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BetsyLu

Underpainting With Cobalt Carbonate?

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Someone at the ceramic supply store I've been going to recently mentioned to me that it's possible to do a sort of underpainting with cobalt carbonate mixed with water. (I think...she may have said a different binder, but I'm pretty sure it was water.) 

 

I've tried researching it a little and can't seem to find anything on the internet about it or how to do it. Can you paint unfired clay with the cobalt-water mixture before you bisque it? Do you paint it on bisqueware and fire separately before glazing over top? Do you paint it on bisqueware and apply the glaze directly over the top? 

 

Would love to know if anyone has tried this and how you did it! Thanks

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Yes, you can apply to either greenware or bisque. Mix your cobalt with both a frit and water. Try the cobalt and frit in equal amounts, then add water to find the consistency and color you want. You may need to do some test tiles to find the right combination. You can also add some gum Arabic or CMC or glycerine or similar additive to make the mixture more brushable. The frit will help the cobalt adhere better. I prefer to put oxides and underglazes on greenware and then bisque; that way, if I need to touch up a color, I can do so before glazing. Others prefer to apply to bisque ware.

 

Do you dip, brush, or spray your glazes? Brushing glaze over a stain could cause bleeding. You could also apply the stain over the glaze. But, test before doing a full scale piece.

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Thanks for the info! I have been doing some more research and have read about mixing up a slip with a little cobalt carbonate in it, and then painting that on (I would assume) leather-hard clay before bisquing. 

 

I generally brush my glazes, since I don't have the equipment for spraying or the large buckets of glaze for dipping (small operation, here!) 
Sometimes I sponge on the glaze, but that takes a long time to get a good coat and since I'm doing a set of plates I will probably be brushing. 

If I apply the cobalt (either mixed with frit and water or mixed into a slip) to greenware and then fire, will it still cause bleeding? 

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As much as I love underglazes, there is something wonderful about cobalt blue decoration.

That said, one of the challenges of applying it is that it is so pale pink in the raw state that you cannot see it on the surface of your work ... you can easily smear it or smudge it and not notice until it fires incredibly BLUE.

You also have to keep your hands very clean because the smallest amount will leave a fingerprint on your work after the most delicate touch.

You could add some food coloring so you can see what you are doing.

If the pattern is complex, all around a bowl or vase or over a large area ... some people will quickly fire each section of it before continuing since hands do get tired ... who wants to waste all that work because of a small slip of the hand.

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I prefer using 40% less dark blue cobalt oxide which looks closer to how it will fire, with the added advantage of not having to fire off the carbon dioxide.

 

As much as I love underglazes, there is something wonderful about cobalt blue decoration.

That said, one of the challenges of applying it is that it is so pale pink in the raw state that you cannot see it on the surface of your work ... you can easily smear it or smudge it and not notice until it fires incredibly BLUE.

You also have to keep your hands very clean because the smallest amount will leave a fingerprint on your work after the most delicate touch.

You could add some food coloring so you can see what you are doing.

If the pattern is complex, all around a bowl or vase or over a large area ... some people will quickly fire each section of it before continuing since hands do get tired ... who wants to waste all that work because of a small slip of the hand.

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In with Norm. I prefer oxide to carb. Someone taught me to mix it in very strong green tea... Their argument was that the acid in the tea helps the mix/adherence. I'm unsure if this actually makes a difference, but I've always enjoyed the results so I've never bothered to try mixing in water.

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I use a mixture starting with black cobalt oxide that gets mortated and pestled (the black always seems to be a less fine grind than the carbonate).  To that is also added some cobalt carbonate, but far less in weight then the oxide.  To that is added a small amount of Redart clay to take off the harshness off the blue a tad by the presence of iron oxide and to improve brushing consistency.  And a small amount of frit 3124.

 

I mix it with strong green tea medium also.  (But not Matcha ;). )

 

And you can add some Elmers Glue-all (white carpenter's wood glue) to the liquid mixture to stop the dried painting medium from smudging so easily.  But if you do that, you have to keep the container of the painting medium capped most of the time and also wash out the brushes regularly.  The glue air sets.

 

A small addition of a lower melting frit will tend to "set" the bisque fired material a bit.

 

Like always... you'll have to test to find the blend that works with your clay, glaze, and style of brushwork.

 

best,

 

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

Tyler Miller likes this

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Is there anything I can trade for a frit? I don't have any as I fire cone 9/10 glazes so never needed any frits. Just want it to fuse with the pot once bisque. I bisque to 1000oc

 

Got balls clay, EPK, Feldspars and fluxes (whiting dolomite zinc etc) and gerstley borate. Not sure what that is as I use it in some recipes for suspension but after some research into oxide washes/underglazes it seems to be used in them. 

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I mix the cobalt oxide with gerstley borate, which also typically eliminates the need for adding the PVA (Elmers white) glue.

 

If you can think of a use for it you can also make a cobalt tape which is flexible and can be cut with scissors or hole punches then applied.

 

Cobalt tape uses 24 grams of PVA (polyvinyl acetate) glue (Elmers White) with 30 grams of Glycerin. You can mix this with up to 70 grams of dry material like cobalt oxide, gerstley borate or boric acid, or frit or clay.  Once it's "dry", it a flexible plastic-like wrap.  Attach it the the bisque by wetting the back side and applying.

 

Is there anything I can trade for a frit? I don't have any as I fire cone 9/10 glazes so never needed any frits. Just want it to fuse with the pot once bisque. I bisque to 1000oc

 

Got balls clay, EPK, Feldspars and fluxes (whiting dolomite zinc etc) and gerstley borate. Not sure what that is as I use it in some recipes for suspension but after some research into oxide washes/underglazes it seems to be used in them. 

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I have used cobalt ox and h2o as an under glaze on both green ware and bisque ware. I make ceramic sculpture so the blending of it with other glazes is not a problem. I worked for a potter who used it (cobalt and water) on bisque ware then dipped the work in an over glaze, the cobalt seeped through the over  glaze to create the decoration. I use mid-firing temps, she fired to cone 10.

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We make mason stain color bottles with 2/3 water and 22% gerstley borate, mixed and sieved.  To this we add 11.1% mason stain plus 5.6% zircopax for colors other than blacks or greys. The zircopax essentially gives us a white canvas to pain the bright colors on, rather than making red into a pink.  Everyone at our studio much prefers this mix to under-glazes as they never blister or change color. 

 

The clay-like properties of gerstley borate also prevent the stain from bleeding into the bisque beyond where you apply it, just as  John Baymore mentions adding PVA (white glue) to achieve the same delimiting effect.

 

Our "color  bottle" recipe results in a fairly refractory mix which, once bisque firing after applying the color, doesn't participate with or bleed into ^6 or ^06 clear cover glazes. It can be further diluted with water or brushing medium like propylene glycol or gylcerin.  Mixed one part tint bottle with 3 to 7 parts clear or white glaze results in a translucent color.

 

Making the same media above with cobalt oxide 1.8% in place of 11.1% mason stain, results in a color immediately recognizable as blue rather than the midnight blue-black achieved by mixing the same amount of cobalt oxide with brushing media. Used alone with brushing media the cobalt seems more prone to bleeding.

 

Cobalt aluminate (CoAl2O4, also sold as a Mason Color 6330) is very refractory when used alone with a brushing medium will eliminate any problems studio members have with cobalt oxide bleeding into a covering glaze - so much so, that use of cobalt aluminate over a large area can result in the over-glaze crawling away from the area covered, which some have used to interesting effect.

 

Norm

 

what ratio of cobalt oxide in Gerstley borate you find works best?

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thanks for the useful information on mixing this stuff. However, I'm a little confused about your metrics. "22% gerstley borate, mixed and sieved. To this we add 11.1% mason stain plus 5.6% zircopax "   Do I use these numbers as relative proportions of these ingredients?

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The missing ingredient I left out is water - with 100 grams of course easily measured out as 100 ml.  We use clear squeeze bottles from a restaurant supply store.

 

This is the actual mixing procedure.

 

475   $4.43   100.0%    Color Bottles - per bottle

100   $0.00     22.2%    Water

  50   $4.17     11.1%    Mason Stain  ($8.48  to  $37.50)   $4.17 average cost per bottle  

Pour above into bottle and shake

 

100   $0.17   22.2%     Gerstley Borate

200   $0.00   44.4%     Water

  25   $0.09     5.6%     Zircopax (not for Black, Grey or Taupe - but this caution has been ignored and no one noticed a difference)

 

Mix and sieve the gerstley borate base and add to each color bottle after the stain is mixed with water in the bottle.

Pour in the gerstley borate mixture leaving 1" at the top of each bottle then shake thoroughly.

 

If you mix these color concentrates with clear or white glaze in a ratio of 1 to 3, or 1 to 7, you'll quickly see that blues and greens have greater tinting power than than red and yellows.  Rather than complicate matters with a different amount of each color its respective bottle, people just get a feeling for how much to add by looking at the 1:3 and the 1:7 tiles.

 

By itself this color concentrate is slightly more fluxed than under-glaze at ^06 and not quite as fluxed as most glazes at ^6.  Gerstley borate provides needed flux and suspension in water which gives people an easy way to portion out color.

gallery_18533_676_66970.jpg

 

thanks for the useful information on mixing this stuff. However, I'm a little confused about your metrics. "22% gerstley borate, mixed and sieved. To this we add 11.1% mason stain plus 5.6% zircopax "   Do I use these numbers as relative proportions of these ingredients?

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Recently we have a veterinarian as a studio member who soon be able to make the same decisions I do. It does help a lot to have a couple of years of chemistry and science classes. He wants to make glow in the dark glazes - we haven't checked the decomposition temperatures of this material yet but it should be doable

 

 

Been done. Look up Jon Singer. Articles also in CM, if I remember correctly. He hangs out on CLAYART.

 

Jon is ceramics "tech weenie" to beat all tech weenies. Want to discuss quantum mechanics or laser exciters...... he's the guy. A pleasure to talk with.

 

best,

 

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

Norm Stuart likes this

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That's the amazing thing about ceramics.  Humans have been doing this for so long, like Chris Campbell asked - is anything original?

 

I actually emailed with Jon Singer three years ago about his results with rare earth colorants like Europeum when I was try to develop a different path to pink.  At the time I thought I understood a lot of the rare earths fluoresced under black light. But it looks like it's probably a lot of the same materials to create photo luminescence where the element absorbs light then gives it off over time as the excited electrons drop back into their lower orbitals (at least according to pre-quantum mechanics chemistry).

 

I'll hook Chris up with Jon.  It looks like a lot of overlap between these materials. 

 

http://www.jonsinger.org/jossresearch/ceramics/special/fluorphoto.html

http://www.mphotoluminescent.com/products_detail/&productId=97b071c0-080f-4f1f-88fc-60fb09147d7f&comp_stats=comp-FrontProducts_list01-004.html

http://www.gtamart.com/mart/products/phspgmnt/glaze.html

 

Thanks John.

 

 

Recently we have a veterinarian as a studio member who soon be able to make the same decisions I do. It does help a lot to have a couple of years of chemistry and science classes. He wants to make glow in the dark glazes - we haven't checked the decomposition temperatures of this material yet but it should be doable

 

 

Been done. Look up Jon Singer. Articles also in CM, if I remember correctly. He hangs out on CLAYART.

 

Jon is ceramics "tech weenie" to beat all tech weenies. Want to discuss quantum mechanics or laser exciters...... he's the guy. A pleasee to talk with.

 

best,

 

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

 

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