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Rockhopper

Glaze From Local Creek Clay - What To Add ?

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A couple of years ago, I was trying to develop a workable ^6 clay body, starting with clay I dug from a nearby creek, and several forum members contributed valuable suggestions to that project.  After a lot of trial and (mostly) error, including a couple that completely melted in the kiln, I was able to make a few flower pots that now hold plants in my office - but never really found a blend that was 'friendly' to work with, and wound up setting the buckets aside to pursue other things.

 

I now have some time to re-visit my creek clay - and decided to take a different approach:  I want to see if I can develop it into a glaze.

 

As a starting point, I made some slip, and applied a coating to the inside of a small bowl - and fired at ^5-ish.  (^6 on the sitter gives me a near perfect bend on a #5 self-supporting cone, with slight bending on a 6.)

 

The result is a light cream/butter color, but with the texture of 200-grit sandpaper.  And, as could probably be predicted by the texture, is very porous.  Obviously not something I can use on a mug or bowl that's going to be handled.

 

So...  I'm once again reaching out to those that have been down this road before me, and asking for suggestions: 

 

What would you add, and in what proportions, to turn this into a "glassier" glaze.  (I wouldn't mind if it winds up being a matte finish - but I need to get it smoother, and less absorbent than the clay it's applied to.)

 

post-19205-0-72241100-1482975963_thumb.jpg

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Clay bodies typically run in the 2.80 to 3.25 total alkali (molar) for stoneware and 3.50 up to 4.25 total alkali (molar) for porcelain. Given the butter/cream color; suspect there is a high percentage of titanium, with a far less amount of iron in this clay. To get it to a glassy state, you would need to raise the total alkali into the 9.00 total alkali (molar) range. Total alkali = potassium and sodium. Calcium, magnesium, and lithium can also be used: in which case total fluxes should run in the 19-20 range (molar).

 

As a simple base line; start with: 25% native clay, 20% silica, and 55% Nep SY.  (8.58 total alkali - molar)

 

Nerd

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The color is very nice. You could use Nerd's suggestion but do a test in increments of 5% of the silica and Neph Sy.

Begin with 5 silica and 10 NS and increase. You may have to test again to get the right ratio, Texture is determine by the ratio between the silica and the clay.

Marcia

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You should take a look at the  Ian Currie approach to Glaze Research  http://ian.currie.to

The idea is to make a grid with clay, silica, and "flux materials" and in a single firing  to get quickly to a region where tweaking with line blends will more useful. 

 

There have been some discussions on CAD on this topic.  Search for "Currie Grid"

 

Ian published two books on the subject.  They are out of print but may be available at your library. 

The citation information is on his website.

 

LT

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Making clay or glaze from local materials requires lots and lots and lots of testing

 

No doubts about that Mark...

 

I spent over a year, trying various combinations of EPK, OM4, Feldspar, and Flint, added to my base clay, trying to get a 'wheel-friendly' body. (Didn't have my own kiln, so would mix several small batches, make some test pieces, then wait a week or two for the studio owner to fit them into a firing.)  I learned a lot about clay in the process - but when I reached the point where "my" clay was no longer the primary ingredient, I felt like I was just adding some of my clay to 'other stuff', and gave up.  (In my mind, it was OK to add stuff to my clay to make it work ... but when it was the other way around, the end result was no longer the clay from 'my creek'.)

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As a simple base line; start with: 25% native clay, 20% silica, and 55% Nep SY.  (8.58 total alkali - molar)

 

Nerd

 

 

The color is very nice. You could use Nerd's suggestion but do a test in increments of 5% of the silica and Neph Sy.

Begin with 5 silica and 10 NS and increase. You may have to test again to get the right ratio, Texture is determine by the ratio between the silica and the clay.

Marcia

 

The best answer is probably "try it and see"... but would doing the same with Custer Feldspar, instead of NS, be an option worth trying ?  (I already have some Custer on-hand, and would have to go buy some NS to try it.)

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Back in collage in clay and glaze classes I made local clay work at cone 10 for a project in that class-I did end up as you said with mostly other new materials to make the local clay work.

Thats the deal with most local clays most are not suitable for pottery making except pit firing and pinch pots. 

So adding some of your local clay as you found out is not really doing much with it. I have not done any local clay work since this experiment in class in 1973.

If you want a pure experience fire it to 1200 degrees in a pit fire. Making it work at higher temps just makes it a minor addition to materials that can take the heat.

Most local clays are very low temp. as you have discovered. They bloat and come apart pretty easy without major additions. 

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The color is very nice. You could use Nerd's suggestion but do a test in increments of 5% of the silica and Neph Sy.

Begin with 5 silica and 10 NS and increase. You may have to test again to get the right ratio, Texture is determine by the ratio between the silica and the clay.

Marcia

 

Marcia -  When you say 'begin with 5 silica and 10 NS' - are those numbers ( a ) percentages of the total, or ( b ) percentages to add ?  From what I've read elsewhere about glazes, I'm guessing it's ( a ), since ( b )would make it approx 4% silica and 8% NS - but thought I should ask, just to be sure.

 

Examples:

a )  85g clay + 5g silica + 10g NS = 100g total

 

b ) 100g clay + 5g silica + 10g NS = 115g total

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Custer can certainly be used.

 

 

I want to see if I can develop it into a glaze.

My recommendations were based on your comment.

 

 

I spent over a year, trying various combinations of EPK, OM4, Feldspar, and Flint,

You need a higher plasticity clay: other than what you have used. I would try FHC (Foundry Hills Creme), Plastic Vitrox (PV clay), or additions of bentonite (small percentages.)

Nerd

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As a starting point, I made some slip, and applied a coating to the inside of a small bowl - and fired at ^5-ish.  (^6 on the sitter gives me a near perfect bend on a #5 self-supporting cone, with slight bending on a 6.)

 

The result is a light cream/butter color, but with the texture of 200-grit sandpaper. 

 

attachicon.gif20161228_203518b.jpg

Like clay, glaze can have too much silica and not enough flux. I am betting that sandpaper feel is too much silica for the amount of flux. Have you sieved your clay? Is it actually clay or is it silt? Most native clay I have dealt with has too much sand (silica), and this sand is in particle sizes too large to melt down in a normal firing. Hence the sandpaper finish.

 

 

If your "clay" has too little clay (ie, kaolinite, meaning actual clay particles) then you will struggle to get it to work as a clay, either in glaze recipes or clay recipes.

 

When you put some slip of this clay on a plaster bat, how fast does the water leave it? If it leaves fast, then it is silt.

 

If you can, and if you can be bothered, the best thing is to get it tested in a lab to see what the chemical makeup is.

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Custer can certainly be used.

 

 

I want to see if I can develop it into a glaze.

My recommendations were based on your comment.

 

 

I spent over a year, trying various combinations of EPK, OM4, Feldspar, and Flint,

You need a higher plasticity clay: other than what you have used. I would try FHC (Foundry Hills Creme), Plastic Vitrox (PV clay), or additions of bentonite (small percentages.)

Nerd

 

Thanks Nerd.  Your input is appreciated - I am definitely aiming for a glaze this time around.  My comment about trying various combinations was in response to Mark's post that local clays require "lots and lots of testing".  Not sure if FHC or PV are available locally, but will keep those in mind if I decide to make another attempt at a clay body.

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Like clay, glaze can have too much silica and not enough flux. I am betting that sandpaper feel is too much silica for the amount of flux. Have you sieved your clay? Is it actually clay or is it silt? Most native clay I have dealt with has too much sand (silica), and this sand is in particle sizes too large to melt down in a normal firing. Hence the sandpaper finish.

 

If your "clay" has too little clay (ie, kaolinite, meaning actual clay particles) then you will struggle to get it to work as a clay, either in glaze recipes or clay recipes.

 

When you put some slip of this clay on a plaster bat, how fast does the water leave it? If it leaves fast, then it is silt.

 

If you can, and if you can be bothered, the best thing is to get it tested in a lab to see what the chemical makeup is.

 

 

Definitely lots of sand before sieving.  My first attempt to throw with it was like grabbing hold of a drum-sander.

 

It's been sieved several times - starting with 1/4" hardware cloth to remove the 'big stuff', then some window screen (16 mesh), a nylon paint-strainer bag, and finally, with an 80 mesh - .0055 - screen.

 

Poured some onto plaster, along side some casting slip and some Standard #112 - it dried faster than the casting slip, but about the same as the #112. (Can't say for sure I had same water percentage in each to start with - just eyeballed the consistency.)

 

Would actually like to have it lab analyzed (if I can afford it) - but have no idea where to go for that.  I've looked a little bit, and so-far the labs I've found do soil testing for agricultural purposes (pH, etc.) - or they'll test for presence of lead or other toxins - but don't do actual content breakdown.

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Have you tried firing some of it on its own in a little bowl? Does it vitrify?

 

Sounds like it has too much silica as it, wouldn't add any more. Just add flux (potash spar, neph syenite, whatever you want) in a line blend to see when it starts to vitrify.

 

However , if it does not have enough actual kaolinite, it may still be sandpaper textured even to when you are down to just 20% creek clay. All flux and silica and no clay = sandpaper.

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This is how I extract clay from the sandy dried mud from my pond:


A quick way to extract the sandy bits from the clay bits:

First crush the stuff until it will pass through a window screen. 

Next, add water to this and make a thin slurry.  Do this with a small amount at a time, say a couple of liters of water. Using a clear container makes it easier to see when the gritty bits have separated.

Using a paint mixer, stir until all particles are suspended. When the stirring stops, the heavy bits will sink quickly.  As soon as the sediment builds up, pour off the suspended slurry.  The sediment will be almost all non-clay particles.  Set this aside as Silica/Rocks.

The slurry that is poured off is now more concentrated in clay that the original slurry.  Feel it with you hand and if it is still 'gritty' then you can do the stir, settle, pour sequence again.  Each time you through the cycle, the slurry becomes less gritty and more clayie.  The particle size of the suspended slurry will become finer.   

Let the slurry dry by evaporation, or you can boil away some of the water. 

When dry, crush it into a fine powder and use as the Clay ingredient in a glaze.  Or use it as Clay in a decorative slip to be painted over leather hard or bone dry ware. 

This process is similar to the process for making Terra-Sig (TS), except it does not have any deflocculant added.  The TS process is trying to get rid of all but the finest particles.  The process I am using is to get read of the heaviest particles without losing any of the clay particles.  Clay particles are lighter (less dense) than silica and rock particles. Adding deflocculant is unnecessary and if used also removes the larger clay particles.  The process is quite similar to the riffle techniques used by the Chinese and Korean potters 500+ years ago, and by miners panning for gold.

 

LT

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On 12/29/2016 at 11:02 AM, Mark C. said:

Making clay or glaze from local materials requires lots and lots and lots of testing

I'd like to know if the clay I dug from a very Rocky local Indiana creek is pure kaolin clay. Its a solid gray in color, and after storing it for a year, it didn't even mold. Other light brown colored clay from the same creek had molded. I know moldy clay after aging improves elasticity. This gray clay looks and feels like pure clay of some sort. I know this clay came directly from the source ( huge rocks , nothing but rocks. Would it be a porcelain clay body?

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A 'clay body' is a blend of clays and other ingredients that make a workable mix. Porcelain,  for example, is kaolin, feldspar, and silica. What you're dealing with is just a single clay. Personally, I couldn't even venture a guess as to what it is without actually touching it.  Have you processed the clay?

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On 12/28/2016 at 8:57 PM, Rockhopper said:

A couple of years ago, I was trying to develop a workable ^6 clay body, starting with clay I dug from a nearby creek, and several forum members contributed valuable suggestions to that project.  After a lot of trial and (mostly) error, including a couple that completely melted in the kiln, I was able to make a few flower pots that now hold plants in my office - but never really found a blend that was 'friendly' to work with, and wound up setting the buckets aside to pursue other things.

 

I now have some time to re-visit my creek clay - and decided to take a different approach:  I want to see if I can develop it into a glaze.

 

As a starting point, I made some slip, and applied a coating to the inside of a small bowl - and fired at ^5-ish.  (^6 on the sitter gives me a near perfect bend on a #5 self-supporting cone, with slight bending on a 6.)

 

The result is a light cream/butter color, but with the texture of 200-grit sandpaper.  And, as could probably be predicted by the texture, is very porous.  Obviously not something I can use on a mug or bowl that's going to be handled.

 

So...  I'm once again reaching out to those that have been down this road before me, and asking for suggestions: 

 

What would you add, and in what proportions, to turn this into a "glassier" glaze.  (I wouldn't mind if it winds up being a matte finish - but I need to get it smoother, and less absorbent than the clay it's applied to.)

 

post-19205-0-72241100-1482975963_thumb.jpg

add ball clay. Or use slip then polish, a lot of work. Ive found high quality clay in rocky creek beds, but had to run it through 80 mesh screen. Liquify the clay of course. I dig my clay wet, let it get bone dry, crush it down to a powder, screen it with 80 mesh. Add water to it till its thin. Then run it through 80 mesh screen again. use your kidney shaped smoothing tool on your pottery when just leather hard. Dip it in water often for a really smooth finish

Edited by chopper
add on

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