Is tradicional chinese porcelain painted with pure oxides?

[thiamant]

Hello!

I have seen these videos of chinese people painting porcelain. I see very often they have a mortar containing what it looks pure cobalt oxide. I have always heard that you should mix your oxides / stains with a flux to avoid shivering and other problems. 

Do they use pure oxides or also mix with flux? How different is the result from using a commercial underglaze?

[Mark C.]

You can mix cobalt with water (no flux) and paint it on and put a clear glaze over .Many oxides are the same as long as a clear is over the top. They do not need fluxes.

[Min]

Japanese and Chinese cobalt brushwork was traditionally done with impure cobalt pebbles called gosu. Bernard Leach made up a mixture to approximate the colour as Manganese dioxide 40 + Black Iron Oxide 30 + Cobalt Oxide 20 + Calcined Ochre 10. Having the manganese, iron and ochre in the mix tones down the cobalt. I have found some oxides will cause the covering glaze to crawl away, trial and error. (aka, test, test, test) 
 

[thiamant]

43 minutes ago, Min said:

Japanese and Chinese cobalt brushwork was traditionally done with impure cobalt pebbles called gosu. Bernard Leach made up a mixture to approximate the colour as Manganese dioxide 40 + Black Iron Oxide 30 + Cobalt Oxide 20 + Calcined Ochre 10. Having the manganese, iron and ochre in the mix tones down the cobalt. I have found some oxides will cause the covering glaze to crawl away, trial and error. (aka, test, test, test) 
 

Oh so thats why it is called gosu painting in Japanese? I think its written as 呉須

So what did you do to fix your problem? Changed proportions or glaze itself? 

Is it possible to draw fine lines without adding anything else to the mixture? 

[oldlady]

seth cardew gave a workshop years ago.  of course, he did the fabulous bird plate done by his father, michael.   he used a simple wash of cobalt for the blue and red iron oxide for the brown.  nothing but oxide and water, skill and experience.   i have the plate he did in that workshop.  if you have never seen one of them, you have missed out.   they are in books and i am sure somewhere on the internet.

[Callie Beller Diesel]

It appears just to be mad painting skills on the part of the decorators. Good brushes, well ground pigment, and a LOT of practice.

[Jeff Longtin]

A young coworker is an art history major. (with a ceramics minor) She told me her final paper was on this very subject, "Chinese porcelain." She explained that research suggests that the Chinese potters pre fired their cobalt oxide. They placed it in the front chamber, the cooler chamber, and fired it, thereby turning it into cobalt carbonate. We have both in the studio, so I'm aware of their physical differences, (pink vs blue/black) and aware that carbonate is slightly less effective, but not sure why they would have done this? (I've not had a chance to discuss THAT aspect with my coworker.)

[Babs]

22 hours ago, Jeff Longtin said:

A young coworker is an art history major. (with a ceramics minor) She told me her final paper was on this very subject, "Chinese porcelain." She explained that research suggests that the Chinese potters pre fired their cobalt oxide. They placed it in the front chamber, the cooler chamber, and fired it, thereby turning it into cobalt carbonate. We have both in the studio, so I'm aware of their physical differences, (pink vs blue/black) and aware that carbonate is slightly less effective, but not sure why they would have done this? (I've not had a chance to discuss THAT aspect with my coworker.)

Maybe less intensity of colour  therefore easier to control the intensity.

The chemistry on burning cobalt oxide and ending with CoCO3 I'd like someone to go through....

[Hulk]

From Tony Hansen's site: "The carbonate is produced from a liquid reaction between cobalt II acetate and sodium carbonate to produce red violet crystals that are recovered by filtration. The material is insoluble in cold water but will decompose in hot water."

A bit of math to determine which gets more blue per dollar (oxide or carbonate) - which I skipped, as the carbonate form may be less prone to spotting, due to smaller particle size (typically).

Perhaps Jeff's coworker was referring to roasting cobalt oxide to get the less dense oxide?

From Tom Buck's clayart (pottery.org) entry on the subject*.

"Cobalt forms two oxides: Cobalt (II) Oxide, CoO; and Cobalt (III)
Oxide, Co2O3. But the producers likely ship a mixture of both.
Cobalt (II) Oxide is made by "roasting" the Carbonate Basic compound,
and the result is a greyish powder that is quite dense (6.4 g/mL) with very
high melting point (1935 oC). This insoluble material is supplied in two
grades, technical and ceramic. It has several uses aside from pottery.
The other oxide, Co2O3, is a steel-grey or black powder, density
4.8 g/mL, insoluble in water. It changes to CoO at 895 oC. It is made from
other cobalt compounds by heating them at low temperature with excess air.
It is used chiefly as a pigment and an enamel/glaze colourant."

*Well worth reading and re-reading! A take-away bein' that the material we're getting is very likely a mixture, hence significant variance is possible - more or less bluing from same weight o' colourant - hence II, test test test. clayart - thread 'cobalt and cobalt carbonate' (potters.org)

 

[Babs]

 

@Hulk

Or what was witnessed was the roasting ofcthe carbonate to get cobalt oxide

From above
"Cobalt (II) Oxide is made by "roasting" the Carbonate"

[Hulk]

Aye, was guessing the potters in question didn't have the carbonate form to start with.

[Babs]

@Hulk

Or had a rock source out of which the roasting of produced the co oxide