Jump to content
Sign in to follow this  
Rex Johnson

Cobalt For Brushing Recipe?

Recommended Posts

Evidently I've had a senior moment.

It's been a while since I used RIO and Cobalt Oxide for brush decoration, maybe a couple years.

 

At any rate my RIO seems fine just mixed with water.

But my Cobalt Oxide isn't staying mixed, it just falls to the bottom, and in an hour separates and  falls to the bottom of the jar into a hard silt.

What am I doing wrong?

Should I add some clay or bentonite?

 

 

Share this post


Link to post
Share on other sites

I'm reading about cobalt carb but never used it for brushing. Doesit come out the same dark blue?

I use CO over or under white or clear.

Yes, I do use the brush t mix and go but it seems to settle quicker than I remember.

Ive also added Frit from as suggested atone other thread to make it flux better.

Maybe the frit is making it settle quicker...

 

This is an example of what I use cobalt for, simple bamboo brushing...

 

dbef36047e35daca9862758f09e8f7b1.jpg

Share this post


Link to post
Share on other sites

I use gerstley borate for my stains and oxides, and it works pretty dang well. :) I can't remember the ratio, though... I'd try one part cobalt, two parts gerstley borate. Although, I have a mason stain called Mazerine Blue that is VERY VERY cobalty (like, the powder is that weird pinkish color), and its ratio is 1:4... best make some test tiles.

Share this post


Link to post
Share on other sites

seth cardew does the kind of brushwork shown.  at his workshop, he simply mixed a little cobalt carbonate with water and stirred it often.  he did the same with RIO to get a second color.

Share this post


Link to post
Share on other sites

If you add fritt to your cobalt it will be heavier and settle out quicker as fritt is ground glass. Ger.Bor. would be a better choice. You do have to stir it constantly.

TJR.

Share this post


Link to post
Share on other sites
Guest JBaymore

Rex,

 

Man... your work there in the image looks a lot like Hamada Shoji's.  ;)

 

Hamada's slightly grey-ed out blue there is based on something called gosu... which is an impure source of cobalt.  The ground rock also contains a bit of manganese dioxide and iron oxide and some fluxing materials.  The gosu is a very fine mesh material when used for this (as well as for overglaze enamel use). The finely ground gosu powder is typically blended with a thickened mixture of a green tea extract (make strong sencha type green tea from leaves, let it sit 'forever', then boil off some of the water) that lends it brushing consistency and acts as a kind of "fixative" when it is dry.

 

For the following, note that I an working high fire.... cones 9 to 14.

 

As far a the stuff I use here in the US, I also use cobalt carbonate as the starting point of a mix rather than cobalt oxide.   Typically the carb form is a finer particle than the oxide from US suppliers.  Then to that I add a small amount of Cedar Heights Redart to add a trace of iron into the color mix, to supply a bit of flux, and to also enhance the suspension and brushability in the wet state.  Then comes a pinch of manganese dioxide for the color rendition (takes the "harsh" out of straight cobalt compounds).  Then a tiny bit of frit 3124 as more flux.  Add water.  Then I also add some glycerin to make it all brush better.

 

For the stuff that gets brushed on top over a raw glaze coating, I also add a tiny bit of white wood glue.  This causes the "dust" to set when dry and not get smudged in handling when stacking.  White wood glue burns right off and leaves no trace.  If you do this you have to keep the material in a covered container when not in use.

 

If you try this kind of mixture, to get the ratios of the coloring sources correct, you'll have to test to your own tastes in the blue you want to achieve.

 

best,

 

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

Share this post


Link to post
Share on other sites

Thanks John,

Yes that is a borrowed image. Funny I couldn't find exactly what I was looking for ;)

I have some pieces at home that are brushed over a clear cone 10 glaze that are very succesful/

I'll try and remember to take a pic.

 

I suspect having read adding flint may be the culprit as suggested.

It's completely (and quickly) separated in the jar.

 

This is probably a better example (borrowed ; ) ) ....

 

steven-smith-pottery-fish-bowl.jpg

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  

×

Important Information

By using this site, you agree to our Terms of Use.