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Nicky S

Hardening of glaze

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53 minutes ago, C.Banks said:

I've heard a good rule of thumb is up to 2% bentonite. 2 parts sounds like a lot of bentonite.

I meant as part of the recipe.  Some people say percent but that's a misnomer because recipes don't often add up to 100%.  If you use the word part instead it makes sense.

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5 hours ago, liambesaw said:

I meant as part of the recipe.  Some people say percent but that's a misnomer because recipes don't often add up to 100%.  If you use the word part instead it makes sense.

true enough - I sometimes interchange grams and percent and just assume 100g gram batches

In a 100g batch 2g of bentonite is a good rule of thumb.

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11 hours ago, Babs said:

So if yoyr recipe doesn't add to100 you'll gave to change it to percentage anyway for your 100g batch........

Just saying....:-)/)

Thanks Babs, Could you just explain why I should  please? because I have a bunch of recipes that work well off this base recipe.  Cheers G

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Well how do you easily make a 100gm batch from your base recipe which adds up to under 100 as stands?

If adding 2% to you base...makes difficultish maths

Gerts bor 35from Your recipe  Expressed as % 36.08

Do this for each ingredient and your additionof  2% Bentonite is 2gms.

But I am with Min. Seems s.thing left out of recipe to be written as is....almost addi g up to 100i.e. someone has already expressed these ingredients as a percentage and 5 out from 100 this ingredient missing..

Could go old school and if small batch a pinch or tspoon but record how much bentonite is added..

Easier and prob more effective to sieve and heat

 

 

 

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Grace:

there is a very simple fix to your recipe to bring it from 95 to 100%, that will also help fix the low alumina issue without altering the finish. 

Keep your 95% recipe and add 5% grolleg kaolin. Grolleg is very clean clay, plus it will supply 37% alumina! plus it will help a bit with suspension. Do you have access to calcium bentonite? ( also known as Fullers earth)

T

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1 hour ago, glazenerd said:

Grace:

there is a very simple fix to your recipe to bring it from 95 to 100%, that will also help fix the low alumina issue without altering the finish. 

Keep your 95% recipe and add 5% grolleg kaolin. Grolleg is very clean clay, plus it will supply 37% alumina! plus it will help a bit with suspension. Do you have access to calcium bentonite? ( also known as Fullers earth)

T

Alright, here is my opinion and the whys

  • Normalizing this to 100% really does not change much (See 100% batch column)
  • This glaze lacks 10% or more clay so it is unlikely to stay suspended (5.26% EPK)
  • Boron levels at .45 make this an 04 glaze. Not sure if that is what it is supposed to be or did someone add Gerstley until they sort of melted the giant amount of silica (Sort of)
  • The chemistry in Stull is poor and shows underfired (Not good)
  • The high R20 indicates it is not durable. (Very high early melt)
  • 44% silica is extremely high
  • .11 Effective Alumina is low (Very low)
  • Lithium Carb is water soluble which adds more difficulty to the whole thing

 

The basic chemistry says: Not durable, hard to tell where it fires, artistic only and likely difficult to keep in suspension.

If the desired surface and firing temperature is known I would just mix up a durable formulation to the look I wanted instead of this unless this yields some fantastic unreproducible result.

Its hard for me to find anything redeeming about this recipe. Just my opinion and basis for though.

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23 hours ago, C.Banks said:

true enough - I sometimes interchange grams and percent and just assume 100g gram batches

In a 100g batch 2g of bentonite is a good rule of thumb.

Two percent  is generally the maximum

Edited by Bill Kielb

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2 hours ago, glazenerd said:

Grace:

there is a very simple fix to your recipe to bring it from 95 to 100%, that will also help fix the low alumina issue without altering the finish. 

Keep your 95% recipe and add 5% grolleg kaolin. Grolleg is very clean clay, plus it will supply 37% alumina! plus it will help a bit with suspension. Do you have access to calcium bentonite? ( also known as Fullers earth)

T

Tom is this Fullers earth from the UK . I know its sold as a beauty product on amazon as well. Where you getting yours??

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@neilestrick

Apparently at almost 37% Gerstley, that is not working right now. See analysis above, this glaze has lots of issues. Gerstley is not a great suspender, bentonite much more traditional up to 2% maximum

Edited by Bill Kielb

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@Grace london has said she is using the above glaze for sculpture not functional wares and the issue she was having was crystals forming in the slurry, not suspension issues. Agreed it definitely would not pass muster for a durable glaze on functional wares but that isn't what Grace is using it for.

@Grace london, it's standard practice to have a base recipe add up to 100. Additions like opacifiers or colourants or suspending agents get added as additions on top of the 100. Having 100 as a base makes it easier to add additions of colourants, opacifiers or suspending agents. It also makes it easier to compare recipes if the standard 100 is used, especially if you are not using glaze calc software. There are times when a colourant or opacifier or suspending material needs to be included in the 100 though. Example would be yellow ochre. It contains iron but it also contains clay, if there is a lot of it a recipe it could be included in the 100.  If your recipe is working for you, and you aren't having shivering issues from all the lithium in it, to make the math add up to 100 your glaze recipe would be:

Gerstley Borate              36.80

 Nepheline Syenite         5.30

 EP Kaolin                            5.30

 Flint                                       44.20

 Lithium Carbonate         8.40

total                                       100.00

 

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8 minutes ago, Min said:

@Grace london has said she is using the above glaze for sculpture not functional wares and the issue she was having was crystals forming in the slurry, not suspension issues. Agreed it definitely would not pass muster for a durable glaze on functional wares but that isn't what Grace is using it for.

@Grace london, it's standard practice to have a base recipe add up to 100. Additions like opacifiers or colourants or suspending agents get added as additions on top of the 100. Having 100 as a base makes it easier to add additions of colourants, opacifiers or suspending agents. It also makes it easier to compare recipes if the standard 100 is used, especially if you are not using glaze calc software. There are times when a colourant or opacifier or suspending material needs to be included in the 100 though. Example would be yellow ochre. It contains iron but it also contains clay, if there is a lot of it a recipe it could be included in the 100.  If your recipe is working for you, and you aren't having shivering issues from all the lithium in it, to make the math add up to 100 your glaze recipe would be:

Gerstley Borate              36.80

 Nepheline Syenite         5.30

 EP Kaolin                            5.30

 Flint                                       44.20

 Lithium Carbonate         8.40

total                                       100.00

 

Exactly!

So buy sieve and  little immersion heater thingie if continuing with your glaze as is

 

Edited by Babs

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18 minutes ago, Min said:

@Grace london has said she is using the above glaze for sculpture not functional wares and the issue she was having was crystals forming in the slurry, not suspension issues. Agreed it definitely would not pass muster for a durable glaze on functional wares but that isn't what Grace is using it for.

@Grace london, it's standard practice to have a base recipe add up to 100. Additions like opacifiers or colourants or suspending agents get added as additions on top of the 100. Having 100 as a base makes it easier to add additions of colourants, opacifiers or suspending agents. It also makes it easier to compare recipes if the standard 100 is used, especially if you are not using glaze calc software. There are times when a colourant or opacifier or suspending material needs to be included in the 100 though. Example would be yellow ochre. It contains iron but it also contains clay, if there is a lot of it a recipe it could be included in the 100.  If your recipe is working for you, and you aren't having shivering issues from all the lithium in it, to make the math add up to 100 your glaze recipe would be:

Gerstley Borate              36.80

 Nepheline Syenite         5.30

 EP Kaolin                            5.30

 Flint                                       44.20

 Lithium Carbonate         8.40

total                                       100.00

 

My advice, unless this gives spectacular results just mix up a proper lithium matte for cone 04. It likely will save natural resources and perform  consistently. Certainly can be durable as well so unless this is extra special I would replace it. The 100 gram issue is minor and I have posted the normalized one to the 100 th gram already so just use the 100% batch column on the spreadsheet if that is the issue.

Edited by Bill Kielb

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1 hour ago, Bill Kielb said:

@Mark C.

molten earth?

Magma is a brand of  a suspension agent. It works like nothing else I have ever used . Been using it in just a few real settling hard glazes for 20 plus years now . Well worth it. Yes I have a few glazes that use 2% bentonite but when you really need suspension-this stuff is the best.

Lest say you have to float a brick in water well this is the sytuff that can make that happen. A little dab will do ya as thay say.

You can find it online at a few shops as its not well known.One small bag will last your lifetime unless you are building a sailboat from bricks and need to thicken the whole pond.

Here it is known as an anti gravity multipurpose additive

When ever I feel the need for some anti gravity magic I always go for the Magma-feeling a bit held down to earth -well just a nip of Magma and you are floating sky high again

http://www.brackers.com/magma-miracle-anti-gravity-multipurpose-additive/

Edited by Mark C.

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Mark:

in small batches: you almost have to buy calcium bentonite online. My supplier is minimum of 50lbs, they prefer 500 lb orders. PM if you are interested.

Bill: Grace likes her recipe and has adapted it for her use, so my reply was to keep it that way.

T

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2 hours ago, Bill Kielb said:

@neilestrick

Apparently at almost 37% Gerstley, that is not working right now. See analysis above, this glaze has lots of issues. Gerstley is not a great suspender, bentonite much more traditional up to 2% maximum

I was only referring to the suspension. I agree that it has other problems. The OP had suspension issues, not Grace.

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2 hours ago, neilestrick said:

The Gerstley will help keep it suspended. However if you use a Gerstley substitute it'll have problems.

@neilestrick

understood my point was in reference to bentonite really being a suspender not Gerstley

Edited by Bill Kielb

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14 minutes ago, Bill Kielb said:

@neilestrick

understood my point was in reference to bentonite really being a suspender not Gerstley

From Digitalfire: Gerstley Borate is also very plastic and thus suspends and hardens glazes as they dry. In fact, few clays have the plasticity and the ability to retain water that GB has. A GB slurry can take many hours to dewater on a plaster batt, even in a very think layer. Thus it is common to find Gerstley Borate based recipes having no clay content. 

I'm not suggesting that Gerstley should be added to anything as a suspender, because it would obviously have other effects on the glaze, but at 35% it will definitely have suspension qualities, and therefore the 5% EPK in the glaze probably isn't an issue.

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