Cobalt Wash

[Chilly]

Cobalt wash

I’ve bought some Cobalt Oxide and want to use it to give a graduating colour on a mug.  Darker at the top, lighter at the bottom.  ^04 bisque and ^6 glaze fire.

I've spent ages researching, and have found loads of info, the but the following comment seems the most helpful.

“They must be applied over (not under) a glaze for successful results. Application of oxide washes under a glaze often results in areas of 'crawling,' in which the glaze pulls back to reveal the clay underneath. Chrome oxide and cobalt oxide are especially likely to cause galze crawling when applied under a glaze.†From here: http://seco.glendale.edu/~rkibler/oxidepainting.html. with no recipe or instructions given for making the “washâ€.

 

I also found reference to adding a “flux†to the cobalt.

 

Has anyone any experience with using a wash?  Over or under a glaze, and should that be over a clear or white or ??? colour glaze. 

 

I'm going to test, test, test, but I need a starting point as we only do two bisque and two glaze fires a month, if that. 

 

How does this sound for test tiles for starters?

 

1.     Clear glaze with 1/2/3 coats Cobalt/water over

2.     White glaze with 1/2/3 coats Cobalt/water over

3.     No glaze with 1/2/3 coats Cobalt/water

4.     No glaze with 1/2/3 coats Cobalt/neph sy/water over

 

Any other suggestions gratefully received.

[High Bridge Pottery]

I have this recipe for a blue wash, never tried it but I have had success mixing my clay with 0-10% cobalt to make a coloured slip, don't know if that is classed as a wash.

Blue
Red clay 100g
Cobalt oxide 4g
Manganese Dioxide 4g
Water ~
Enough water to make it into a watercolor consistency. The iron in the red clay and the manganese soften the harsh blue that you can sometimes get using the Cobalt alone.

Also this one, I am sure you could try without the manganese dioxide.
Grey Blue
Cobalt Carbonate 60
Manganese Dioxide 20
Gerstly Borate 20

 

Underneath are my tests with Cobalt Carbonate 1%, 2%, 4%, 8%, 16% and 24% with the clay body. It is under a white glaze.

[Rebekah Krieger]

these are mugs I used a pre made cobalt oxide wash. It was applied to bisque and the amaco clear glaze (mid fire) was applied over it.  I did not have trouble with crawling but I did use commercial wash... maybe that makes a difference? I plan to make my own wash soon 

[rayaldridge]

You might consider spraying the wash on with a mouth atomizer.

[Chantay]

The Complete Guide to Mid Range Glazes has a reciepe for a wash using yellow ochre.  You could use the same and substitue the cobalt. 

 

Yellow Ochre   33.33

Kaolin              33.33

Frit 3124          33.33

 

It also states:  "Washes are coloring oxides combined with a flux and mixed with water, usually in a 50/50 blend.....most potters just measure them with a spoon." 

 

Copper Wash 1

 

1 teaspoon copper carbonate (or Mason stain)

1 teaspoon Frith 3110 (or Gerstley borate)

 

 

Copper Wash 2

 

1 teaspoon copper carbonate

1 teaspoon frit 3110

1 teaspoon EPK

 

 

[bciskepottery]

Cobalt wash

I’ve bought some Cobalt Oxide and want to use it to give a graduating colour on a mug.  Darker at the top, lighter at the bottom.  ^04 bisque and ^6 glaze fire.

I've spent ages researching, and have found loads of info, the but the following comment seems the most helpful.

“They must be applied over (not under) a glaze for successful results. Application of oxide washes under a glaze often results in areas of 'crawling,' in which the glaze pulls back to reveal the clay underneath. Chrome oxide and cobalt oxide are especially likely to cause galze crawling when applied under a glaze.†From here: http://seco.glendale.edu/~rkibler/oxidepainting.html. with no recipe or instructions given for making the “washâ€.

I also found reference to adding a “flux†to the cobalt.

When you apply an oxide wash on bisque, the oxide usually dries like a fine powder on the surface of the bisque (and smudges quite nicely). When you apply glaze over that oxide dust, the oxide acts the same as any type of dust or dirt that prevents the glaze from adhering . . . so the glaze tends to crawl because of the dirty surface. Applying just an oxide/water wash to greenware does not help as much as the bisque temperature is not high enough to melt/fuse the oxide to the clay body -- which is why oxides tend to remain powdery after bisque. Adding the flux to the oxide wash lowers the melting point so the wash adheres during a bisque firing. Lessons learned from experiences with RIO.

 

Cobalt is a strong colorant . . . so getting variations is going to be hard without adding something to the cobalt to soften the color. Maybe try some combinations of cobalt and rutile or cobalt and tin oxide/zircopax, etc.

 

Unless you are wedded to using cobalt, it might be easier to get gradients by using a series of blue mason stains or equivalent stains to get the progression you are looking for.

[oldlady]

cobalt oxide sometimes leaves tiny blackish specks because it needs grinding in a ball mill.

 

cobalt carbonate is not as strong but it makes very dark blues even at only 1 1/2%.  if you are trying for an ombre effect, you might try bruce's suggestion of a stain.  i know mason stains are very expensive in the UK.  mason stains are so common here in the states we forget that there may not be anything comparable for you to use.  still, there must be something available in Europe or we would not be seeing blue Polish Pottery advertised everywhere.  what kinds of stains are available?

 

(Evelyne is coming to Nceca in march, is it cheaper if she mails something from Switzerland?  or would that be illegal?)