attached is a Masters thesis on cone 6 oil spot glazes which is very thorough and produces wonderful results. I corresponded with the author for a while and he repeatedly emphasized to put the glazes on very very thick. One problem I had with this was taking his advice to seriously. I put them on so thick that on vertical surfaces that they slid all the way down to my kiln shelf and then some.

Since thick is a relative term I never really know what people mean by thick, thin etc in terms of actual measurements. I wish there were some clear standards of what these terms meant..

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Lawrence, 

can you show pictures of the pots you tried cone 6 oil spot glaze on, even if it ran off the pot? Unless of course you

broke them all with a hammer.

Juli

You can see examples in the Masters Thesis that "Oil Spot" glazes can be problematic when gravity is not your friend.

I've found the iron bearing glaze under the oil spot cover has to be fairly stiff at melt temperature or you face these sliding problems. 

Try three layers of the "Orange Street" recipe below as the high iron glaze under the white oil spot top coats.  Orange Street stays where you put it and doesn't allow the cover glaze to slide.

attached are a couple of pictures of oil spot pots. Unfortunately the colors are substantially dampened by the  poor quality Laguna iron oxide unintentionally. Norm Stewart has discussed this problem on this forum. At some point,  I've gotta get back to re mixing these glazes and trying it again, t inhis time a little thinner and on more horizontal shapes as illustrated in Vikery's work.,

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I have had really good luck with the recipes that I got from Alisa Clausen's page.  The bottom glaze is really stiff & honey like, so it bubbles up through the overcoat making the oil spots.  I have been able to vary the bottom color and also the top coat color as well.  The problem is that if the 2 glazes form a eutetic, then the glaze will be all over your shelves. I don't know how to tell you how thick to put it on, you just have to experiment.  With crystalline glaze, thay actually have tools to measure glaze thickness, as thickness is paramount for that glaze.  jhp

Alicia Claussen seems to have several pages. Which one are you referring to? On that page, which glaze are you referring to.

 I've developed my own glazes depth measuring tool  that works pretty well. If you can give me your estimate of the approximate thickness of each layer, I can try to translate that to my spraying.

Just go to her oil spot page and it is #1 and #2.  You just use one over the other.  She gives the recipes and explains how to use them, as well as how to change the color of the cover glaze.  jhp

Found it ... Thanks

'Thick' can change from glaze to glaze.  I have a transparent glaze that is fine as a very watery single brush coat.  A second bush coat results in a beautiful but completely unpredictable set of pale blue and white feathers that tend to settle in patterns incised in the clay body or at the bottom of the glaze. 

Then I have a floating red that is fine with a nearly whipped cream texture that requires three brush coats, or a generous dip,  and don't spare the horses.

It seems that experimentation is a necessity.

I never could tell if folks meant "thick in the bucket" or "thick on the pot".  

I just fired a load with small pots with the two glazes John Britt listed in a CeramicArtsDaily piece;

What I got by brushing 3-4 coats of each glaze was what looked like a white glaze on a clay body with manganese granules in it. I fired to cone 6 with a 30 minute hold.  I'm not sure how to proceed.  Longer hold? Thicker layers? Different glazes?

I obtained nearly identical "non-results" with the Cone 6 combination glazes recommended by Jon Britt.  I've found almost any other high iron glaze, like Orange Street, used as a base coat works better.

Bear in mind that red iron oxide does not reduce to black iron oxide at Cone 6 temperatures and below, so the Cone 9/10 "oil spot mechanism" of red iron oxide releasing oxygen bubbles from the base glaze suggested by Jon Britt will NOT work at Cone 6.

The mixing mechanism between the two types of glaze at Cone 6 has to be carbon dioxide gas being released from carbonates or thermal currents.

Alisa Clausen tried these Britt recipes and other recipes (substituting a Scandinavian boron frit 169 similar to Ferro 3134 for gerstley borate or any frit listed, and a local balanced feldspar similar to Custer Feldspar for all references to feldspar). Note the the hyper-links #1 and #2 adjoining some of her photos no longer work, but the linked recipes still exist on the page with her other oil spot photos.

These are her results and non-results with this firing schedule below. 

https://www.flickr.com/photos/glazes/sets/72157605126678933/

Alisa Clausen Firing ramp with an electric controller is:
100c p/h to 600c (212f - 1112f)
150c p/h to 1140c (302f - 2084f)
80c p/h to 1220c (176f - 2228f)
15 min. soak
cool down max. to 900c (1652f)
Hold 30 minutes

As proof that red iron oxide reduction is not the mechanism at Cone 6, I replaced the red iron oxide in Jon Britt's iron glaze with black iron oxide. As black iron oxide is a flux at Cone 010 and above, the base glaze is more fluid than the refractory red iron oxide version, so the top coat does a good deal of sliding about on the black iron lower glaze.

The top layer in this instance is one Alisa Clausen used with Praseodymium Yellow Stain.



Rodney Allen Roe said:

I just fired a load with small pots with the two glazes John Britt listed in a CeramicArtsDaily piece;

What I got by brushing 3-4 coats of each glaze was what looked like a white glaze on a clay body with manganese granules in it. I fired to cone 6 with a 30 minute hold.  I'm not sure how to proceed.  Longer hold? Thicker layers? Different glazes?

What happens if you put some RIO and some BIO in the glaze, Norm.  Would that give you the reducing and fluid portion of the glaze from the BIO and the crystalizing portion from the RIO? 

I'm not knowledgeable about glaze formulation, I'm just working on what I've read about what to use different chemicals for in cone 6 glazes.

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