[Essaily]

 Hasegawa Natsuc_001.jpg (59.42K)
Number of downloads: 80I searched everywhere for info about how to make this exact glaze. Does anyone have any ideas or recipes for a speckled, erupting ISHIHAZE glaze? A video is here. Thanks.  Hasegawa Natsud_002.jpg (55.6K)
Number of downloads: 79

[Round2potter]

Best i can tell, it looks like a clear or a semi opaque white glaze over a dark body, with heavy iron grog causing the speckling.

I will sometimes add a 50/50 mix of dark (iron rich) silica sand and high iron grog to a white stoneware body yielding a nice white background with plenty or flecking. the raw clay has a sort of "cookies n' cream" candy bar look.

Or adding granular magnetite or ilmenite can give similar effects when added to your favourite clear or white glaze. Pitting and uneven/ hard to control flecking can also occur.

Firing in reduction will enhance the flecking/speckling from the clay body.

-Burt

[Mark C.]

I have a high fire glaze that will do this if fired on a heavy iron stoneware body its called billy joes butterwhite-those are iron spots from the clay body not the glaze breaking thru.
Mark

[Round2potter]

Huh. upon a little googling....... Ishihaze is in reference to small stones in the clay expanding in the firing and sticking out into the glaze layer.....

IDK anything about this!

But it sure sounds like a big old hunk of heavy iron grog, maybe even use kyanite like in Soldners Raku body.

-Burt

[macdoodle]

looks like it's in part - in the clay.

Ishihaze. A "stone explosion." Before firing, many of the impurities of the clay are removed. But some potters like rougher clay, and leave in small stones that sometimes burst out on the surface during firing - called ishihaze. Often found on Bizen and other yakishime (high-fired unglazed stonewares). http://www.e-yakimon...techniques.html

[Essaily]

Thank you all for the speedy reply and information.

A video called Japanese Pottery History said there is Potash and iron in the clay body, so maybe that's it.

I was about to ask can you add GROG to the glaze or the clay to create this effect and the answers below suggested this.

What is it like round2potter to throw with the grog clay? I just bought some fine grog today, but it doesn't look so fine to me and i'm wondering how to make it finer.

I wonder if I can make a billyjoesbutterwhite by adding some iron to the body? Or Mark, do you know where to find the recipe please? Or would iron shavings from a bbq scourer do the trick? How much exactly would I need to use?

And is it food safe with so much iron in the clay?

This post has been edited by Essaily: 11 December 2012 - 03:09 AM

[Round2potter]

Hmmmm foodsafe....probably, and i am sure somebody will jump on me for this but at worst your just getting your diet fortified with a little iron, just like they put iron in corn flakes.

Food safety depends on the glaze and the clay, and the firing schedule.

I LOVE TO THROW WITH GROGGY CLAY!!!

A lot of people i have worked with complain that the groggy clay i use tears up their hands.
As a result my hands are always baby smooth.

But it all depends on what you are doing with it, and just how big the grog is. I don't really use much anything bigger than sand size pieces; half of what I add to the white stoneware (which has fine grog) is sand.

Only once has grog drawn blood for me; and I was removing the excess clay at the skirt of a pot with my finger. The pressure onto the wheelhead caused a hunk to sink itself in the pad of my finger.

I do however use fine grog in my clay,

The added strength is amazing, and i am fairly certain it helps the clay to withstand thermal shock

Also, heavy grog will catch and drag on a trimming tool; its not a problem really, but some would say a fine grogged body is easier to trim.

-Burt

[JBaymore]

Ishihaze effects are caused by small bits of granular feldspathic rocks and quartz rocks in the clay body. It comes from the Japanese 石爆ぜ.　 石 = ishi = stone 爆ぜ = haze = burst open

For the "premier" examples of this effect, research the ceramics made in the town of Shigaraki in Shiga Prefecture. The best clay for this in Shigaraki is called Kinose. The deposits of the best clay are severely depleted... and if you can get it.... it is very expensive stuff.

One interesting technique (not from Shigaraki) is to put a layer of a high kaolin white slip in a thin coating over the clay body containing the rocks. Then the rocks sort of break through the slip layer as the clay shrinks in the firing. Over this is a layer of a milky transparenty glaze.

If you want a US commercially prepared clay that is somewhat like this kind of Shigaraki Nasty Clay thing, get "Grogzilla" from Clay Planet )Orton Cone 9-10 clay).



The images you posted look more like just the effect of hematite (iron) nodules in the clay body bleeding into the glaze layer rather than "ishihaze". But it might be the resolution of the pictures so I can't see it.

best,


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

[Essaily]

Thanks to all replies, I really appreciate your info! I'll check out making the slip over grogged clay - sounds like a great technique.

[weeble]

I'll second the Grogzilla if you want freaky things popping through your glaze from the clay! This was fired to cone 5 (Clay planet lists this as a cone 5-10 clay, so you know its not really vitrified at cone 5) with a brick red glaze over it. The glaze has a bit of dark speckle, but the white flecks in this are from the clay. I did wipe the surface on the greenware back with a damp sponge to make it rougher, I was going for a thang with this one

 2bonsaiinside.jpg (107.74K)
Number of downloads: 53

Anyway, Grogzilla is crazy groggy, some of the grog is almost 1/8th of an inch so its probably not great for wheelwork. Works fine handbuilding though!

[Essaily]

I can see the pitting in your red glaze, Weeble - really like that look, like a rock surface! I watched the video again just now, to find out why I like it so much, I don't know, I think its so humble looking with no trace of the maker except for the uneven throwing and understated glaze - that's the reason. Is it food safe btw, with all those pits and bubbles? Thanks for the name of the clay. Not sure we have it in Oz. Shall make my own.

[weeble]

Ehhh, I wouldn't use Grogzilla for food, not the way I used it anyway, because its so porous at cone 5. Even for the bonsai pots I'm a bit leery, its really a sculptural clay. This was a one-off, I was trying to use the last of a brick and demo a technique for a student. It'll absorb a lot of moisture and I expect a fairly short life span on this pot, especially if someone leaves it out to run through freeze/thaw cycles. The thing the Grogzilla does that I've not seen in other prepared clays is it throws out little white lumps in the firing. Most of those 'pits' you are seeing are actual little bumps of white material that sticks up through the surface of the glaze.

A technique I've used for pitted surfaces with hand-building is to roll cornmeal or coffee grounds or some other organic material into the surface then burnish it in. It burns out in the firing, leaving a bunch of small pits that are pretty cool.