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Glazing Question


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#1 sloan.quinn

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Posted 26 April 2014 - 10:41 PM

Hi all,

 

Yeah, I'm new around here. Been lurking for a while, but now I have a question.

 

Was messing around on the wheel one day, taking a break from working on a project for my ceramics class, and I came up with these. (This is after they've been fired, of course.)

 

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They're earthenware, with majolica colors on the bisqued clay (no opaque glaze), waxed over the colors then dipped in gloss black and fired at cone 04. The rims on the cups and bowl have clear glaze.

 

I am in love with the contrast in the texture and gloss, but those properties pose problems with food safety and cleaning (the texture grabs fibers from a cleaning cloth). I tried putting a thin layer of the clear glaze on the surface of the plate, but it doesn't really seem like it's sealed very well.

 

Is there a way that I could maintain at least most of that contrast without having to worry that I wouldn't be making anyone sick from the colorants/bacteria buildup? Would a matte glaze do it?

 

I'm out of access to a wheel and kiln for the summer (the university doesn't allow it unless you're registered for the class, and I can't do summer classes), so I can't really try anything until fall. All the same, I'd like to have an idea of some different things that could work.

 

Thanks a bundle!

 

Sloan



#2 Babs

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Posted 27 April 2014 - 03:57 AM

Perhaps  still use a resist to add the black but as an underglaze, bisque then wax resist the areas which you still want no shine, then clear glaze over everything at least on the food bearing surfaces

Might be one way. Babs



#3 Marcia Selsor

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Posted 27 April 2014 - 08:10 AM

Majolica colors are meant to be mixed with a glaze. Maybe try a heavier coat of clear.
..clear should be food safe.

A majolica white glaze on first then the colors on top should work..for future reference. Watch some Linda Arbuckle CAD videos.

Marcia

#4 Babs

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Posted 27 April 2014 - 05:19 PM

Missed the "Majolica colours"  bit but if you used underglaze colours at raw state as i suggested, you would get to the gloss/no gloss effect.

Marcia's suggestion is great.  L Arbuckle a treat.



#5 sloan.quinn

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Posted 27 April 2014 - 06:57 PM

Babs and Marcia, thanks for the replies. Would the underglaze maintain the contrast in the texture at all, if I did it that way? The way these are there is a wonderful change between the silky feeling of the black gloss and the roughness of the fired clay above it. Some of that roughness needs to go away to mitigate cleaning issues, I guess the "sharp" element of it, but it'd be nice if I could keep it at least a little bumpy. I've never used underglaze (I've had all of four months of instruction.) Is it kind of like slip, where you can vary the thickness?

 

Marcia, most of the work I did for class was the majolica white glaze with the colors on top, but in this case, I'm not sure I'd be able to replicate the effect...all of the yellows and browns on the pieces are just the clay. The only colors I used were the greens. Some of the upperclassmen and grad students hypothesized that the effect came from so many other glazes being in the kiln at the same time - my entire class had pieces in it, but I haven't done enough firings to know whether the effect would happen over the white glaze as well. Also, the majolica white we have makes the piece glossy - can you get/make a matte majolica glaze?

 

I did go check out some Linda Arbuckle videos, and I'll def. have to keep in mind some of her techniques for future work!

 

Thanks!

 

Sloan



#6 Babs

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Posted 27 April 2014 - 07:42 PM

Nor sure on the chemistry of underglazes v. majolica colours but I think that the M colours have at least some fluxing materials in them so they melt more easily into the underlying glaze.

The underglaze colours are not so fluxing,some are, and in fact can be used as Maj Colours.

What is the exact effect you are after

As above you could apply under glazed coloured slips, resist, apply black underglaze, bisque, apply resist, glaze with a clear, fire.

This would leave you with:

the bared areas of clay you are pursuing,

unglazed coloured areas, and

shiny black areas.

For functional ware I suggest you apply glaze to the food bearing surfaces not thinly,, sacrificing your effect for safety. Unglazed lips on mugs would have to be pretty smooth for lots of people

What effect were the grad students referring to?

Nice pots.



#7 sloan.quinn

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Posted 27 April 2014 - 10:13 PM

The grads were talking about the way the greens mellowed out some and took on quite a bit of yellow and some brown. The underlying clay bisques to a super white, and I had a couple of project pieces where the design included sections of bare clay, and they stayed white. The part that perplexed me the most was the flashes of brown streaks in places (you can see in the pics around the black glaze on the plate, and also a bit on the bowl). It was fired in an electric kiln, so it's not like there was any reduction going on to contribute to the colors changing, and these colors are usually really predictable.

 

The majolica colors we have at school are 1 pt each gerstley borate, frit 3124, and mason stain, so yeah, it's got fluxing agents in there. What you're talking about actually has me curious if the majolica colors would melt to greenware in the bisque. Any clue? Might be something to try in the fall regardless.

 

Otherwise, it sounds like the only question left is whether I can get the raised areas from the black with underglazes, or whether I'd get more texture from doing the colors before the bisque and black glaze at the same time as the clear.

 

You're really helping me think through this, not to mention giving me a bunch of ideas to play with later! Thanks!

 

Sloan

 

P.S. I had pretty much figured about the food surfaces. The last thing I want is to put someone in the hospital b/c they decided to eat their eggs off an unglazed or under-glazed (as in, not enough) plate! All the vessels are lined with the gloss black, but the plate would look weird if I just made it black. I don't think I'd go without glazing the rims on the mugs and cups, either, honestly (the light doesn't really show it, but these rims are actually glazed.)

 

P.P.S. Just an intellectual query: If I maintained the 33.3% of the total recipe for the Mason stain and reduced the amount of Gerstley borate (by a yet-to-be-determined amount), do you think the color would survive to a higher temp? Our school's recipe book specifically lists the colors as ^04, but the stains themselves are mostly listed with a max temp of 2300 F (by Mason Color). I'd really like to be able to use the colors on ^6 stoneware.






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