Cobalt carbonate majolica technique troubleshooting

[Hundy]

Hello!

I've been wanting to recreate the Portuguese Azulejos blue tile technique and have hit a brick wall in terms of my test tiles.  The results are blotchy and somewhat faded with diffused rather than sharp edges, almost like how tattoos are after years of sun damage. I am new to this in general, so I'm hoping someone could tell me where I might be going wrong. I have had a look at the other threads related to this and saw some sage advice for the OPs. 

Steps taken:

I made some tiles using B17C Stoneware clay from Bath Potters Supplies . The studio then did a bisque fire.

I then dip-glazed them with Stoneware Shiny White BP22P powder glaze and let it dry 24 hours. 

I then painted some designs with Cobalt carbonate powder mixed with water on the first test tile and added some gum arabic to the pigment mix on the second decorative test tile(I had seen a ceramicist recommend this addition in a YouTube video).  I tried 3 different ratios of cobalt carbonate with water; 1:3, 1:6 and 1:10 to have dark, medium and light hues.
 

The studio fired it for me at 1260° c according to the underglaze label instructions. Finally, the reason I'm doing it this way was following the methodology of an online course. 

Thank you.

Pictures:



Test 1: Only cobalt carbonate and water in varying ratios

Test 2: Cobalt carbonate and a drop of gum arabica to the pigment mix.

Edited September 12 by Hundy
typo

[Mark C.]

I think you are diluting the carbanate to much with water and gum

What is the purpose of the gum???

[Hundy]

Thanks Mark. Interesting, what ratios do you recommend? I've seen your fantastic work in other threads using cobalt pencil and also via brush, so you've obviously cracked the code a long time ago. 

  On the course videos the teacher did a 50:50 mix(this didn't have enough water to make it soluble), a 10% pigment to 90% water and a 30% pigment to 70% water.  These were all eyeballed though from experience I guess, where as I was pipetting and weighing being new to this.  I think I found online sources to suggest 1:3, 1:6 and 1:10 which is what I went with in the end.

I believe the gum arabica acts as a binder making it easier to apply with the brush keeping the pigment together in suspension more rather than agitating the mix all the time(though I did stir it up well before each stroke).  The course recommended adding a flux. I could experiment with quantities but the first test tile was still hazy-looking without any gum arabic. Makes me think it might user error on my part most likely, firing incorrectly or too high etc etc. 

 

[Mark C.]

This may sound strange to you but I have no code or formula . I just dump some carbanate in a jar and add a bit of water until it feels/looks right. No measuring. I never measure  homemade stains its always by feel no matter if its  coblat ,rutile or Iron. I do stir it up constantly and never add a flux or gum. My thought is  its one more thing to burn out and make for crawing . If you add flux that can also make the drawing move more and get blurred is also my take. Once dry I glaze with a very thin clear glaze and fire hot (I'm a cone 10 potter) . Using the right brush is also a key point

[Rae Reich]

If you have a stable base glaze, and you should for this work, you can experiment with mixing some of it in the cobalt carbonate/water mix. It won’t be as extreme as adding a flux alone and, for me, stabilizes the colorant for clear brushwork.

If you make your own glaze, leave out the whitener for this decorating use to have a more intense color. 

Edited September 13 by Rae Reich

[Bill Kielb]

On 9/12/2024 at 11:35 AM, Hundy said:

then painted some designs with Cobalt carbonate powder mixed with water on the first test tile and added some gum arabic to the pigment mix on the second decorative test tile(I had seen a ceramicist recommend this addition in a YouTube video).  I tried 3 different ratios of cobalt carbonate with water; 1:3, 1:6 and 1:10 to have dark, medium and light hues.

Just to bring up a possibility - this may be done with regular underglazes with a bit more control in a wysiwyg manner and less worry of leaching. Especially for those with elevated brush skills. Example wash decorated ware below thrown by me and decorated by M. Grant under Madison pottery collaboration.

 

Edited September 14 by Bill Kielb

[quampegan]

I’m interested in this topic as I am trying to recreate delft-like historical pieces. I am also using CoCO3 and wondered if you found a solution?

[High Bridge Pottery]

Delft seem to be earthenware, same as a lot of the spode italian stuff. They are low fired to about 1025c-1075c (1875f - 1970f) which stops any bleeding into the glaze and becoming blurred. If they are porcelain or bonechina I would guess they do a high bisque and then because the colours are oil based it doesn't need to be porous to apply the artwork or the art is overglazed after the glaze fire. All the spode blue italian I used to print was onto bisque earthenware, glazed and fired to 1050c.

Not sure how they originally did it in china on high fire porcelain but some have the blurred look.

 

Edit - I will add when they messed up the glazing and would respray and refire 2 or 3 times the artwork would start to run and blur, especially on the more vertical surfaces.

Edited Sunday at 07:19 PM by High Bridge Pottery

[Hundy]

On 9/13/2024 at 4:56 PM, Mark C. said:

This may sound strange to you but I have no code or formula . I just dump some carbanate in a jar and add a bit of water until it feels/looks right. No measuring. I never measure  homemade stains its always by feel no matter if its  coblat ,rutile or Iron. I do stir it up constantly and never add a flux or gum. My thought is  its one more thing to burn out and make for crawing . If you add flux that can also make the drawing move more and get blurred is also my take. Once dry I glaze with a very thin clear glaze and fire hot (I'm a cone 10 potter) . Using the right brush is also a key point

Thanks Mark, that's good to know. I will perhaps test the thin clear glaze that you mention. As my first tile pigment  had no additives, by a process of eliminiation I will investigate what other things might be causing the blurriness. I'm using fine liner, flat, Chinese and watercolour brushes.

[Hundy]

On 9/14/2024 at 12:01 AM, Rae Reich said:

If you have a stable base glaze, and you should for this work, you can experiment with mixing some of it in the cobalt carbonate/water mix. It won’t be as extreme as adding a flux alone and, for me, stabilizes the colorant for clear brushwork.

If you make your own glaze, leave out the whitener for this decorating use to have a more intense color. 

Thank you Rae. I was using store bought glaze as I'm still a beginner but will try and test adding it to the mix. 

[Hundy]

On 9/14/2024 at 1:32 AM, Bill Kielb said:

Just to bring up a possibility - this may be done with regular underglazes with a bit more control in a wysiwyg manner and less worry of leaching. Especially for those with elevated brush skills. Example wash decorated ware below thrown by me and decorated by M. Grant under Madison pottery collaboration.

 

Thanks Bill. That's a lovely piece and something I'd like to do in future in terms of decorating containers. The studio  I use does have underglaze paints that I could have used probably to much better effect in hindsight however as it looked almost like oil based silkscreen ink I wasn't sure how to get the different tones like in the Portuguese method with dilution. 

[Hundy]

13 hours ago, quampegan said:

I’m interested in this topic as I am trying to recreate delft-like historical pieces. I am also using CoCO3 and wondered if you found a solution?

Hi Quampegan. No not yet, but I think I'll just need to do more tests. Of course I will update if I have more success. 

[Hundy]

12 hours ago, High Bridge Pottery said:

Delft seem to be earthenware, same as a lot of the spode italian stuff. They are low fired to about 1025c-1075c (1875f - 1970f) which stops any bleeding into the glaze and becoming blurred. If they are porcelain or bonechina I would guess they do a high bisque and then because the colours are oil based it doesn't need to be porous to apply the artwork or the art is overglazed after the glaze fire. All the spode blue italian I used to print was onto bisque earthenware, glazed and fired to 1050c.

Not sure how they originally did it in china on high fire porcelain but some have the blurred look.

 

Edit - I will add when they messed up the glazing and would respray and refire 2 or 3 times the artwork would start to and blur, especially on the more vertical surfaces.

Thanks for this and your point about lower firing came up when I was searching for answers before posting here. I might try earthenware too as a test.   Also I've noticed that some of the pottery in China has a softer blurred look.

[High Bridge Pottery]

To me lower firing is certainly the easiest way to get less reaction between colour and glaze but with the wrong glaze you can still get the same look at lower temperatures too so it's not always a solution that works.

I do agree with Bill that an actual underglaze should be less reactive than pure cobalt carb/oxide and messing with the glaze chemistry (increasing silica and alumina) could also help.

 

Edit - just had a quick search about Portuguese Azulejos and they seem to be around the 1020c mark too.

Edited Monday at 03:43 PM by High Bridge Pottery

[Hundy]

31 minutes ago, High Bridge Pottery said:

To me lower firing is certainly the easiest way to get less reaction between colour and glaze but with the wrong glaze you can still get the same look at lower temperatures too so it's not always a solution that works.

I do agree with Bill that an actual underglaze should be less reactive than pure cobalt carb/oxide and messing with the glaze chemistry (increasing silica and alumina) could also help.

 

Edit - just had a quick search about Portuguese Azulejos and they seem to be around the 1020c mark too.

Do you have any recommendations on the underglaze paint? I've found something like this(https://www.bathpotters.co.uk/spectrum-cobalt-blue-537-underglaze/p2863) where the more layers applied the more opaque it becomes. I'm not sure if this will give the same effect as the dark, mid and light tones I like in Portuguese tiles.

In another thread below there is talk of adding a frit.  As far as I can make out this is powdered glass which I'm wondering if it s similar to increasing the silica that you mentioned. 

 

[High Bridge Pottery]

Don't really have anything I can recommend but I think underglaze will still give you the same dark, mid and light tones you are looking for.

 

As far as I can tell, stains are metal oxides that have been sintered with clay or some other things to make the metal oxides more stable and consistent and underglazes are stains mixed with clay, gums, frits and so on to make them nicer to use and stick to the pot better when unfired and fired. When they are talking about adding frits it's generally to help the stain/underglaze melt as they can be quite refractory, being more refractory than the base oxides is the main reason for the underglaze suggestion. You could try buying a glaze/body stain first as they should be the most refractory but they could be too dry looking if you are painting over the glaze. Hopefully that made a little bit of sense, I am not the best at explaining.

 

Edit - Just read through the thread you posted and I am in it haha, it's funny remembering how little I understood when I started my journey 

Edited Monday at 08:19 PM by High Bridge Pottery

[Babs]

Search Linda Arbuckle, she demonstrates and gives recipes for majolica techniques. Very generous with info and technique.

I do basic brush strokes on a majolica base glaze to cone 5-6

with no movemene. Your glaze chem composition is key to no movement.

[Kelly in AK]

My thought is to add clay (kaolin) to your cobalt. Shouldn’t take much to stiffen it. 

[Hundy]

22 hours ago, High Bridge Pottery said:

Don't really have anything I can recommend but I think underglaze will still give you the same dark, mid and light tones you are looking for.

 

As far as I can tell, stains are metal oxides that have been sintered with clay or some other things to make the metal oxides more stable and consistent and underglazes are stains mixed with clay, gums, frits and so on to make them nicer to use and stick to the pot better when unfired and fired. When they are talking about adding frits it's generally to help the stain/underglaze melt as they can be quite refractory, being more refractory than the base oxides is the main reason for the underglaze suggestion. You could try buying a glaze/body stain first as they should be the most refractory but they could be too dry looking if you are painting over the glaze. Hopefully that made a little bit of sense, I am not the best at explaining.

 

Edit - Just read through the thread you posted and I am in it haha, it's funny remembering how little I understood when I started my journey 

Thank you for the advice. You did a great job of explaining and it's a good thread that one. I definitely feel like I know nothing with the variety of things I've unearthed as just an addition to the cobalt like frit, flux, clay, glaze, medium, gum arabica, green tea, gerstley borate(sounds like a train station here), elmers glue etc etc. I mean it really feels like alchemy. 

[Hundy]

20 hours ago, Babs said:

Search Linda Arbuckle, she demonstrates and gives recipes for majolica techniques. Very generous with info and technique.

I do basic brush strokes on a majolica base glaze to cone 5-6

with no movemene. Your glaze chem composition is key to no movement.

Thank you Babs. I have seen her article pdf and it's great. Do you make your own glaze recipe?

[Hundy]

10 hours ago, Kelly in AK said:

My thought is to add clay (kaolin) to your cobalt. Shouldn’t take much to stiffen it. 

Thank you Kelly. Duly noted and added to the list.

[PeterH]

36 minutes ago, Hundy said:

Thank you for the advice. You did a great job of explaining and it's a good thread that one. I definitely feel like I know nothing with the variety of things I've unearthed as just an addition to the cobalt like frit, flux, clay, glaze, medium, gum arabica, green tea, gerstley borate(sounds like a train station here), elmers glue etc etc. I mean it really feels like alchemy. 

I've also read of "flat" seven-up as an alternative to green tea as a solvent/vehicle. I suppose that the sugar acts as a binder as the "ink" dries.

Edited Tuesday at 07:19 PM by PeterH

[Hundy]

43 minutes ago, PeterH said:

I've also read of "flat" seven-up as an alternative to green tea as a solvent/vehicle. I suppose that the sugar acts as a binder as the "ink" dries.

Thanks Peter, that makes it a nice round 10 things I could possibly add now. Ha!

[Babs]

If painting on glaze I wouldn't use clay  on its own incase it hinders the onglaze marrying into the glaze.  I just use cobalt and water, or for a softer blue a bit of iron. To make it painterly a tad of CMC ...

I make up my glaze from ingredients but the recipe is one of Janet de Boos's 

Google Gerry Wedd an Aussie potter, Brilliant on glaze blue decoration.

@Min can I post that here?

Some folk sinter their pieces first to harden glaze surface then decorate, some spray with starch I believe. I wpnder if spra ying  after initial paint at one strength, then paint again, spray again at a different dilution would affect anything

Edited Tuesday at 09:58 PM by Babs

[Hundy]

Interesting that you use just cobalt and water, I guess I'll need to have a go at making my own glaze down the line.

Thanks for the heads up about Gerry Wedd, I love the surf themed pots and his illustrative style.