[armen]

Hi Folks,
Hoping I can find someone to give me some advice. The studio I'm in has the oft-published Malcolm Davis Shino. As those who have used it know, it's a finnicky glaze. I was wondering about the effects of the following variations in application on a) the amount of crawling, and b ) the amount of carbon trapping. Crawling in particular is something I'd like to avoid as I'm putting this on functional ware. In the best case, i want to decrease crawling and increase carbon trapping.

What are the effects of
1) Drying time before firing. 1-2 weeks vs immediately before loading kiln.
2) Moisture of drying area. Our studio has a 'damp room' which allows for a much more moist atmosphere for drying, vs. drying in the studio.
3) Dampness of the bisqued ware before application. I have seen people mention moistening the bisque before applying MD shino.
... What is the difference between
... a. applying to dry bisque
... b. applying to sponged bisque
... c. applying to soaked, then partially dried (overnight) bisque
4) Thick application vs. thin application


I'm going to do some tests, but would like to hear anything and everything that people have to say about MD shino or carbon trapping shinos in general. our md shino has a strong tendency to crawl.

*EDIT** I should add that these are getting fired in ^10 reduction in a gas kiln

[Mark C.]

When I use MD shino its in the salt kiln and it is known for crawling-thats part of what it does.I usually use it on the exterior only. I suggest glazing at least 1 day ahead of time and when its dry use your hand to rub the surface out (smoothing) the surface down some. Expect a crawl and maybe you will luck out. There are other shinos that crawl less. If its to thin it will not crawl as much but it looks thin as well. I have sprayed water on pot 1st to keep the application thin. I never put it on thick.
Mark

[armen]

Mark C., on 24 September 2012 - 08:27 PM, said:

When I use MD shino its in the salt kiln and it is known for crawling-thats part of what it does.I usually use it on the exterior only. I suggest glazing at least 1 day ahead of time and when its dry use your hand to rub the surface out (smoothing) the surface down some. Expect a crawl and maybe you will luck out. There are other shinos that crawl less. If its to thin it will not crawl as much but it looks thin as well. I have sprayed water on pot 1st to keep the application thin. I never put it on thick.
Mark

Mark, when you say smooth the surface, do you mean to get rid of crystal formations or what? I don't know what it (soda ash?) but something crystalizes on top of md shino.

[bciskepottery]

For good carbon trapping, glaze well ahead of the firing. You want to give the soda ash a lot of time to move through the pot to the outside walls and form crystals. One week, two weeks. The longer it sits on the shelf, the more crystals (fuzzy white stuff) you'll get. A friend of mine actually skims off some of the soda ash "tar" that separates at the top of the glaze bucket, pours it over her bisque, lets it soak in and then dips in the mixed glaze. She throws porcelain exclusively. To avoid the little bubbles in the surface, after mixing the glaze use a sieve to remove them and then dip your wares. I've heard that storing the glazed item in a closed box promotes soda ash crystal growth.

[Mark C.]

I agree on letting the soda dry and form a haze-I use this differently in a salt environment . When I glazed pots long ago for reduction firing with this glaze I let them sit some days and did not rub them down-But I did not mind the crawl.Let the crystals form and do not disturb them.
The bubbles we have also sieved out with a dip sieve-These are what need to be rubbed out when formed on pot that I spoke about-best to avoid them if you can.
Salt works on this glaze with a very mild fluxing compared to reduction firing which is drier feeling on surface.The soda in glaze turns a nice color in salt as well. We often add soda to enhance the orange color on bottoms of pots.
I have some great Warren Mackenzie pots with good shinos on them-one is smooth one crawled-the one my cat broke crawled as well.That was a sad day.
Mark

[JBaymore]

Carbon trapping with high soluble soda content glazes like the usual Maclom Davis shino recipe is affected greatly as a function of the firing cycle. For very heavy carbon trapping you need to start heavy reduction at a very low cone... like about cone 012. The serious carbon trap schedule is kinda' incompatible with a number of other glazes which react badly to such heavy reduction at such a low cone.

And if you did not "do the job" at bisque in order to burn out the carbonaceous materials in the clay body (had lots of oxygen in the kiln atmosphere) AND you start heavy reduction this low... expect some body related firing defects to crop up.

You can mix up a super saturated solution of soda ash and hot water until the water will not disolve any more of it..... and then spray it onto most any glaze and get carbon trapping in the sprayed area (assuming the firing promoted carbon trapping). You can also spray this directly onto unglazed clay and get "flashing" effects that lightly resemble some wood fire or soda fire effects.

If you handle the "fuzzy" surfaced pots, any fingerprints that you migh leave likely WILL show up in the fired state... so be careful. You can USE this idea as a decorative technique.

best,

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

[armen]

JBaymore, on 24 September 2012 - 10:57 PM, said:

Carbon trapping with high soluble soda content glazes like the usual Maclom Davis shino recipe is affected greatly as a function of the firing cycle. For very heavy carbon trapping you need to start heavy reduction at a very low cone... like about cone 012. The serious carbon trap schedule is kinda' incompatible with a number of other glazes which react badly to such heavy reduction at such a low cone.

And if you did not "do the job" at bisque in order to burn out the carbonaceous materials in the clay body (had lots of oxygen in the kiln atmosphere) AND you start heavy reduction this low... expect some body related firing defects to crop up.

You can mix up a super saturated solution of soda ash and hot water until the water will not disolve any more of it..... and then spray it onto most any glaze and get carbon trapping in the sprayed area (assuming the firing promoted carbon trapping). You can also spray this directly onto unglazed clay and get "flashing" effects that lightly resemble some wood fire or soda fire effects.

If you handle the "fuzzy" surfaced pots, any fingerprints that you migh leave likely WILL show up in the fired state... so be careful. You can USE this idea as a decorative technique.

best,

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

Thank you John.
Unfortunately, I don't have control over the firing schedule since this is being done in the context of a university studio where many other people's work is being fired. I do know that IU have previously achieved carbon trapping here, so the firing schedule used is at least potentially compatible. This is why i'm concentrating on what i can do outside of the kiln. Do you have any advice on crawling, and how to prevent at least large patches of it - I'm happy with the decorative effects of crawling, but when I have large bald patches on the inside of drinking/eating vessels, it becomes impractical.

[neilestrick]

MD Shino looks best on white bodies, even porcelain. On darker bodies it tends to go a shiny metallic gold color. For good carbon trapping, give it a day or two to dry so the salts can come to the surface. Start reduction, really heavy, no later than cone 012. The thicker it is the more likely it is to crawl.

[armen]

neilestrick, on 25 September 2012 - 12:09 PM, said:

MD Shino looks best on white bodies, even porcelain. On darker bodies it tends to go a shiny metallic gold color. For good carbon trapping, give it a day or two to dry so the salts can come to the surface. Start reduction, really heavy, no later than cone 012. The thicker it is the more likely it is to crawl.

When you say, give it a day or two, do you mean, at a minimum, or at a maximum. I can glaze weeks in advance of firing. is that better, or do you mean it's best to give it a day or two and no more.

Any input on speed of drying w/ regard to crawling?

[JBaymore]

A large part of the crawling of shinos is due to a combination of the high plastic raw clay content of the glazes along with the high surface ternsion of those high alumina content glazes. It has little to do with the soda ash content or drying rate.

The glaze starts to crack up like a dry river bottom early in the firing due to the clay content, and then the surface tension of the melt prevents it from flowing back and healing over the "cracks". The little cracked "islands" pull back into themselves like water on a freshly waxed car hood balls up..... and you get the rounded-edge crawling/cracking evident in some American shinos (not Japanese shino however).

One solution to cut this down is to calcine some (or all) of the clay content to make the applied raw glaze layer shrink less in the early stages of the drying and firing process.

Take your ball clay and put it in a big bisqe bowl and fire it in a bsique. TYhe use that iunstead of the raw clay in the recipe. Because of the loss of the water content this will actually change to final fired formula.... but most shinos are forgiving enough to tolerate this withiout a huge change in the fired appearance (other than reducing the crawling).

Alternately subsitute commercial calcined kaolin for the raw kaolin.

best,

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

[JBaymore]

neilestrick, on 25 September 2012 - 01:09 PM, said:

MD Shino looks best on white bodies, even porcelain. On darker bodies it tends to go a shiny metallic gold color. For good carbon trapping, give it a day or two to dry so the salts can come to the surface. Start reduction, really heavy, no later than cone 012. The thicker it is the more likely it is to crawl.

Pop the Redart out of the Malcolm recipe and it looks far better on an iron body IMHO.

The traditional Japanese shino clay body is actually a white -ish clay (kinose) that is not well vitrified at all. And Japanese shino and American shino are two VERY different beasts. They look very different. Note that "carbon trap" in such glazes is generally looked at as a defect in Japan....although now some of the younger generation there are looking at what Americans are doing and like it.

Japanese shino contains no soda ash and no spodumene. (The early Wirt development using spodumene and the early circulation of that glaze information lead the American shino development onto a very different path from the actual Japanese approach.) In fact, the Japanese glaze is, for the most part, a single feldspathic type rock. Sometimes up to 10% of a kaolin-like clay is added to the ground rock, depending on the potter. Some potters also use a seaweed emulsion as a suspender/binder... and hence there might be a tiny tad of sodium in there from the salt contamination in the seaweed.

The Japanese variety is fired to a much lower end point temperature than American Shino.....but over a very extended firing cycle...... (some of my friends there fire for 70 to 120 hours) so the heat work is still about cone 8. The key to this material there and the "look" is that the rock is crushed via a stamper mill. The particles have sharp edges, not the rounded grains of the usual western industrially processed Neph. Sy or feldspar materials. This helps the glaze fuse in the intial stages of the firng as the overlapping edges sinter.

I occasionally ship home small amounts of the shino rock from Japan to use here.

best,

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

[armen]

JBaymore, on 25 September 2012 - 02:58 PM, said:

I occasionally ship home small amounts of the shino rock from Japan to use here.

Shino rock. Amazing term. As a student, it's still hard for me to imagine that it's just rock that makes up my glazes.

[JBaymore]

armen, on 25 September 2012 - 05:07 PM, said:

Shino rock. Amazing term. As a student, it's still hard for me to imagine that it's just rock that makes up my glazes.

The "Mashiko Kaki" (persimmon red) glaze made famous by Hamada Shoji is a single ground stone also. As you can image in when mixed up as a glaze.... it settles...... "like a rock". 'Cause it is.

Yeah... we often forget that ceramics is "born of earth and fire".

If you fire to cone 8-10 range, go dig up some non-humus (low organic content) earth/dirt and seive it through an 80 mesh screen. Mix it about 50 / 50 with some seived common wood ash. Put it on a pot and fire it. Likely you'll have a "glaze" of some sort.

best,

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