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Biglou13

Food Safe Cone 6 (5) Ox Glazes Please

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I sort of have a customer. Sort of a first commission.....

It's more so trade pottery for food, it's bakery (European style organic sourdough starter thick crust kinda bread)

Thing is only one of my glazes in my "pallete" is food safe and not crazed.

I'm sort of picky(limited) in what I like creatively and what works for me.

My pallete now includes a black (hairs fur ish) (food safe), Bob which is a oribe (ish) green, And the many effects from one shino (ish) glazes.

 

And when they mentioned trade for bread for life or something like that. First I was flattered then I thought to myself, you know how much good bread, I can eat. (I'm a big guy). Well sounds like a goo deal all around the even offered me a shelf to sell my ware at bakery.........

 

Fast forward I need a few more food safe glazes........

 

I make test glazes tomorrow

 

Maybe this will give you some direction what interests me.

 

Tomorrow ill be making

Celadon (ish)

Randy red

A few albany based , Rutile and brown jug

Tenmoku(ish)

 

These have been tested in other studios as food safe and I like the colors.

 

I'll also finish tweaking shino (ish) glaze so not to craze.

 

Any suggestions and recipes would be greatly appreciated .

 

Pictures or links would be greatly appreciated.

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Have you seen this article in the Ceramic Arts Daily?

 

Recoloring a Classic: Trying New Colorants in a Classic Pottery Glaze Recipe Can Lead to Some Great Results

 

http://ceramicartsdaily.org/ceramic-glaze-recipes/mid-range-glaze-recipes/recoloring-a-classic-trying-new-colorants-in-a-classic-pottery-glaze-recipe-can-lead-to-some-great-results/

Marcia Selsor likes this

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A solid clear glaze and some engobes/underglazes could be a useful thing to have in your repertoire.  It would open your colour palette back up, maybe.

 

I haven't personally tested a clear glaze recipe I can recommend for ^6 oxidation, but there are many to be found here, I think.

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Lou,

 

Watch oribe-type copper glazes for (Western Style) interior container surface food use........ copper is notoriously difficult to "hold" in a glaze.  When the percentages get up there to get beautiful Oribe-stlye greens....... they can start to leach copper.  If there is any black flecking in the color... that almost for sure will leach.

 

The tiny percentages in copper reds are not an issue.

 

Copper is not greatly toxic, but it changes the taste of food if it leaches. 

 

However, for the tiny fraction of the population with Wilson's Disease, it can seriously affect them.

 

best,

 

.................john

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If you are talking about the glaze with 2% copper from the link above......... I just ran it in Insight.  Whikle it is within limits in most cases (looked at multiple limit formulas) the silica number is at the bottom end of the range.  So that says that the glaze might not be as durable as one could want in that cone endpoint range.  Worth some testing, for sure.

 

best,

 

................john

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I mixed up a batch of this clear Cone 6 from a Michael Sherril workshop to use over textured and RIO pieces and had good success when sprayed on...but these were decorative pieces, not functional wares.. It would be nice to get a confirmation that this is indeed food safe:

Ferro Frit 3124 -- 32.2%
Feldspar (Soda F4) -- 25.8%
Silica -- 19.4%
Whiting -- 12.9%
Kaolin EPK -- 9.6%
Total -- 99.9%

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In order for a glaze to have issues with leaching relative to the questions of food safety, there has to be something in the glaze that is potentialy toxic.  Just looking at that recipe as it sits, if you know your raw materials oxide sourcings, there is nothing there that is particularly harmful.  So that is a good starting point. 

 

However.... add a potentially toxic colorant... and that potentially changes things.

 

This says nothing about visual durability as to dishwashers, knife marking, and so on.

 

best,

 

.................john

ChenowethArts likes this

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Just ran it in Insight.  It is a bit oversupplied with CaO (which weill tend to cause it to react with underlying clay bodies and will cause it to tend get micro-crystaline percipitation on the surface in slow cooling situations), but other than that..... is solidly within multiple different limit tables.  Should be a reasonably stable cone 6 glaze as it sits.   

 

But the ONLY sure waty to know is lab testing.  If you add colorants........ that is the definitive answer.

 

PS:  The "lemon test" getting recommended all over the place is a 'rule out' test not a 'rule in' test.  Meaning if it fails the lemon test, it is not worth doing lab testing... it is unstable.  BUT if it passes the lemon test it is NOT necessarily going to "pass" an actual acetic acid lab test. 

 

best,

 

....................john

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The glazes resulting from "Recoloring a Classic..." from Ceramic Arts Daily brush on beautifully, so one can splurge and make up several small batches and have enough to brush glaze quite a few pots.  I made up 500g batches and am considering more.

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Re : falls,creek shino (ish)

 

Ok I'm sold !!

 

I adding this/these to tests this Wednesday

 

Are you portion calcifying albany/alberta slip to cone 022. Per alberta slip.com?

Or just raw alberta/slip?

Anyone test with arroyo slip?

Anyone test with lithium substitutes?

Anyone test with spodumene?

If not any drying cracking issues?

 

Anyone run tests on porcelain/porcelain(ish) bodies.....crazing issues?

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Re Fall's Creek Shino(ish)

 

I have had no problems with drying and cracking, and I do not prefire any of the Alberta slip.  The only other slip I have tried is Albany and had no problems there, but it is so precious that I switched to Alberta.  I have tried several clays but the closest I have come to porcelain is Laguna''s cone 5 B mix - worked fine.  Overall I think that of the colors (Mason stains and oxides) I have tried I prefer the glazes when they are on clays containing some iron - but that's probably just personal preference.  It seems to me that brown clays accentuate the shino(ish) quality.

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re: Fall Creek shino(ish)  I have mixed up a number of batches of the FCSish with copper carb, cobalt carb, and mason stains.   I use 2% on copper and cobalt and 5% on Mason Stains.  I have even tried a 1% on the copper which was nice also.  Just a little lighter green.  I have used all of the versions of FCS ish on brown speckly clay and on bmix and porcelain.   I like this glaze on all of the clays. However, I spray it and I like it best on white clay.    The first pic is of two green shino-ish bowls  The 2nd pic is the underside of a green shino-ish bowl.   The 3rd one is with vivid blue Mason stain and the 4th one is FCS ish with yellow ochre.   Hope all attaches.

post-14790-0-34094200-1393907183_thumb.jpg

post-14790-0-10805800-1393907226_thumb.jpg

post-14790-0-33310700-1393907279_thumb.jpg

post-14790-0-29089500-1393907383_thumb.jpg

post-14790-0-34094200-1393907183_thumb.jpg

post-14790-0-10805800-1393907226_thumb.jpg

post-14790-0-33310700-1393907279_thumb.jpg

post-14790-0-29089500-1393907383_thumb.jpg

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It seems to be a no fuss, no muss, sort of glaze.  That's all I have used with the fcs, is a standard firing schedule.   I forgot to include just the base recipe in the pictures, but it's a nice brownish.   It doesn't run or move, lighter application gives more of the brown tones in any of the colors.   I had one weird thing happen when I first started using it.   With the copper carb fcs.   The outer layer sort of rubbed off when the customer put cranberries in it.   After having run a lot of tests here at my home, I came to the conclusion it was a anomaly.  I have not had a problem with it since.   I have even layered up the colors.   blue over green is nice.  

 

Roberta

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 I had one weird thing happen when I first started using it.   With the copper carb fcs.   The outer layer sort of rubbed off when the customer put cranberries in it.  

 

Cranbetrries..... seriously acidic.  Surface color or quality change.......... glaze instability???????

 

That would be a "red flag" for me.  I'd want to know for sure WHY I got that result. If it happens once... it can happen again.  And I'd want to know if it is happening more... I just don't KNOW about it.

 

Lithium carbonate is a problematic raw material.  It is slightly soluble.... and that can cause REAL problems.....becasue it can impact the clay/glaze interface layer in bad ways.  Plus it is molecularly light... so a deceptively small weight of material is adding a LOT of lithium oxide molecules in the melt.  Li2O has the lowest COE of all of the oxieds we use.  This can cause issues with both fit and glaze stability.

 

Home tests don't really suffice for answering the question....... "Does it unacceptably leach copper or other colorants?" or the slightly less important question, "Will it stand up to long term repeated food and serving use"? 

 

Here's a quite from Ron Roy about that glaze: 

 

"This is a tough problem, not because of the GB but because that much

lithium Carb can be big trouble - anything over 2% can cause dramatic fit

problems - like shivering and crazing on the same piece - I don't recommend

this kind of glaze on anything that could be used for food - think about it

- flakeing pieces of razor sharp glaze in food - in people!"

 

If you don't know who Ron is....... look him up.

 

best,

 

........................john

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