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What additions to stiffen ash glazes

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I've been making ash from a number of sources over the past months and found a few local sources of volcanic ash. So I started testing and had some awesome results with pearlescent blues and pinks. Pretty stoked :)

I'm using a matte clear glaze base that works well in both of my main kilns (gas and electric). I'm using a straight 10% addition of ash as my starting point without any changes to the base.  Thought being that if I get anything cool from I'll progress it.

The results are usually very runny, especially with wood ash and vegetation ash, so wanted to ask how do I start to compensate for this, knowing that each ash will have a different composition?

I have no chemistry background but learning fast and really after some understanding as to where I start that process. I have a basic grasp of glaze composition and my instinct tells me to up the alumina and reduce the Silica but I couldn't back that up with any sound reasoning haha. I just joined up with Insight and will start some tutorials this week and thought this would be a good starting point.

From other discussions I know I can replace feldspars with volcanic ash and that's worked well but i've not had runny issues with the volcanic ash.  Not yet anyway, touch wood.

 

VC72 Base glaze ( from John Britts mid fire) fired to cone 6 in either gas or electric:

24 Nepheline syenite

40 Silica

4 whiting

7 Kaolin

11 dolomite

12 Gerstly borate 

2 zinc oxide

2 bentonite

 

The finished glaze is very smooth and glassy so presume the ashes are high in Silica? 

Cheers,

Liam

 

 

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The typical rivulet/spiderweb-type ash glazes are high in calcium but low in silica. As you increase silica they start to smooth out, and don't rivulet/spiderweb. They are runny by nature. As they become less runny, they web less. So there's only so much you can do to limit the running if you want to maintain that look. If you're not going for the rivulet look, then you can simply increase the EPK and silica in equal parts to stiffen it up.

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Hey Neil, they don't have a riverlet look really, they are pretty smooth and very glossy for a matte base glaze, I'll try with additions of Kaolin in 5% increments in my next firing.

I'll see if I can add a photo from my phone too

Thanks for the advice!

 

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Not the best photo sorry, but you can see the glaze is quite smooth and glossy without the riverlets.   I think i prefer it this way so will try with the kaolin, thanks for that and your tips on my previous post Neil.  This is 10% wood ash from our fireplace and I really liked the translucent blue where it's pooled.  I have more wood ash than any of the other ashes so maybe I'll run all my initial tests with this so I can get a feel for it.  Kaolin testing here I come!

Also decided to stop testing on sake cup forms and use small bowls to save my shelves... Simple idea you'd think but didn't come to me in time... ah well :)

 

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Am I seeing some crazing in your image? Looks like there are fine cracks running in the glaze, if for functional ware, I would be a little concerned. Maybe a change in your cooling cycle would be needed. Either that or adjust the COE for the clay body.

 

best,

Pres

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Hey Pres, yes a few crackles in this firing as I smashed my thermocouple so finished without much control.  Thankfully the new one arrived today so hopefully all good for the next one if I can suss the Tonky auto tune...

They are little sake cup forms but not for use or leaving the property, our thoughts were to just practice clean cylinder forms and either make a sizable wall installation of colourful pot shapes from them  or they have a date with a .22 round and drainage material under the vege garden :)

Lots of testing atm with plenty of fails but we have grand plans for the vege gardens and a good eye with the .22!

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Hey Pretta, 

This firing was to cone 6 in an electric kiln.  I have a few gas kilns too but they are out of action for a week while I refit them.

Three of the kilns can fire cone 10 easily.  Currently I'm looking at the cone 6 glazes I've made, as they are firing really well in both kiln types.  Especially when I have a functioning thermocouple and the correct pyrometric cone in the kiln.  06 pyrometric cones melt at cone 6 btw, probably not worth a news flash but did remind me to put my glasses on next time haha 

I'm looking to get a better understanding of the chemistry of the glaze ingredients and how they interact, cone 6 is good for this with a solid base glaze to work with as it's pretty economic.  Especially with my latest gas kiln.

 

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Alumina hydrate has been used by crystaline glazers for decades to control glaze run. Crystalline glaze is more fluid than your example. Adding NZ kaolin would certainly help. However, alumina hydrate from 1/4 to maximum of 1% will stop it cold in its tracks. 

T

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The way to learn about ash glaze formulation is to take your ash and conduct a triaxial blend with ash at one corner, clay at another corner, and flint at the third corner.  

The Currie method is a well designed technique based on the triaxial blending idea.  There are two books and several CAD forum threads on the procedure.  An internet search for Ian Currie pottery will get you started. 

If all you are trying to do is to increase the "stiffness" of an existing recipe, I recommend conducting a line blend with the recipe and EPK. Or instead of EPK use the clay body itself as a part of the glaze recipe.  Again conduct a line blend recipe and clay body; that is essentially the way glaze is formed on wood fired ware that starts with no glaze applied. 

LT
 

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Another approach instead of adding kaolin is to remove some of the fluxes you have in your glaze.   Both the crazing and the runniness evident in your picture strongly suggest (to me anyway) that your glaze has way too much flux in it.  

I might look at reducing or removing the gerstley borate as a start.  You will probably lose some of that baby-blue borate flush evident at the bottom of your test piece, bu since borate is such a low temperature melter it will probably go a long way to reducing the runniess.

just a thought.

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Thank you for the responses and tips, thermocouple is now replaced and Friday afternoon is here! Time to put it to practice :)

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Sorry “newbie” question here.

You can work with ashes in ^6 glazes?  Not soda ash.  I tried soda ash just sprinkled on top of glaze and it came out rough.  Not melted but underfired.  

I thought with right fluxes you can play with ash in ^10 Firing.  

Depending on when the wood and type of tree harvested I know how ash affects the outcome.  I only have knowledge with ash glazes in woodfire. I’ve looked at 3 schools ^6 glaze glaze recipe but found no tree ash as an ingredient.  One fired mainly electric, another mostly gas and the other - a 4 year college fired all kinds. 

Does that mean I can experiment with ash? I have some oak and pine that I washed and screened a while back.  

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8 hours ago, preeta said:

Sorry “newbie” question here.

You can work with ashes in ^6 glazes?  Not soda ash.  I tried soda ash just sprinkled on top of glaze and it came out rough.  Not melted but underfired.  

I thought with right fluxes you can play with ash in ^10 Firing.  

Depending on when the wood and type of tree harvested I know how ash affects the outcome.  I only have knowledge with ash glazes in woodfire. I’ve looked at 3 schools ^6 glaze glaze recipe but found no tree ash as an ingredient.  One fired mainly electric, another mostly gas and the other - a 4 year college fired all kinds. 

Does that mean I can experiment with ash? I have some oak and pine that I washed and screened a while back.  

Wood ash is primarily calcium, a flux used in a large percentage of glazes. So yes, it will work at cone 6 as a flux. It does not work all that well sprinkled on top of glazes like it does at cone 10, though.

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On 8/3/2018 at 4:48 AM, Magnolia Mud Research said:


The way to learn about ash glaze formulation is to take your ash and conduct a triaxial blend with ash at one corner, clay at another corner, and flint at the third corner.  

The Currie method is a well designed technique based on the triaxial blending idea.  There are two books and several CAD forum threads on the procedure.  An internet search for Ian Currie pottery will get you started. 

If all you are trying to do is to increase the "stiffness" of an existing recipe, I recommend conducting a line blend with the recipe and EPK. Or instead of EPK use the clay body itself as a part of the glaze recipe.  Again conduct a line blend recipe and clay body; that is essentially the way glaze is formed on wood fired ware that starts with no glaze applied. 

LT
 

This is just what I was looking for thanks Magnolia - not that I knew what I was looking for when I posted of course...  instead of adding new ingredients into a very good base and looking to fix the results I should be looking at the new materials and moving forward from there.

Great method for testing and fairly straight forward, just need to work out how to do it in the space I have and sort out volumes.  I have a variety of ashes plus a few locally dug clays, so only have to source a flint/Silica. That will probably be store bought but there is a New Zealand source a few hours away, might be a fun trip.  Enough to keep me out of trouble for a couple of months I reckon.

I've applied some of the other approaches mentioned above to my current glaze mixes, hopefully these will open my eyes to some of their mysterious chemistry but the triaxial method allows me to fully explore each new material which is awesome :)

 

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