Copper Sulphate - what' it good for?

[Chantay Poulsen]

Hi all,

I was working on my shopping list for the local ceramics supplies store and saw Copper Sulphate listed under coloring oxides.  It is a brilliant teal blue.  I have never seen this in a reciepe.  Has anyone else?  What did the resulting glaze look like?

[Norm Stuart]

If you are looking at novel materials, do this Google search for decomposition temperature or melting temperature.

http://www.google.com/#q=Copper+Sulphate+decomposition+temperature

or

http://www.google.com/#q=copper+sulfate+wiki

to get this page

http://en.wikipedia.org/wiki/Copper%28II%29_sulfate

This Wikipedia page (below) shows the blue hydrated version loses its water at 230 F to become the teal Anhydrous Copper Sulphate which then decomposes into Black Copper Oxide and Sulphur Trioxide gas at only 752 F (560 C), or Sulphur Dioxide depending on the conditions.

So you can see, working in ceramics, you're not going to have Copper Sulphate, but only Black Copper Oxide CuO.

So you might get lucky with this Google search 

http://www.google.com/#q=Digitalfire+copper+sulphate

http://www.google.com/#q=Digitalfire+black+copper+oxide

Which takes you to these pages

http://digitalfire.com/4sight/material/copper_sulfate_239.html

http://digitalfire.com/4sight/material/copper_oxide_black_237.html

Here's both pages side-by-side. (click on the photo to expand it to full size)

Digitalfire quickly tells you Copper Sulphate has only 31.85% as much Copper Oxide as Black Copper Oxide. The balance of the Teal Blue material burns-off in the kiln as sulphur trioxide gas listed as LOI = Loss on Ignition.

So the resulting glaze color will be exactly the same as if you had added 31.85% as much Black Copper Oxide — or 49.46% Copper Carbonate which comes from the Digitalfire page for Copper Carbonate.

You won't always find a decomposition temperature for every material, but instead will find the Melting Temperature and the Boiling temperature - and that's good news if the temperature listed is hotter than your kiln — it means it's a suitable glaze material.

Take the ceramic flux Lithium Fluoride as an example which melts at 1,553 F (about ^013) and boils at 3,049 F, well above Cone 11 which is only 2,294 F.

If you could get a kiln that hot, the Lithium Fluoride will quickly melt then boil — then condense back into liquid Lithium Fluoride as soon as it finds a place cooler than 3,049 F and crystallizes into a solid at 1,553 F.

http://en.wikipedia.org/wiki/Lithium_fluoride

Some potters are convinced Lithium Fluoride breaks down into Lithium and dangerous Fluorine gas, but the heat required for that is phenomenal, far, far hotter than the 3,049 F which makes it boil. A temperature so hot the number isn't even listed — and no one has a kiln that hot unless you have a research lab.

[Jeff Poulter]

I have used Copper Sulphate in recipes for electric fired self-reduced reds.  The sulphate dissolves better in water and gives you a better looking red when using a really fine mesh of Silicon carbide.  Like Norm's numbers indicate, it is not even as strong as the carbonate, but you don't need a whole lot when working with self-reducing copper reds.  jhp

[Chantay Poulsen]

Thanks for the info guys.

[Marina Reijsmeijer (Kleierij)]

I used copper sulfate in pit fires. Pour a solution of copper sulfate in water (1tbsp/2 cups) over your bisque ware before putting it in the pit and/or sprinkle copper sulfate powder over the wood in the pit. Results:  reddish spots.

Spraying copper sulfate solution on bisque under a clear glaze and fire cone 6ox gives a watery blue effect.