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washed or unwashed wood ash


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#1 buckeye

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Posted 21 December 2011 - 10:14 PM

So I have a bunch of wood ash saved up and I wa nt to make this glaze ash glaze but it calls for Unwashed ash. Everything I have read it sounds like it is safer and better using washed ash. My biggest concern after reading Phil Rogers book "ash glazes" is mixing up a batch of glaze with unwashed ash and it not being usuable within days or weeks. I would really like to be able to mix up a big batch and not having to worry about it being unusable in days or a few short weeks.

I am hoping someone has worked with wood ash who might be able to tell me how much is using washed ash going to change the out come of this glaze? Can I use washed ash and supplement the soluble alkali that I removed from washing with something else that will give me the same effect or close?

#2 bciskepottery

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Posted 21 December 2011 - 10:42 PM

Take a look at today's Ceramic Arts Daily feature with Mark Issenberg; its on using fireplace ashes for glazes:

"To begin, prepare ashes by running them through a flour sifter to remove unburned wood, charcoal and big chunks of debris, then run the dry ash through a 40-mesh screen. I usually process a 5-gallon bucket of ash at one time. "Caution: Wood ash is caustic, so work in a well-ventilated area with a respirator, and wear safety goggles and chemical resistant gloves.

"The next step is to weigh equal amounts of ash and Redart clay. I only mix up what I’ll use in one firing (1000 grams of each) since the ash glaze does not store well. After mixing with water, run the glaze through a 40-mesh screen then through an 80-mesh screen to get it to the right consistency for spraying. Use a thinner glaze than you would for dipping or pouring."

So, it looks as if you could screen/sieve your ash ahead of time, but only mix into a glaze the amount you need when you are glazing. How much ash you will get will depend on how well it burned and what chunks of charred or unburned wood remained, etc. that is removed by screening/sieving. Some things can be mixed and stored in volume without spoiling or going bad. Some things . . . like unwashed ash . . . apparently can't.

And, a final caution . . . do not store your hot/warm ashes in a plastic 5 gallon bucket; use a metal bucket.



#3 TJR

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Posted 22 December 2011 - 10:56 AM

Buckeye;
The differance between washed ash and unwashed ash is that unwashed ash is runnier. It has more fluxes in it that are soluable in water.
Always use a dust mask and gloves as ash is very caustic. Unwashed ash is way more caustic as is has soluable lie in it.
A good recipe to start at is;
Ash 50%
Any stoneware clay 50%

Redart will give you a dark glaze. I tend to use 50% ball clay. I came across a bucket of Goldart which is a stoneware clay so I am going to try it in a glaze.
Another recipe I am working on is;
Ash 33%
Ball 33%
Custer Spar 33%
It seems that the more materials you have in an ash glaze, the better it works. Then try some colourants, such as-.5, 1, 1.5, 25 cobalt cabonite as a line blend.
Ash glazes run like crazy, so make sur you test on a cylinder and leave the bottom half unglazed. Set it on a broken kiln shelf or softbrick scrap. This is for Cone 10 reduction.
When I get to my studio, I'll send you more recipes to try.
TJR.

#4 TJR

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Posted 22 December 2011 - 11:01 AM

Buckeye;
Caution! I am reading over my last message. The cobalt pecentages are ;one half a percent, one percent, one and a half percent,two percent. I missed out a decimal point on the 2.5%, You never need any more than 2% cobalt. Very expensive and a very strong colourant.
TJR



#5 buckeye

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Posted 22 December 2011 - 11:04 AM

Buckeye;
The differance between washed ash and unwashed ash is that unwashed ash is runnier. It has more fluxes in it that are soluable in water.
Always use a dust mask and gloves as ash is very caustic. Unwashed ash is way more caustic as is has soluable lie in it.
A good recipe to start at is;
Ash 50%
Any stoneware clay 50%

Redart will give you a dark glaze. I tend to use 50% ball clay. I came across a bucket of Goldart which is a stoneware clay so I am going to try it in a glaze.
Another recipe I am working on is;
Ash 33%
Ball 33%
Custer Spar 33%
It seems that the more materials you have in an ash glaze, the better it works. Then try some colourants, such as-.5, 1, 1.5, 25 cobalt cabonite as a line blend.
Ash glazes run like crazy, so make sur you test on a cylinder and leave the bottom half unglazed. Set it on a broken kiln shelf or softbrick scrap. This is for Cone 10 reduction.
When I get to my studio, I'll send you more recipes to try.
TJR.


I appreciate the information. The biggest reason I wanted to try that recipe is because it fires at cone 6. I guess I could use cone 10, I know there are a lot more cone 10 recipes out there.

#6 JBaymore

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Posted 22 December 2011 - 11:56 AM

I've been using a number of wood ash glazes for at least 30+ years here.

Unwashed ash contains soluble compounds of sodium and potassium, with the higher percentage there being potassium. When the ash is washed, this content is what mainly is taken out. It is what makes the raw mixture caustic (lye). Washed ash supplies a very large percentage of calcium oxide in a glaze melt.

Sodium oxide and potassium oxide are powerful fluxes on silica across most all temperature ranges. Calcium oxide is more of a mid to higher temperature active flux on silica. So if you are thinking of firing wood ash glazes at Orton cone 6..... you might want to consider using unwashed ash.

I deliberately use glazes composed of both washed and unwashed ash. More of them are unwashed than washed. I mix them in 40 gallon batches in garbage cans, and replenish into those batches as they are slowly used up. They store for long periods just fine. The water chemistry is adjusted with a tiny bit of epsom salts or a few drops of acid (tinner's solution), if even needed, occasionally. Most of the time they do not need this attention at all. All contain 1% bentonite as an addition on top of the recipe.

When glazing with the unwashed ash glazes, I pay attention to care of my hands. And wear safety glasses to protect my eyes from possible splashes. I use industrial quality toilet bowl brushes with fiberglass handles (not wooden) to stir up the glaze batches. I do not wear gloves when I occasionally quickly dip into those glazes, but always there is a bucket of clean water right next to the glaze bucket and my hand goes immediately into that clean watter an instant after setting the piece down. I use (Japanese) glaze ladles for a huge percentage of the application work of these glazes. And after glazing lots of good hand cream (bag balm).

Soluble compounds tend to be a bit more variable from one batch of ash to the next than the results from washed ash.....which is more like using calcium carbonate (whiting). So the glazes are checked and slight variations in proportions of materials are made to compensate to retain some consistency in the fired result (example... silica content is raised/lowered a tad).

If you want to experiment with this ash glaze idea do a simple triaxial blend with wood ash on one point, any feldspar on the second point, and any clay on the third point. You'll find enough there to keep you busy for YEARS.

1/3 any wood ash, 1/3 any feldspar, and 1/3 any clay is usually a decent starting point glaze at cone 9-10. For cone six maybe simply substitute nepheline syenite for the feldspar. If you want some basic iron and/or MnO colorants in there .... use a red clay or something like blackbird for the clay content.

best,

.......................john
John Baymore
Immediate Past President; Potters Council
Professor of Ceramics; New Hampshire Insitute of Art

http://www.JohnBaymore.com




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