How to achieve cloudy/smoky effect on glaze

[Julia.B]

Hi,

I am fairly new to pottery and currently experimenting a lot with designs and different glazes/underglazes (commercially bought at the moment), there is one effect I've seen in pictures a few times which I love but I don't have the first idea how to achieve it and I'm hoping someone can help explain how it is done. I've attached a picture of one example I've seen, the effect I love is the way the white on top in this picture has a cloudy/smoky translucent effect at its edges where it overlays the colour underneath, can anyone shed light on how this works?

I'll add that currently I am working with earthenware clays and I'm not sure if it is even possible in that case but any advice would be greatly appreciated.

Thanks

Julia

[Rae Reich]

This is a high-fire glaze which has a lot of rutile. Not possible to use this glaze on earthenware, but there might be something similar in cone 06 you could use. 

[Denice]

You could probably to this in earthen ware.   The bottom of the plate looks like it has a stain put on it before it was glazed. The outside and inside of the rim seems to be a opaque glaze.  The bottom has a crackle glaze on one side and translucent glaze in the middle.   You would have to do some testing it find the right glazes,  making sure they work together.   I wouldn't use this on functional work,  the crackle will allow bacteria to build in the cracks.  This will eventually make the person using it ill.    Denice

[Min]

1 hour ago, Denice said:

I wouldn't use this on functional work,  the crackle will allow bacteria to build in the cracks.  This will eventually make the person using it ill.

There was a recent study about the possible link between crazed glazes and bacteria. A study of this long believed theory was done by Ryan Coppage, PhD, Ruhan Farsin and Laura Runyen-Janecky, PhD. 

Heavily crazed glaze and a glaze with bubbles from off gassing were tested in a laboratory setting with a bacteria found in milk. All studies were repeated in triplicate with same results. 

Culture plates from bacteria laden crazed glazes that were just wiped and dried were still bacteria laden. Samples that were rinsed with water and dried with paper towels still contained bacteria but not as heavily laden. Samples that were cleaned with soap and water (and dried with paper towels) still contained bacteria. Samples from cleaning in a dishwasher had zero cultures of bacteria. With the non crazed glaze that contained off gassing bubbles (and microscopic broken open bubbles on the surface of the glaze) bacteria colonies were present after just wiping and drying but no bacteria after rinsing with water or soap and water or dishwasher.

Bottom line was the dishwasher killed all bacteria on the crazed glaze surfaces. I did note that the glazes were on porcelain, it would be interesting to see the tests done on  porous clay. Link to the article here with the test procedures explained in-depth. There is also the separate issue of crazing weakening the pot.

@Julia.B, it would take testing but I think you could get that look by using a transparent toffee coloured crackle glaze for the darker part and then a fluid off-white glaze overtop. 

[neilestrick]

I don't like glazes that are that thick and heavily crackled because I'm afraid of little flakes of glaze coming off. You can often feel the cracks in the glaze with your fingers when it's that crazed, which to me means little bits could flake off, especially with using utensils on it. As cool as that looks, I think it's a really bad choice for plates.

It looks to me like the just used the milk white glaze on the entire piece, and added a glossy crackle glaze on top of it, or vice versa. You can easily create a similar affect at any temperature by layering glazes and letting them flow together. It's all about testing to see how different glazes react with each other. Try using glazes that have different surfaces (matte vs gloss), as well as contrasting colors.

[hitchmss]

On 1/8/2019 at 1:13 PM, Min said:

I did note that the glazes were on porcelain, it would be interesting to see the tests done on  porous clay.

Min, you think the glaze would still be adhered to a porous clay body after hundreds of washing cycles? I would think the excess moisture in the clay would severely weaken the physical bond of the glaze to the clay body with repeated expansion/contraction cycles.

Interesting to see a report of bacteria in crazed glazes not being the big ol scary monster we've been preached about (at least within certain parameters.....always).

[hitchmss]

On 1/8/2019 at 3:00 PM, neilestrick said:

I don't like glazes that are that thick and heavily crackled because I'm afraid of little flakes of glaze coming off. You can often feel the cracks in the glaze with your fingers when it's that crazed, which to me means little bits could flake off, especially with using utensils on it. As cool as that looks, I think it's a really bad choice for plates.

It looks to me like the just used the milk white glaze on the entire piece, and added a glossy crackle glaze on top of it, or vice versa. You can easily create a similar affect at any temperature by layering glazes and letting them flow together. It's all about testing to see how different glazes react with each other. Try using glazes that have different surfaces (matte vs gloss), as well as contrasting colors.

Neil is right; functional ware, which has an extremely poor fit (the tighter the craze lines, the worse the fit) will flake off small pieces of glaze during use. I fire soda-lime glass into some of my work, only on pots that arent gonna be used for food/drink, or in places where it wont come into contact with food, like the lid of a butter keeper, etc. During the cooling cycle of my firing you can hear the glass crazing and if I were to take my fingers and rub over those glassy areas right after unloading from the kiln I can feel them with my nail, but here and there I'll get a little glass "splinter" which is barely visible, but hurts like heck nonetheless.

Again, I dont sell these pots with glass as utilitarian, and I tell my patrons this. I also find that most of those little "splinters" fall off after moving them around the studio a bit.

To achieve the smoky/halo effect you are interested in, find a clear glaze and try combinations of this clear glaze over/under your other glazes. What if you spray the clear onto a portion, and then spray the other glaze around it? Time consuming, but would likely produce the result you desire. Some glazes will go clear in coloration when overfired (not good), or where they are thin in their application.

Obviously, this one comes down to lots of testing, trial and error. The suggestions from other posters are good ones too. Good Luck!

[Min]

1 hour ago, hitchmss said:

Min, you think the glaze would still be adhered to a porous clay body after hundreds of washing cycles? I would think the excess moisture in the clay would severely weaken the physical bond of the glaze to the clay body with repeated expansion/contraction cycles.

I would say that it would come down to two variables, the degree of porosity / absorption plus the level of crazing. It would be interesting if the authors of the article I posted did the study with clays with a range of porosity and a quantifiable about of crazing as opposed to terms like heavily crazed. I would have liked to have seen bacteria levels after tests done on porous clays. Have you seen the image below from Tony Hansen of a  crazed glaze on a cone 6 porcelain? We don't know the absorption figures but I'm going to assume it would be low given it is porcelain, lightly tapping the mug with a spoon was enough to tear the handle off and a chunk of the interior of the clay near the rim. 

The fact that you are finding "splinters" of glass on your high coe glaze worries me. If they are splintering now aren't you concerned they will continue to do so after they've left your studio?

@Julia.B,the idea of using a transparent coloured glaze with an opaque one would be fine but like everyone has said, it would be best if it isn't crazed like the examples in your image if you are making functional ware. Earthenware has a high porosity so is prone to absorbing moisture through daily use which in itself can cause crazing, using a crazed glaze on earthenware will only exacerbate this.

 

[oldlady]

julia, i think i read your post differently.   are you really talking about the outer rim of the plate beyond the brownish spot that is crackled?   the white at the rim sort of fades to much lighter white with what looks like drips of white down toward the center.   

if that is what you are asking about, i think it is simply a poor application of glaze, not something you would want to do deliberately.   if i have misread your post, sorry, ignore me.

just discovered this post i wrote on tuesday is still here, did not hit submit until thursday at 4:22 pm.

[Magnolia Mud Research]

So far the answers seemed to be focused on the visible "crackling" of the glaze in the photograph of plates and bowl used by Julia.B to illustrate the " cloudy/smoky effect" she wants to achieve in her own glazes. 
Crackling of glaze has been a topic of debate since the beginning of modern ceramics and the discussion here seems to be sidetracked from the question asked by Julia.  

Meanwhile back to the posted question regarding the "cloudiness" of the plates. 
My experience has been  that a cloudy effect occurs when a semi-opaque glaze has been layered over an other glaze; the thicker the opaque glaze layer the less cloudy and the more pure the color of the opaque glaze becomes. 
To get the white cloud effect I would start with a clear glaze that 'fits' the clay body and add to that glaze various amounts of Zircopax to make a glaze for the  top coat.  You would have two variables to manipulate: the amount of Zircopax in the top coat, and the thickness of the top coat.  Experiments with these two variables should get you started.  

LT

 

[hitchmss]

19 hours ago, Min said:

The fact that you are finding "splinters" of glass on your high coe glaze worries me. If they are splintering now aren't you concerned they will continue to do so after they've left your studio? 

Its not my glaze that splinters. I use glass, laid into little dishes, that I expressly tell my customers arent food safe; change dishes, incense dishes, etc. It would terrify me to think that my customers would be using them to cook or eat from.

[Chilly]

3 hours ago, hitchmss said:

Its not my glaze that splinters. I use glass, laid into little dishes, that I expressly tell my customers arent food safe; change dishes, incense dishes, etc. It would terrify me to think that my customers would be using them to cook or eat from.

It terrifies me that you sell stuff that you know splinters.

I really don't understand using glass with clay.  To me it's like putting diesel in your petrol-engine car, just because they both came from crude oil.