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MMead

Suggestions And Advice For Beginning Raw Glaze And Once Firing Specifically Cone 6

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Hi John - I do hope you had a brilliant trip without too much jet lag.

 

I'm keen to learn once firing in an electric kiln and luckily I'm very interested in creating my own glazes.  I'm located in South Africa so raw materials are a challenge (Strontium Carbonate for example is not to be found and other common N. American materials are incredibly expensive).  I have researched Steven Hill and Dennis Parks as much as possible via internet.  I have a few questions to start with:

 

1. My first test includes the Turner's White recipe - however we don't have access to EPK Kaolin and the local supplier suggested China Kaolin.  My gut is this was might not have been a good suggestion as it all settled out of the mix.  The Turner's white and my red have already flaked off or shivered off the pots even before firing.  I think this means I need to increase the bentonite to 5%. Your thoughts?

 

2, due to being new to pottery I have recycled stoneware clays which seem to grow black stuff underneath.  The local supplier suggested this was great and many potters like this.  My research seems to indicate this could lead to problems of increasing the amount of burn off required - your thoughts?  (also because I'm new I'm throwing small test bowls instead of tiles for the practice.)

 

3. I have a red glaze I'm trying and I understand that reds like to fire fast - while I'm using S. Hills firing schedule (for electric kilns) I'm thinking putting the reds at the bottom of my kiln where it seems to warm the fastest may assist this issue of slow firing (but I'm expecting my clay to fire out a lot so either pin holes or gray glaze could result).  Is the top better as hot air rises and that's where the chimney is.

 

4. Are there any good books with information and recipes or perhaps internet mentors?  I have found Digital fire to be of immense help in understanding the glaze ingredients.

 

 

These first tests I decided to use straight forward recipes like Turner's white because of the large firing range and also due to a belief that it sometimes will work.  I have bisqued pots in with the raw as "control" subjects all sprayed in the same way.  There is a local pottery who fires earthenware in a propane fiber kiln.  He somehow uses alcosperse to hyper-flocculate his glazes and then he uses epsom salts to deflocculate?  I'm not sure I understood and I'm not sure he wanted me too - but somehow this makes the water requirement less and also assists the glaze sticking to the dry greenware.  Your thoughts?

 

Thank you for any help, advice etc. 

 

 

 

 

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Are you writing to John, or are you writing to the rest of us?

You sure ask a lot of questions!

I will tackle two.

1. Raw glazing ,which I have discussed previously, is done one of twoway.

method A- glaze insides of pots when leather hard. When bone dry, glaze the outsides. Much expansion and hair line cracking on handles.

2. Glaze leatherhard in and out. Glazes must be adjusted to be almost slips. Should have 25-30% plastic clay in your recipes. Take out your kaolin and add ball clay. add 5% Bentonite.

I have never raw glazed at cone 6. i fire to cone 10. should work though.

Be prepared to have more losses. Handles falling off etc.But way more fun than glazing a pink pot.

TJR.

Oh! Oh!. Forgot the second question. If black mold bothers you, you can add a cap full of bleach. Stinks though.

T.

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Hi TJR- I addressed it to John because he's the moderator- but I'm keen for experienced advice please. I do have many question as I've read a lot and some is contradictory. Also I am not finding a whole lot of info as one does with bisque glazing and firing.

 

T- if I add ball clay won't this increase the iron amounts the glaze can react with? I appreciate the explanation of the consistency needed for the glaze. Mine is obviously still to thin.

 

I can't stand those pink pots- puts me right off! As for losses- I reckon since I'm a beginner it will only make me better faster.

 

Do you spray, dip or pour? After reading Steven Hills many articles I decided on spray to decrease over wetting as much as possible.

 

Thank you so much for your input!

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Hi TJR- I addressed it to John because he's the moderator- but I'm keen for experienced advice please. I do have many question as I've read a lot and some is contradictory. Also I am not finding a whole lot of info as one does with bisque glazing and firing.

 

T- if I add ball clay won't this increase the iron amounts the glaze can react with? I appreciate the explanation of the consistency needed for the glaze. Mine is obviously still to thin.

 

I can't stand those pink pots- puts me right off! As for losses- I reckon since I'm a beginner it will only make me better faster.

 

Do you spray, dip or pour? After reading Steven Hills many articles I decided on spray to decrease over wetting as much as possible.

 

Thank you so much for your input!

I actually am not raw glazing at the moment as I gas fire my work at another potter's studio, and packing it up green for transport would not be practical.

I dip my glazes at leather hard. large bowls are a bit tricky. Steven Hill sprays bone dry. I do not have a spray booth set up, but I like the immediacy of pouring and dipping.

If you post your glaze recipe, i will take a look at it. I say the increase in iron content for the ball would be negligible. you are also firing oxidation in an electric kiln, so you should be O.K.You are not adding ball clay, you are removing kaolin and replacing it with plastic clay.

T.

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the Turner's White Recipe from CAD

 

10%  Dolomite 

9%    Whiting     

25%  Soda Feldspar 

20%  Custer Feldspar  (this isn't available here, I understood it to be a potash feldspar so that's what I replaced it with - Potash Feldspar)

18%  EPK Kaolin (again not available - the best suggestion was to use China Kaolin - but as I said - this settled right out)

 6%   Talc

12%  Silica

 

Add: Bentonite 2%

 

As per your suggestions I should replace the Kaolin with ball clay (can I just "grind" some of my dried clay body for this - so it matches best?)  this won't be the 20-30% you suggested - but's it's close.  Then I should increase the bentonite to 5%.

 

The other recipe is an Emmanuel Cooper recipe that I'm certain is going to have trouble as the silica content seems far to high.

 

40% Feldspar (I used potash again as I've read about the problems with high soda feldspar percentages)

 4% Zinc Ox

 3% Dolomite

15% Whiting

 5% China Clay

33% Silica

Add .5% Chrom ox

       4% Iron ox - (I assumed red)

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Mead;

The first glaze is doable. Direct sub the ball to replace the kaolin.

Custer is a pot spar so any other pot spar should work

Up your Bentonite to 5%.

You should be laughing.I don't know about grinding your ball clay. Easier to just buy or borrow a bit.

2. Second glaze is tougher. you have a lot of silica and very little clay. This looks like a shiny glaze. You can try subbing the ball and adding 5% bentonite in.

Make sure you test on leather hard tiles.

If the glaze doesn't shrink enough, it will just hang away from the tile. The idea is to have the glaze shrink at the same rate as the pot.

You may end up with a couple of glazes for raw dipping and some for spraying.

Lots of salt glaze potters raw glaze as they use slips on the outside and glaze the insides.

TJR.

p.s There is a limit to how much bentonite you can add in. At about 20%, your glaze will turn to jelly.

T.

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The firing is finished.  There were numerous technical issues.  To express a few:power at my friends kiln kept tripping just before I reached peak temp - my attempt at a soak nearly liquified cone 5 and 6.  I made the decision to leave the bungs in when the fire finished at 9pm - I'm sure this was not my best decision especially as the kiln overfired.  What I am left with is:  burned out reds and a few other odds.  The controller is totally manual and 30yrs old at least.  I really struggled to control kiln temps.  My cones were either up or liquid.  There was never a bending time. (I check the kiln every 30min/60min)

 

Several questions beg an answer if you could please be so kind as to suggest what happened:

 

1. there is a lot of pin holing - more on the bisque commercial glazes used as control subjects.  Why?  Especially since there was a LONG ramp up between 500'C and 1000'C (this also was a problem in that it took longer than it should have).  I very meticulously dusted the post before spray glazing.

 

2. there is much cratering in pinhole type effect - I'm wondering: is the alumina calcine I put down so carefully able to fly about in the kiln and cause this (specifically on lower shelves).

 

The other questions aren't so imperative as I will need to reformulate to the raw glazes with higher clay content.  Much of the commercial glaze chipped off/ fell off before firing - what stayed on fired on well with little pin holing in the raw clay.  I will also need to refire at the right temps to understand the colors and thicknesses etc.

 

As soon as I work out how to up load my pics I will put them in the gallery for learning purposes.  so long I have them on FB..https://www.facebook.com/melissameadinprogress

 

Thank you for the help I received here thus far.  I'm looking forward to the next glazes and firing.  I'm also on a hunt for a kiln of my own.

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You got some nice soft luster on some of the pieces, and I liked the iron spots on some of the bowl outsides. There is some obvious problems with liquifying glaze on the bottoms of some of the bowls. This will take a bit of a learning curve, but the first firing was not a disaster. Keep on keeping on!

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Thanks Pres-

I was definitely not shooting for a luster- 😉. On the positive side I feel any firing that doesn't blow a pot out or weld one to a shelf is success. Can't wait for the next one!

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I raw glaze at cone 6 and I think that the clay body is most important to its success. Some can't take the glazing, some bloat in the firing. It takes a while to get a handle on it and you are well on your way.

I raw glaze greenware bone dry and most of my glazes do not have a lot of clay in them. I glaze the insides one day and glaze the outsides the next. My pots can be seen at www.coryellclayworks.com

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