Calcining Cobalt Carbonate

[Soren]

Is it possible to calcine Cobalt Carbonate into Cobalt Oxide?  Is that how Cobalt Oxide is usually produced?

If so, how should I go about calcining the Cobalt Carbonate?  Is this hazardous to do in a simple shop environment?  What cone should I use to properly calcine the Cobalt Carbonate?  How should I contain the powder during calcining?  Should I even consider trying this myself with limited experience?

I purchased a pound of Cobalt Carbonate that produces a medium blue rather than the desired dark blue when I mix it into my clay body.  If I could calcine this into Cobalt Oxide in order to obtain a darker blue, I might be able to gain value and avoid having spent money on a product without my desired intent.

Thanks for any calcining advice!

Kind Regards,

Soren

[Callie Beller Diesel]

If you're looking to save money, a body stain will be cheaper than using either oxide or carbonate. 

[Soren]

1 minute ago, Callie Beller Diesel said:

If you're looking to save money, a body stain will be cheaper than using either oxide or carbonate. 

Can you recommend a body stain to use to obtain a dark navy blue with Amaco Versa Clay #20 earthenware?  My experience so far with stains has not achieved dark coloration I would like.  I have tried Mason Stain 6300 Mazerine up to a ratio of 10 clay to 3 stain (23% stain), and the color is still only medium blue bisque fired to cone 04.

Cost is not my only concern.  If I can pay more to achieve the dark blue clay body I would like, I am willing to do so.

[neilestrick]

The carbonate turns to oxide during the firing, so starting with one vs the other won't change the outcome. Oxide is stronger by weight, so you can just use more carbonate to get the same effect. If you want the cobalt darker, try adding some iron to it.

[Soren]

24 minutes ago, neilestrick said:

If you want the cobalt darker, try adding some iron to it.

Thanks for the recommendation, Neil.  I will try adding some iron.  Would this also work to achieve a darker blue if I add cobalt carbonate to a terra cotta earthenware that is orange in color (due to added iron, i think?)?  This was a test I planned to try but have not done so yet.

If cobalt oxide is cobalt carbonate that is calcined (whether as powder or in a glaze or clay body), is the oxide stronger since all water has been driven off, meaning more stain mass for the same total powder weight?

[neilestrick]

5 minutes ago, Soren said:

Thanks for the recommendation, Neil.  I will try adding some iron.  Would this also work to achieve a darker blue if I add cobalt carbonate to a terra cotta earthenware that is orange in color (due to added iron, i think?)?  This was a test I planned to try but have not done so yet.

If cobalt oxide is cobalt carbonate that is calcined (whether as powder or in a glaze or clay body), is the oxide stronger since all water has been driven off, meaning more stain mass for the same total powder weight?

I think in a terra cotta it will just go black. To much iron.

Yes, the oxide is stronger by weight.

[Soren]

2 minutes ago, neilestrick said:

I think in a terra cotta it will just go black. To much iron.

I am also trying to obtain a good clay that fires to true black at cone 04, so this might be a good option for that.

Thank you very much for your advice!

[dhPotter]

My understanding of copper or cobalt carbonates is they have an extra Oxygen molecule. 1.5g carbonate  =  1g oxide.

[glazenerd]

DH: our beloved Feds actually have laws on the books regarding certain chemicals sold to the public. Lithium for example can only be sold publicly in a carbonated form: maximum oxide 40% and 60% carbon(ate) fluff: that burns off. Not certain, but i am thinking this also applies to other oxides. Flouspar can only be sold in acid grade. 

Calcining cobalt carb. Is a bad idea: over fire it and you will have a nice blob.

In crystalline glaze: the trio always produces dark blue/ black. 3% each of cobalt! iron! and manganese. For a clay body: start with 1% cobalt carb just to give the body a blue hue. Then you need much less blue body stain to get the color you want. You can start with 1% cobalt and manganese to deepen the body color! then use even less stains. Remember, there are " body stains" specifically made for clay colorants. You will use much more "regular" stains to achieve the same color, plus the fact the chemistry is a bit different.

giving away formulation secrets again.   Someone shoot me.

t

 

 

[Soren]

Thanks for the information, glazenerd.

I have a few questions for you:

29 minutes ago, glazenerd said:

Calcining cobalt carb. Is a bad idea: over fire it and you will have a nice blob.

What level would be overfiring?  When I last tested, I wiped up some spilled cobalt carbonate powder and poured it onto a small scrap disk of clay (same clay as body I want to stain).  After bisque firing to cone 04 with the other test disks, the powder turned a nice dark blue, but much of it remained powder on the surface of the disk that easily brushed off.  Would this likely work the same if I tried to calcine the cobalt carbonate?

I am suspecting now that the best route is in your next suggestion, which does not require any calcining on my part:

31 minutes ago, glazenerd said:

In crystalline glaze: the trio always produces dark blue/ black. 3% each of cobalt! iron! and manganese.

This trio is definitely something I will try with my clay body.

32 minutes ago, glazenerd said:

For a clay body: start with 1% cobalt carb just to give the body a blue hue. Then you need much less blue body stain to get the color you want. You can start with 1% cobalt and manganese to deepen the body color! then use even less stains.

I am not clear on what you mean here.  Is this if I use stains in conjunction with oxides?  So, 1% cobalt carbonate and some percentage Mason Stain, which requires less stain to obtain blue?  ...and 1% cobalt carbonate with 1% manganese paired with stains to achieve darker blue?  I have manganese on order right now to help deepen the color, but I am trying for blue right now with just oxides.  With the stains and oxides I have, I certainly plan to experiment with different combinations to develop the colors I would like.

35 minutes ago, glazenerd said:

Remember, there are " body stains" specifically made for clay colorants. You will use much more "regular" stains to achieve the same color, plus the fact the chemistry is a bit different.

How do I note the difference when ordering stains?  I think I have seen this sometimes, but I will pay more attention to this in the future.  Do you know how I might learn more about the chemistry involved with body stains versus slip/engobe or glaze stains?  With my lack of experience, I assumed the difference was mostly how much stain was visible on the surface, either through concentration or transparency of the carrier; I was completely ignorant of the chemical difference.

I am not asking anyone to share formulation secrets, but I do thank anyone who can help me get started with coloring clay.  The level to which I am delving may be a bit much with my limited ceramic hobby experience, but the science is a fascination to me, since I am an engineer by trade.

[Fred Sweet]

Soren-

Check Chris Campbell’s website:

http://www.ccpottery.com/coloredclaylessons.html

This is her colored clay tutorial/class page. You might find your answers there. She is often approachable via email, depending on her schedule.

She is also a member of this forum and has a gallery here. Go to the main page and do a search on her name. 

Regards,

Fred

[Soren]

25 minutes ago, Fred Sweet said:

Check Chris Campbell’s website:

Fred, thanks for the recommendation.  This happens to be one of the same references I used to get started with coloring clay.  This reference is what has made me question my process or body clay, as I am getting pastel colors with concentrations around 20% color to body clay for both oxides and stains, which is much higher than the recipes Chris shows on her site.

This holds particularly true for my cobalt carbonate tests.  At a ratio of 10 clay to 2 cobalt carbonate (16.67% color), the resulting color is only medium blue, not the dark blue I had intended to achieve.  (Body clay is Amaco Versa Clay #20, which is dark gray wet, light gray dry, and white fired to cone 04)

I will have to try to learn more from Chris and from others with experience in this area, as I am a complete beginner with stains and oxides (not to mention generally inexperienced with ceramics in general).

[glazenerd]

Soren:

The Mason Stain website has a filter selection on its main page: just click it and select " body stains" and hit apply.

http://www.masoncolor.com/ceramic-stains

Use oxide colorants to ( cobalt, iron, and copper) to create the basic hue in a clay body. 1% cobalt for example to create a light blue body. Then use a blue body stain  to create the depth of color. Yes, you are using them in conjunction: the oxides create color at much lower % than an equal amount of stain. Black for example: 3% red iron and 5% black stain creates a much richer black than 8-10% black stain. For blue: start with 1% cobalt, 2% manganese: then 3-5% blue body stain. 

Mix test batches in 500 gram increments: assuming you are starting with dry clay recipes?

if not, then start with 600 grams moist clay, less 20% water weight = 480 grams dry weight. Keep detailed notes on the % of oxide/ body stains used to create each color. Unlike glaze, increase in 10% increments from batch to batch. EX. If first batch has 5 grams cobalt and 25 grams body colorant in 500 grams: the next batch would have 5.5 grams of cobalt and 27.5% body stain. Glaze takes little to move the color needle, clay takes much more.

clay has 20% moisture content and remains in the plastic limit index. ( Atterberg Limits.) slips run 40% water content! and fall in the Liquid Limits (LL) and engobes run 30-32% water content and are also in the LL (liquid limits). 

Tom

[Fred Sweet]

Soren-

Most body colors will develop their true intensity with the addition of a clear glaze. To get an idea of how it will look prior to glazing and firing the work put a drop of water on the surface. While it won’t be highly accurate, you will get an understanding of just how the glaze will influence the color development.

Regards,

Fred

[Callie Beller Diesel]

Soren, I'm sorry, I'm late to the party. Others have supplied the answers I would have to your question. 

With regards to the intensity of colour you're getting compared to Chris: it should be noted that Chris works with porcelain. Translucency will be a factor.

[Soren]

Thanks for all the information, Tom!  As a complete beginner, I know I still have much experimentation ahead to develop the colored clays I would like.  These tips are certainly a boost to me to help this process.

15 hours ago, glazenerd said:

The Mason Stain website has a filter selection on its main page: just click it and select " body stains" and hit apply.

That should help a lot.  It is also nice to see that the 6300 Mazerine I have is a body stain.

I am using wet clay right now, as all mixing is done by hand.  At this point, I do not have a ball mill or pug mill, and I will probably not be getting this equipment, as it is not cost effective for a hobby ceramicist like me.  Working by hand is good enough for me, as it is a great break from sitting at a computer for work.

Thanks for the numbers on water content and the color test tips.  I am currently testing colors and keeping notes on concentrations, but I have been testing with ratios rather than true percentages in order to keep the numbers simple.  I label the test disks with a number that denotes the ratio compared to 100 of clay, so a disk labeled "20" was mixed at a ratio of 20 parts stain or oxide powder to 100 parts wet clay.  I initially tested all stains and oxides at ratios of 10, 5, and 1 colorant to 100 wet clay to see the shade variations.  At this point, I have not had the time to mix different stains and oxides, but that is the next step after developing the base palette.  I asked this question now to determine if there might be a better clay both for coloring and for my working purposes before I spend many hours on experimentation and too much cost on stains and oxides.

11 hours ago, Fred Sweet said:

To get an idea of how it will look prior to glazing and firing the work put a drop of water on the surface.

Thanks for the tip, Fred!  I will keep this in mind.

10 hours ago, Callie Beller Diesel said:

With regards to the intensity of colour you're getting compared to Chris: it should be noted that Chris works with porcelain. Translucency will be a factor.

Thanks for confirming this, Callie.  I suspected Chris worked with porcelain with greater translucency that would require less colorant for darker shades.

The knowledge base in this community has been and will be a great help, especially to a hobby ceramicist like myself who has little time to do extensive and complete research and experimentation!  I am amazed at the quick and complete responses to my questions that help steer me in the right direction!