White and blue

[Jminahan]

Hello I'm new to using anything other than store bought glaze. An old friend gave me some bags of cobalt oxide used for Delftware but didn't tell me how much powder for how much water. I was hoping someone could tell me where a good starting point is for experimentation. 

[Hulk]

Hi J!

Cobalt is a powerful colorant; my bluest glaze calls for 1.6% (by weight) Cobalt Carbonate.
Cobalt Oxide is somewhat stronger than the Carbonate form - less weight is required to achieve the same color concentration.

Perhaps you are looking to wash or stain, then glaze over?
There are some recipes/guidelines for preparation and use of washes here somewhere. Check out Mark's bowls:
Lettering a marriage crock - Studio Operations and Making Work - Ceramic Arts Daily Community
You might try some test tiles afore marking up something you are/were invested in.

...any road, be careful with that stuff! It's expensive, and it's a metal as well.
I don't remember which version is more soluble. Try not to breathe or eat it, and careful handling it - it might show up down the road, heh, a little can go a long way.
For sure avoid the fumes from the kiln.

 

[Jminahan]

Hi and thank you for responding. I was told that a little goes a very long way but I never was told how little. And I was also planning on some test tiles but I was hoping to do as little experimentation as possible so your first answer is great to hear and I'll start around there. Thank you so much. 

[Callie Beller Diesel]

You can get a nice soft blue with as little as a tenth of a percent in a glaze. 1% will often get a dark, opaque blue.

[oldlady]

do you know the size of the bags?   cobalt oxide is one of the most expensive colorants there is.   if the bags are unopened maybe you can trade them for a lot of other colors, there are lots of potters in the LA area.  check local prices at your dealer.

[Jminahan]

Edit- Turns out I have a small bad of cobalt oxide and a small bag of cobalt carbonate. 

I made a small jar of each with water. I'm trying the carbonate first which is about .9 percent by mass and while it is pink coloured it is still clear on the brush and on whatever I try to glaze. Is it supposed to be like this or should I put more in?

 

[Callie Beller Diesel]

If you’re painting with diluted cobalt, it’s easier to see what you’re doing if you use the oxide instead of the carbonate. Carbonate will still be a very powerful colourant, but you’ve already noticed it’s hard to see how it layers.

If you use the oxide, it behaves a bit like India ink, and you can see the shading a bit better. 

[oldlady]

thanks, callie, it sounds like you are suggesting something like a wash.   i have some of the oxide but did not like it in a glaze because of the tiny specks.   does it do that in a wash?

[Jminahan]

I hope this isn't a stupid follow up question but I couldn't find anything online about what to dilute it with. I was originally told to just put it in water and I'm good to go. Am I supposed to mix it with like clear glaze or something. And yes I was planning on going over it with clear after. 

[Babs]

What size of Jar, what size of bag???

I would make a test plate and make a number of dilutions and brush a strip of each on tile number jars and number brushmarks accordingly.

[oldlady]

what you use names the result.   if you put it into water, use distilled if possible, you will have what is called a "wash".   if you add it to clear glaze you will wind up with blue glaze.   if you add it to clay that has been watered down to a liquid, you have a slip.    now you just have to learn what to use when.   there is a never ending learning curve with clay.

if you get some good books from your library, you will learn a whole lot in a short time.   there are lots of them.  look here on the forums for a list.

[Jminahan]

I put about two ml of carbonate and 200 ml of water. I used simple tap water so later I'll go out and get some distilled. I was hoping to get it to act like watercolour but I think mixing it will clear glaze and water will get me the result I'm looking for. 

[Min]

You might find smudging to be an issue so be careful handling the pots. During firing the carbonate will turn into cobalt oxide. I've found that cobalt carb smudges more when dry than cobalt oxide, maybe try both. Do you have any iron oxide? Adding a little of that and or manganese dioxide will tone down the cobalt if you find straight cobalt alone too harsh. Either way keep it well stirred while using it. Covering glaze will make a difference as to whether the brushwork will bleed or run into the glaze. I would suggest trying some brushwork on both greenware and bisque tests.

[oldlady]

"with clear glaze and water"?   is the clear glaze a powder that you usually mix with water or are you using a wet clear glaze and adding water plus cobalt?   sorry, i am over my head since you are not using grams for the powdered cobalt.   it sounds like equal amounts to me which will make an extremely dark cobalt blue.

[Jminahan]

The clear glaze is wet glaze that I water down to use to fill other vessels because it is thinner and easy to put in with a funnel.  I am basically only using one percent cobalt and the rest either just water or clear glaze.

[Babs]

Depending onthe glaze your lines may end ip moving on your pots