what he was doing...so I told him I would teach him if he helped me set up the studio. 

Yes....I saw that Laguna had some gerstly...so was a bit confused by people saying it was not available.  I know it is a powerful flux which adds more credence to the idea that the other 50 was Kingman. 

It warms my heart to know that you were able to make a living doing pottery  all these years... I loved pottery and was sad to have to leave it. 

Remodeling!! Ack!!  We sold our place on five acres out of town because we couldn't manage it any more....and in the process virtually completely remodeled the inside...then we moved back into our small house we had in town....I never want to remodel anything again!  But good luck...and look forward to hearing from you!

[MFP]

3 hours ago, Bill Kielb said:

Laguna bought the remaining gerstley borate on site near the mine. The mine was used to supply the borate for nuclear underground test. The pottery community was a very minor fraction user of gerstley. The mine was closed since no more nuclear underground testing. Laguna bought the remaining tons on site and I just have ordered and receive several hundred pounds over the last few months. We still use it in our cone six glazes.

the earth is cone ten, therefore glazes were all cone ten. Gerstley provided a suitable source for boron which is an easy way to make a cone ten glaze melt at cone six. I am not a limits guy but Katz showed the relationship of boron under UMF is relatively linear with respect to cone. 0.15 boron under UMF gets a cone six melt.  0.42 boron under UMF gets a cone 04 melt.

As to clay that melts from cone 04 to cone 10, very questionable especially fully vitrified. As to getting a glaze to do this, I have seen them and in fact there are cone 04 glazes that have tested more durable than cone ten. And there are cone 04:glazes that manage to fire to cone 10. 

as to guessing what this was and how the look was achieved I think a very difficult task. As to durability, without testing its extremely difficult to make any credible statement.

there are far too many unknowns here, I would suggest  a known substitute body and known glaze formulation (cone 10) that produce known fully vitrified durable results. If it’s a cone ten glaze, no need for gerstley anyway.

Yes....I have seen that Laguna has gerstly. I bought a small amount of this clay body from a local vendor. It is made by a professional clay company.  The 04 is for raku...and sounds like what we used to do with our cone 10 body....that the raku was one step above bisque. They were clear that the body is still open at 6 and does not vitrify til 10.   I am teaching someone to throw and this was the only white body around here with grog in it. It's much easier for a person to learn with a stouter body. I only bought 200 pounds of it...so if it turns out to be crap...no problemo.  Since I know virtually nothing about these new white bodies, some experimenting is inevitable.  I just know I don't like throwing with cream cheese. 

[MFP]

13 hours ago, Min said:

Hmmm, for a clay to be mature from ^04 through to ^10 is impossible. It will be vastly immature at the low end or overfired at the top. Flux levels in the body can't satisfy such extremes in firing. Even bodies claiming to go from ^6 - ^10 is problematic, chances are it will leak at ^6 or bloat / slump / over vitrify and become brittle at ^10. Better to use a midrange clay for 6 and a highfire clay for 10. Are you planning on firing to both 6 and 10 and looking for one glaze to fit both?

 

Screenshot below of what the chemistry would look like for a glaze with 50 colemanite, 50 epk, 15 zircopax plus 2 bentonite. Next to the recipe is a "limits" chart that shows the range (Rge column of the pink box) of each oxide required to produce a durable glaze. Many glazes have figures outside these ranges but they are guidelines. What is really important to look at are the silica and alumina levels. When these are too low the glaze won't wear well and any heavy metals in the glaze have a far greater chance of leaching out of the glaze. Boron is far too high, excess boron makes a "soft" glaze and can actually promote crazing. Another important thing to look at is the R2O : RO flux ratio, it's way off in this recipe, there are no R2O fluxes in this glaze, this will also contribute to a very non-durable glaze.

Hope this helps clarify what some of the concerns are with this glaze. Lots of recipes that are much better than this one.

 

They do not claim that the body matures for that whole range. It is for raku at 04, still open at 6 and vitrifies at 10

[MFP]

3 hours ago, MFP said:

A fellow Kingman user brought to my attention that the missing 50 might be Kingman. Since it was the only feldspar my center used at the time....it would make the most sense that I wouldn't think about writing it down....and the Colemanite was what I had to remember. But since gerstly borate is not longer available it is a moot point.  Thanks very much for your help

Hmm...plastic vitrox? Is there another name for it? I think not as I do not recall  that material.  I cannot remember if I ever used it for anything. You guys on here are so sophisticated compared to the time I worked.  We were "make do with what you have" potters....and the simpler the better.  Glaze theory was only done at universities.  And everything was a big secret!

[Pieter Mostert]

1 hour ago, MFP said:

Hmm...plastic vitrox? Is there another name for it? I think not as I do not recall  that material.  I cannot remember if I ever used it for anything. You guys on here are so sophisticated compared to the time I worked.  We were "make do with what you have" potters....and the simpler the better.  Glaze theory was only done at universities.  And everything was a big secret!

PV clay? https://digitalfire.com/4sight/material/pv_clay_1152.html

[MFP]

On 6/1/2019 at 9:58 AM, Min said:

Hmmm, for a clay to be mature from ^04 through to ^10 is impossible. It will be vastly immature at the low end or overfired at the top. Flux levels in the body can't satisfy such extremes in firing. Even bodies claiming to go from ^6 - ^10 is problematic, chances are it will leak at ^6 or bloat / slump / over vitrify and become brittle at ^10. Better to use a midrange clay for 6 and a highfire clay for 10. Are you planning on firing to both 6 and 10 and looking for one glaze to fit both?

 

Screenshot below of what the chemistry would look like for a glaze with 50 colemanite, 50 epk, 15 zircopax plus 2 bentonite. Next to the recipe is a "limits" chart that shows the range (Rge column of the pink box) of each oxide required to produce a durable glaze. Many glazes have figures outside these ranges but they are guidelines. What is really important to look at are the silica and alumina levels. When these are too low the glaze won't wear well and any heavy metals in the glaze have a far greater chance of leaching out of the glaze. Boron is far too high, excess boron makes a "soft" glaze and can actually promote crazing. Another important thing to look at is the R2O : RO flux ratio, it's way off in this recipe, there are no R2O fluxes in this glaze, this will also contribute to a very non-durable glaze.

Hope this helps clarify what some of the concerns are with this glaze. Lots of recipes that are much better than this one.

 

Then the missing 50 is not EPK.  The properties everyone keeps describing on here are not present in this glaze.  It is not fussy in any way.....doesn't run, matures everywhere in the kiln just fine, does not craze and is durable   So EPK is incorrect.