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Blue And White/cobalt Guru Needed!

glaze technical cobalt majolica delftware

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#1 NickiGreen

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Posted 05 February 2014 - 08:40 PM

hey all, I'm determined to work with cobalt and get detailed brush strokes on an opaque white background. I'm interested in Delftware, Chinese blue and white pottery, etc. I keep having issues with the glazes and I keep trying different ones and combos and I'm not getting anywhere. This technique/aesthetic seems so classic and universal that this shouldn't be so hard, and I shouldn't have to keep reinventing the wheel! Would anyone be able talk with me about this?

 

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Specifically, I'm using low fire majolica process for it's simplicity (i'm using this recipe: http://digitalfire.c...html?logout=yes), but the cobalt which is mixed 1:1 with non-opacified base glaze, is either chalky and almost unmelted in heavy/dark areas and in other random seeming areas the cobalt seems to bleed out onto the background. I'm looking to have relatively sharp/clean lines and brushstrokes, a more even, smooth texture (not the hard buildup in the darkest areas).

 

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I'm ready to head to Delft, NL and beg the folks at Royal Delft Blue to explain to me what they're doing. Someone, please! How is this done?

 

(p.s. don't know why CAD rotated this image, but it did. Sorry)

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#2 Norm Stuart

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Posted 05 February 2014 - 08:46 PM

1.)  You should learn to discover these problems on test tiles long before you discover them on a work of art.

 

2.)  Colorants, especially zircopax-white are very refractory.  If you add this to a perfect clear glaze it will be left unmelted to a degree, so you need to make the glaze more liquid.  With G2805 Cone 04-06 Matte, this means adding more Ferro 3134 Frit.  How much more? 

 

When testing glazes I mix them with an equal amount of water so I can measure out 20 grams of liquid glaze and know I'm dealing with 10 grams of dry glaze.  Add 0.2 grams of 3134 mix it up and apply it to a test tile.  Add 0.4 gram of 3134 mix it up and apply it to a test tile.  Some where along this line you'll leave just right and get to too much.  Mark the tiles with something like iron oxide.

 

3.)  It really is much easier to fire the ware with the Cone 6 Majolica glaze from "Mastering Cone 6 Glazes". 

 

Then decorate it with cobalt oxide, frit and bentonite - or cobalt oxide and gerstley borate and fire again at Cone 06.

 

116%   Majolica ^6

  23%   Nepheline Syenite

  23%   Ferro Frit 3124

  23%   Silica

  17%   Kaolin - EPK

  14%   Whiting - Calcium Carbonate

  16%   Zircopax  - or use 10% Tin Oxide if you're wealthy

 

This Majolica recipe will crawl back onto itself if applied too thick.



#3 bciskepottery

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Posted 05 February 2014 - 09:17 PM

The glaze crawling is likely caused by your majolica base glaze being too thick. Also, there seem to be a few pinholes in the glaze. Here is a link to Linda Arbuckle's majolica handout that talks about these problems and offers some solutions. http://lindaarbuckle...ica-handout.pdf You may find her website very helpful.

She includes a recipe for using cobalt as a colorant, too. She suggests one part cobalt, one part frit, and one-half to one part bentonite (keeps the cobalt in suspension). The frit helps to flux/melt the cobalt. I'd use Ferro Frit 3124 -- good for low fire temperatures.

There is really no need to go to Cone 6. Getting the right viscosity for the base glaze takes some time and learning; same for adding the colorants.

BTW, the carnations are beautiful; I especially like the value in the brush strokes that show gradation in color. Developing brush strokes takes time; I'm still learning after nearly 2 years of Chinese brush classes.

#4 Babs

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Posted 05 February 2014 - 11:21 PM

The glaze crawling is likely caused by your majolica base glaze being too thick. Also, there seem to be a few pinholes in the glaze. Here is a link to Linda Arbuckle's majolica handout that talks about these problems and offers some solutions. http://lindaarbuckle...ica-handout.pdf You may find her website very helpful.

She includes a recipe for using cobalt as a colorant, too. She suggests one part cobalt, one part frit, and one-half to one part bentonite (keeps the cobalt in suspension). The frit helps to flux/melt the cobalt. I'd use Ferro Frit 3124 -- good for low fire temperatures.

There is really no need to go to Cone 6. Getting the right viscosity for the base glaze takes some time and learning; same for adding the colorants.

BTW, the carnations are beautiful; I especially like the value in the brush strokes that show gradation in color. Developing brush strokes takes time; I'm still learning after nearly 2 years of Chinese brush classes.

Agree with  the above very wise man, Philosopher, bciske, no need to go to C6 , Arbuckle an authority.   Crawling may also be from fine dust etc on pot so wipe clean with vinegar water solution,

The cobalt colourant + additives should be ground and sieved, Cob Oxide gritty compared to cobalt carb. Previous post on this site somewhere was very informative. Search back a few weeks and you may discover it. No need to refire, paint onto glaze and fire as a normal glaze firing. Click on the cobalt button at top of this page and it takes you to the post I am talking about.

Google Alan Caiger-Smith majolica decoration Youtube vidoe on applying this.

Surface of the majolica glaze may need smoothing/fettling before applying your brush work. Some spray with starch to harden the surface before brushwork.

As said above read L.Arbuckle's hand out, really informative.



#5 NickiGreen

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Posted 06 February 2014 - 12:48 PM

Thanks for all of the helpful hints! Just to be clear, the "bleeding out" that I'm referring to is the blue that seems to bleed or get fuzzy into the white around the darker areas (like the banding), the sort of pocking or crawling that you're seeing at the seams is intentional and actually not crawling but just cracking in the clay body that I did not intentionally fill in with glaze. I'm brushing the base on to get a kind of gesso-y, messy aesthetic, as all of the seams are intentionally rough and cracked and messy with exposed slip connections and my intention is to have the base glaze stop in a brush stroke-like fashion before it covers the seams. Kind of like Nancy Selvin's work, but with majolica instead of matte, unglazed underglazes.

 

Does anyone know if this bleeding of the cobalt a frit issue? If seen it on other people's work before, mine just feels particularly extreme and i'm looking for sharpness. Also, the cobalt is literally blistering through the white, which is also unsightly and impractical. What do you all think?

 

Thanks again!



#6 mregecko

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Posted 06 February 2014 - 02:30 PM

Not sure if you've read this, but CAD had a nice article about maiolica including some simple glaze recipes, recipes for colorant mixes, etc:

 

http://ceramicartsda...ld-of-majolica/

 

No firsthand experience... But the article seems solid?

 

Edit: (And I just realized that CAD article has the same information linked to earlier. Oh well :-P)



#7 Babs

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Posted 06 February 2014 - 04:33 PM

the blistering is , I think, because the cobalt you are applying is still too refractory and this is why it is advised to mix with frit at the perecntage L Arbuckle and others use. The lack of sharpness may be due to the fluffiness of the glaze you are applying to or an overload of the colourant, or poss a more fliud glaze than is needed. 



#8 Marcia Selsor

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Posted 06 February 2014 - 07:52 PM

Linda Arbuckle is the majolica Queen and her handouts are great. She worked with ^6 majolica when she was in Great Britain. Mostly she works with low fire. her handouts are specific. I have followed her mixture of adding mason stains with Frit or Gerstley Borate.
Both work and give similar results.
Easy to find online or the link from Bciske.

Marcia





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