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Author: Subject: Cobalt blue (and violet and pink)
Arcaeca
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[*] posted on 29-1-2020 at 15:45
Cobalt blue (and violet and pink)


Having worked a bit with copper and iron pigments (also lead, though I never got very far), I'm thinking I want to try out some cobalt and manganese pigments. Right now I want to focus on the cobalt ones, with 3 ones in particular in mind:



  • cobalt(II) aluminate, i.e. cobalt blue
  • cobalt(II) carbonate, not sure which hydration state, but it's supposed to be pinkish
  • cobalt(II) phosphate, i.e. cobalt violet


Now the last two should just be a matter of a double displacement reaction with sodium carbonate (which you can get from putting baking soda in the oven for a couple hours) and sodium phosphate (from actual TSP sold in some hardware stores), respectively.

The first one is a bit more complicated, as the known procedure involves sintering cobalt(II) oxide with alumina in a 1:1 ratio at around 2200 F (1200 C) in the presence of oxygen. So you'd first have to prepare cobalt(II) oxide, which I assume can be done with electrolysis of cobalt metal. And if you had cobalt metal to start with, making an aqueous solution of cobalt ions for the phosphate and carbonate salts should just be a matter of letting it soak in an acid + oxidizer like aqua regia or vinegar + H2O2.

The problem right now is... where do you get cobalt?

Since most cobalt salts are poisonous, they're obviously not sitting on grocery store shelves. Cobalt(II) chloride is in found in some desiccants as a moisture indicator, but in such small proportions it's probably not worth trying to filter it out. I suppose if you had pure vitamin B12 powder and you sintered it at a high temperature you may be able to smelt some cobalt metal out, but probably a very low yield for a very high price.

The only other option I can think of is cobalt drill bits, but I'm not sure if those are just tipped in cobalt or are actually made of cobalt alloy, and if so how much impurity would need to be separated out.

What would probably be the easiest source of cobalt (in either metal or salt form)?

(Historically, btw, the source of cobalt for coloring class was mostly the mineral smaltite, although as long you're buying cobalt anyway, you might as well buy it refined...)

[Edited on 1-29-2020 by Arcaeca]

[Edited on 1-30-2020 by Arcaeca]
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Lion850
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[*] posted on 29-1-2020 at 16:04


Hi Arcaeca sounds interesting and please keep posting results. I also like to make colorful compounds. In Australia, Cobalt Oxide as well as Cobalt Carbonate are readily available from pottery supply stores. At reasonable cost. And yes, the Cobalt Carbonate I got is indeed a nice pink.

You can also get many other interesting chemicals from pottery suppliers for example Erbium Oxide and Neodymium Oxide, both elements which makes colorful salts. These are a bit more expensive though.
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DraconicAcid
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[*] posted on 29-1-2020 at 19:48


For Thenard's blue, I made a solution of sodium aluminate by reacting aluminum with sodium hydroxide solution. I added a solution of cobalt(II) chloride to this and got a nice blue precipitate. It might not have been perfectly pure, but it was blue enough.

Disclaimer- this was also 20 years ago.




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MadHatter
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[*] posted on 29-1-2020 at 21:41
Cobalt compounds


Lion850, you hit the nail on the head about pottery
shops. Here in the states, I found a pottery shop that
carried those 2 cobalt compounds in addition to the
sulphate. Other compounds of interest include:

Chromium oxide, copper carbonate, copper oxide(black & red),
iron chromate, iron oxide(black & red), iron sulphate,
manganese carbonate, manganese dioxide, nickel carbonate,
nickel oxide(black & green), silicon carbide, tin oxide,
titanium dioxide and vanadium pentoxide.

They also sell Ohaus triple-beam scales. I never had to order
online because I lived so close(13.2 miles).

https://www.clayworkssupplies.com





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Arcaeca
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Mood: brøthér, can you spare some B̲̺̹̙̑́̓́ͧ̎ͭ̈́͜L̰̦̼̻͈͖̺͔̇̇̿ͪ̓̃̽ͦŲ̘̲̻͔̀͌͑͑̊͛̑̀͊̕E̐ͮͯ͆̔̾͘͏҉̥̫

[*] posted on 30-1-2020 at 13:20


Okay... but just buying them defeats the point of trying to make them myself for fun.
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Bezaleel
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[*] posted on 31-1-2020 at 05:37


You can get cobalt metal via e-bay. It will dissolve in HCl solution, though not quickly.

You might also wish to try cobalt(II)molybdate, which is very purple, similar to the silicate.
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