Shino question

[BlackDogPottery]

Why is it white shino glazes leave the vivid orange\red on the breaking points? I've read a few recipes that include Spodumene as well as Nepheline Syenite. I have a white glaze that can behave like that kind of shino, white and breaking orange where thin. It is also made with NephSy but not the Spodumene. So I was curious if the NephSy was a factor? I was also curious of why some glazes leave an orange haze at the border on raw fired clay opposed to others?

Thanks!

[Mark C.]

Spodume can turn glazes orangish -this is more true on stoneware 

Stoneware Iron based clays also do this at the borders

Breaking point are where the glaze gets thin-and the iron in stonewares breaks thru or adds to the color of thin glaze.

 

You did not mention what clays you are working with (white bodies or stonewares?)

My guess is its stoneware clay you are asking about.

[glazenerd]

Mark:

 agreed, but have also noticed higher % of titanium in the clay amplifies the problem.

[oldlady]

glazenerd, i think the breaking orange is beautiful and i would bet a lot of potters do too.  not a problem, a beautiful result.

[LeeU]

Maybe a topic for a future question of the week....is "it" (like the spodumene effect) a problem (as in the science/craft sense it may well be) or is it a blessing (in the sense of the  aesthetic/philosophy of the ceramicist)?  I love cracks and "flaws" in my pieces (go out of my way to introduce them)  but it does set me up for "having" to explain to the guy/gal  whispering to the person with them that "This gal isn't very good-look at all the cracks and pinholes." that actually, I know what I am doing, I just choose a different path.  Kinda like life! aaarrrggghhh

[glazenerd]

Oldlady: okay, " problem "was the wrong choice of words. I blame it on my child hood, back when avocado green, burnt orange, and turquoise green were popular.

[BlackDogPottery]

16 hours ago, Mark C. said:

Spodume can turn glazes orangish -this is more true on stoneware 

Stoneware Iron based clays also do this at the borders

Breaking point are where the glaze gets thin-and the iron in stonewares breaks thru or adds to the color of thin glaze.

 

You did not mention what clays you are working with (white bodies or stonewares?)

My guess is its stoneware clay you are asking about.

Yes its stoneware . Just to clear up any confusion I didn't mean to  make it sound like a glaze defect, I love it when it happens. 

For some reason I thought maybe the nephsy as a base feldspar had something to do with unlike other feldspars I've tried that just can't produce the same effect. 

[GEP]

It’s not related to NephSy or Shinos specifically. It’s any glaze that runs just enough (to run off of high edges), and is opacified just enough (to lose opacity where the glaze is thinner on the high edges), combined with a dark claybody underneath. I have a glaze that does this, and it is accomplished with Gerstley Borate (flux) and Tin Oxide (opacifier).

As for  “orange haze” I’m not exactly sure what you mean. In terms of Shino, spodumene used to provide a tiny bit of iron and other impurities that added some orange/peach/blush tones to the glaze. However, that spodumene has been gone for over a decade. The spodumene we can buy now looks like white sugar and does not supply any iron. Use this in old Shino recipes and you’ll get a white glaze. These days, you need to add other forms of iron in order to get orange/peach Shinos. I have a friend who fires a lot of Shino, and her favorite recipe contains GoldArt clay for that. This has nothing to do with breaking on the edges, like I said that’s another matter. Lots of Shinos just happen to be slightly runny and opacified just right. 

[BlackDogPottery]

6 minutes ago, GEP said:

It’s not related to NephSy or Shinos specifically. It’s any glaze that runs just enough (to run off of high edges), and is opacified just enough (to lose opacity where the glaze is thinner on the high edges), combined with a dark claybody underneath. I have a glaze that does this, and it is accomplished with Gerstley Borate (flux) and Tin Oxide (opacifier).

As for  “orange haze” I’m not exactly sure what you mean. In terms of Shino, spodumene used to provide a tiny bit of iron and other impurities that added some orange/peach/blush tones to the glaze. However, that spodumene has been gone for over a decade. The spodumene we can buy now looks like white sugar and does not supply any iron. Use this in old Shino recipes and you’ll get a white glaze. These days, you need to add other forms of iron in order to get orange/peach Shinos. I have a friend who fires a lot of Shino, and her favorite recipe contains GoldArt clay for that. This has nothing to do with breaking on the edges, like I said that’s another matter. Lots of Shinos just happen to be slightly runny and opacified just right. 

Oh okay I see. As for the hazing its usually where there's fired unglazed clay next to a glaze (like a footring) there's an orange haze. I thought it was iron fuming from the clay body, sometimes it's there and sometimes not depending on the glaze.  If you're familiar with clay bodies there's a popular kind from Laguna called Speckled Buff that I've noticed it on several times from pots made from other people. 

[GEP]

How wide is the orange haze? Do you mean something as wide as a Sharpie marker line? Or something wider than that?

[Magnolia Mud Research]

Back to the original question "Why is it white shino glazes leave the vivid orange\red on the breaking points?"
 
Shino is a reduction high fire glaze based on a mixture of local feldspar and clay originated in the Mino and Seto areas of Japan during the late 16th century.  The 'recipe' was lost in the early 17th century and later 'rediscovered' in mid-20th century.  An American version (using soda ash) evolved from work done by a grad student at University of Minnesota circa 1975.  A characteristic of the glaze's appearance is that the glaze is white where thick and red/orange where thin if there are no colorants deliberately added to the glaze. 
 
My current working hypothesis regarding the 'color' of the glaze:
The thickness of the glassy film is more important to the range of the wavelength(s) of the light reflected back to the viewer than the specific elements included in the glaze recipe.  Beyond a certain thickness (determined by experiment for each variant of the glaze recipe and the clay body on which the glaze is applied) all light is reflected back to the viewer, a.k.a. white is the observed color. The 'standard' colorants - iron, copper, cobalt, rutile (a.k.a. titanium), nickel, manganese, … – will 'do their thing' when added to a straight cone 10 shino recipe.
 
My experience is with ‘American’ versions of the glaze and a thin 'halo' region edge usually appears where the glazed area stops and an ‘unglazed’ area begins; the ‘halo’ probably comes from the dissolved ions in the glaze water. 
 
A true shino is a very 'stiff' (high viscosity) melt.  Any 'breaking' over edges (carved or relief textures) is due to the effects of the local surface tension of the melt (high for shino) and not to the bulk movement of the melt.

 

In my work, the application thickness always determines the color of any shino I have used.  Thick applications will be white, thin will usually be a red/orange.  On dark clay very thin layers will golden, medium will be red-orange, and thick will be white.  On porcelain, very thin layers are orange, and medium will be yellow and thick will be white. 

 

For me Shino allows significant opportunities to decorate and just use one glaze by varying the glaze thickness.
 
LT

[Pres]

One of my favorite cone 10 glazes at Mansfield State College/University  was the glaze called Spodumene. I never have had the formula/recipe, but it was a great orange red opaque glaze that broke well over textures, even fine throwing marks. Speckling made the surface textured, and it worked well with a variety of other glazes.  I am not trying to hijack the thread, just reminiscing about a non Shino Spodumene glaze.

 

 

best,

Pres

[Magnolia Mud Research]

Pres,

you just ignited  an idea for this semester 

thanks!

LT

[Joseph Fireborn]

I am still not sure what exactly qualifies as a shino myself. I have spent a fair amount of time modifying a single glaze to get shinoish results. I think of a shino as a glaze that when thin is a reddish orange, and when thick is a beautiful solid white, not cream, but white, I also think it shouldn't be glossy, but slightly satin.  

I also think that a good shino is one that has pinholes and crawls. I don't think this is caused by the glaze as much as it is by the application over a rough body of work. When I look at old shino ware the clay itself has tons of grit and sand in it, I think the thickness of the glaze when poured or brushed over the clay doesn't allow it to fill in these little holes and marks which later cause the glaze to crawl more later on. I am currently working on a "fake shino" if that is what you can even call it. I don't really know if a "real shino" can be achieved in electric, depends on who you ask I guess. 

Here is an example of the glaze that I have been working on for a while(although my final application will be much different):

This is my most recent result of it. I am still not happy with it, although it is showing promise. It is still way too glossy and it doesn't have the pinholes and crawling that I want, also slightly brownish/red instead of orange/red/peach. I will be able to fix that part with my application soon I think.  The color is also slightly off, I plan on fixing that by adding a bit of redart in place of some of the EPK in the glaze.

Here is the same glaze on a bowl on a crackled slip:

You can see that when it is thick, there is 0 red/brown showing.

Like LT said above, I really think the best part of a shino glaze comes from the ability to brush on a thin coat then pour over a thick stiffer coat so that you can get the variety of colors. That is what I did on the tile above. I brushed a thin coat then dripped on a thick coat and let it run towards the top of the tile.

Looking at:  http://www.e-yakimono.net/guide/html/mino.html

This is basically the most accurate idea I have in my head of a shino pot. I believe the glaze melt itself needs to be super stiff, if it is a fluid glaze I don't think you are going to get these pinholes in the surface, which I think comes from the texture in the clay when the glaze was poured over the pot in a naturally random way, or bubbles popping in the wet glaze from the bucket.

If the glaze was fluid then the holes would fill during the firing.

When I was working with another glaze one of the best parts about it was that when I first mixed up the glaze it would have a lot of bubbles, when I poured it on a pot, it would come out with tons of little pinholes just like the pot above where the bubbles in the glaze were trapped then popped on the pot. When I fired it, I got results very similar to the surface in the pot above. The glaze was super stiff. 

In my research to get more natural looking results with more variety, I have learned that the less you fuss with the glazes the more natural they become, and I think a lot of people are overworking their glazes for consistency. If you think about ancient times, they didn't have power mixers. They mixed it by hand the best they could with whatever tools they had at their disposal. They weren't sitting there with a talisman rotary sieve and a fancy drill mixer mixing their glazes to go through 120 mesh sieve perfectly. Also, we have to remember that the pots we see on the internet and in pictures are usually the best pots people pull out, there are thousands of crappy shino pots that look like every other crappy shino pot. We idolize the best ones thinking that is a consistently achievable result, but in reality, beautiful randomness is just that, random. There is a reason when potters who work with shino's get a good result they post it and say, "Ahh I love when a shino works!"

just my thoughts about it all, has anyone defined what a shino means nowadays? Cause I see commercial glazes called shino that are green and blue...

[Magnolia Mud Research]

 

 

I played a couple of years firing at cone 5-6 reduction and was unable to find a “true” shino type glaze — the temperature was too low!  

I did find a glaze that “appeared” like shino.  The recipe was published in Clay Times (I think).  It was actually a mixture of two cone 5-6 glazes, one was based on Alberta slip, the other was some GB based glaze.  The pots looked OK, lots of compliments at showings.  One good characteristic was it “played well with others” — real Shinos choose their playmates carefully.  

 

LT

 

[Joseph Fireborn]

Yea... I haven't put much effort into it at cone 6 anymore, because I just don't think it is really possible to get a good looking one. Maybe one day. But still, what is a real shino!? 

[Pres]

Joseph, and all, 

I have been working with Cone 6 since the mid 80's. At that time there were some great commercial glazes, ART and Minnesota clay being two of the best at the time when considering price vs quality. AMACO also had a good product but sold in 1 lb bags! Pricey.  It took a lot of research to find good glaze recipes, and a lot of experimentation to come up with my own. That added on to ending up with a safe inventory for the HS studio, that was as safe as I could make it knowing how accidents do happen, especially around teens. Point being, i am sure that an acceptable Shino with all of the wonderous defects is out there for Cone 6. It may take a bit more time with the understanding, or even take going to a Cone 6 reduction, or local reduction, but i think it is possible. So don't give up on it.

On another note today, I was looking at a brick wall that had bricks that looked like they had an  aggregate of recycled tiles in 1/8" pieces. I was thinking it would be nice to throw for that sort of texture, but then I realized my hands would look like I had put them down the garbage disposal! Nope.Maybe for handbuilding though.

 

best,

Pres