Third Firing : What Colors To Use Over ^10 Fired But Unglazed Stoneware

[dom]

Hi all,

 

this forum has been a treasure trove of information while I was learning and exploring techniques, I hope you can help me with a specific question.

 

I like the look of unglazed clay when it has been fired at ^10. Red clays, black clays, off white clays… I like to play with the contrast of glazed and unglazed fired clay.

 

One thing I would like to try, is to give color to the unglazed areas of my work, sort of like the pitcher pic I attached below.

This is not exactly what I'm going for, though, but close. Here I assume the pattern on the unglazed clay is iron oxide applied along with the glaze and high-fired at the same time.

Perhaps the tumblers I attached are like a better example of what I'm talking about, you can see she dipped the rim in white glaze and painted the rest with bright stripes, I'm puzzled as to how/what steps/what with.

 

What I'd like to do is work in two steps. First I'd glaze the pot & fire it, and then I'd apply vivid colors to the unglazed parts, leaving the glazed part alone, and fire the ware again, at a lower temperature (lower^ is how I understand I will get the brightest colors).

 

So my question is :

 

What kind of color (overglaze/underglaze/stains..) would a) adhere to mature unglazed stoneware, and become permanent during firing ?

 

This is not for the interior of dinnerware, but possibly destined to items that would get handled a lot.

 

I guess another question would be : Am I approaching this wrong and should I consider another process?

 

Thank you for any insight you may have on this,

 

D.

 

The photos are of work by Ako Castuera and Shino Takeda 

[oldlady]

since you know who did the work, can you just ask them how it was done?

[bciskepottery]

Your difficulty in 3-times firing will be getting the lower temperature glaze to adhere to a pot that is already fired to clay body maturity, ^10, and is not absorbent anymore. Can be done, but its not easy nor reliable/consistent. Plus, reheating the glaze already on the pot could/will impact that glaze, also.

 

You can get bright colors at ^10 if you fire in oxidation. Some underglazes will hold their color to those temperatures. Others will not; it will be a matter or testing to see what work on your claybody and in your kiln.

 

The tumblers look as if the iron oxide was applied at greenware stage and bisque and then glazed in white (with a wax resist for the oxide highlight), followed by an oxide wash and/or underglaze brushed over the white glaze. If using underglazes on top of a glaze, you'll want underglazes that are less refractory and more likely to melt into the glaze for coloring. That could be one alternative to try. There are likely others, too. The fun is in solving the puzzle before you.

[neilestrick]

Ditto what has already been said. The simplest way to go is to find some underglazes that will work in cone 10 reduction and apply them during the glazing process. Apply the underglaze, wax over it and any areas you want to remain raw clay, then dip your glaze. Getting products to stick to vitrified clay can be a long tedious process with poor results, and not worth the hassle IMHO. Refiring C10 reduction pots at lower temps will often cause color shifts in the C10 glaze, so you'll have to test for that.

 

You'll have to do a lot of testing with underglazes to find some that will work. Most are made for lower temps. Many hold up fine at cone 6 (Speedball, Coyote, some Velvets), but some won't go past cone 1. Warm colors like reds and oranges tend to burn out at cone 10, and other colors may darken. Test, test, test.....If you can't get the results you want with firing C10 reduction, then consider working at cone 6 oxidation. There are a lot of beautiful C6 clay bodies.

[dom]

Hi all,

 

Thank you so much for your time and this valuable information.

I get what you are saying about issues of color holding on to vitrified clay, and oxidation modifying the color of reduction fired glazed.

Thank you for your suggestions, I'll keep experimenting and testing until I get the results I want. Or some other result, who knows? That's been a big part of the fun so far, one discovery leading to another… It seems endless!

 

Thanks again!

 

(ps, I don't know the people who made these pots, I just didn't want to post photos without crediting the artist)

[Callie Beller Diesel]

Stroke and Coat actually hold up quite well at cone 10. The reds wash out, but play with those, maybe?

[dom]

Thank you for the suggestion. I've been looking up underglazes, and so far the Amaco Velvet underglazes and Stroke and Coat stand out. I like the possibility of a matte finish with the Velvet, but the Stroke&Coat sounds more versatile.

 

The idea of getting all the decoration done in one glaze firing is very exciting, so thank you for pointing me in that direction!

[alabama]

Hey,

I have had good luck buying white plates from the thrift stores

and painting colbalt blue under glazing on them. Doc Holiday

was the mfg of the glaze. Follow directions on bottle for temperatures.

Cone 06 was what I used. I never tried it on any type of cylinder.

Experiment.

Good luck.

Alabama

[neilestrick]

Hey,

I have had good luck buying white plates from the thrift stores

and painting colbalt blue under glazing on them. Doc Holiday

was the mfg of the glaze. Follow directions on bottle for temperatures.

Cone 06 was what I used. I never tried it on any type of cylinder.

Experiment.

Good luck.

Alabama

 

Underglazes must be covered with a glaze in order to be food safe. If you're painting them on top of glaze, they should not be used in contact with food.

[rakukuku]

not sure if this is responsive but mason stains mixed with an equal amount of gherstly borrate and then water and used like water colors on bisque areas works pretty well.  some colors burn out at cone 10 but many work.   also can mix the mason stains with Leslie Ceramics stain medium instead of water.  a friend of mine used to do this a lot and paint like a water colorist using the leslie mediu.   she used to spray clear over but I don't think you have to do this.

 

i do unglazed sculptures but paint an extremely thin layer of gherstly borate and water before the cone 10 firing.  so thin you can barely see it. it gives the clay a finished look without changing color much.    rakuku

[oldlady]

looking at the pitcher makes me think that the bottom has been covered in a black slip or underglaze and the pattern is a result of cutting off some of the black.  that leaves the raw clay and the matte look of the black slip once it has been fired. it looks as though the top was dipped into white glaze being careful to stop at the point where the direction changes.

[Rae Reich]

I tested all my Mason and other stains and Velvet underglazes on various clays at ^10 on flawed bisqueware pots of each of my clays.

First, dip the bottom section in the test glaze.

Second, paint stripes of each colorant (in an order that you can keep track of) down the pot, over the raw clay and over the glaze.

Third, dip the upper section of the pot in the test glaze, being careful to leave at least 1/2" to 1" of the middle area unglazed.

Fire and label with Sharpie.

 

For consistent color application, I mix the stains (but not the Velvets) in a clear base glaze in little cups, like take-out condiment cups, labelled with the stain number. I just use the last three digits. Between firings, I let the cups dry up, to be reconstituted as needed.

 

Sometimes there is a surprising difference in the three applications. There will be a difference in the colorant's reactions to different bases, too.

 

These are fired at ^10 reduction.