[DMCosta]

Hi,

I am new to making my own glazes and I have a low fire recipe that calls for "Copper Oxide" It is a bright turquoise blue green glaze from a book published in England. When they say "copper oxide" do you think they mean "Red Iron Oxide" or my "Copper Oxide Black"? Thank you!

~Dianna

[neilestrick]

Not red iron oxide. Yes, black copper oxide. Copper is also often used in the carbonate form.

[Mark C.]

DMCosta, on 11 July 2012 - 01:02 PM, said:

Hi,

I am new to making my own glazes and I have a low fire recipe that calls for "Copper Oxide" It is a bright turquoise blue green glaze from a book published in England. When they say "copper oxide" do you think they mean "Red Iron Oxide" or my "Copper Oxide Black"? Thank you!

~Dianna

For my High fire (cone 10) greens I use copper carbonate a fair amount
A little black copper but only in oribe glaze.
My guess is use copper carbonate
This is where a few small tests would answer all this real fast.
Mark

[TJR]

DMCosta;
When they say copper oxide, they mean copper oxide. Red Iron Oxide will give you a completely different colour depending on the percentage used.I use copper carbonate and black copper oxide. It's worth making some tests, and reading up on the use of oxides in glazes. Any beginning ceramic text worth it's salt should help you out. There is always the internet.
TJR.

[DMCosta]

Thank you everyone for your suggestions and help. The reason why I was asking is because I did make the glaze originally with the black copper oxide and after viewing the fired test tile it looks totally off from what it should. So I wasn't sure if I added the correct oxide. I will continue to look into it further and experiment, thanks again.

~Dianna

[Marcia Selsor]

What did it look like and what was it suppose to look like?I recently taught in a university and found a recipe transcribed with the wrong copper. it should have read copper carbonate. the student who followed the recipe from the glaze binder in the glaze room was very disappointed. i was familiar with the recipe and saw the error. tell us what you were expecting and what you got.
MArcia

[Marcia Selsor]

This is a tip from my old friend, Tom Buck, a chemical engineer and ceramic artist. If you are using red copper oxide and have trouble with it floating to the top, add a dash of dish detergent to the glaze. It will help the copper mix in.
Marcia

[Iforgot]

A quick tip, don't use copper oxide, use copper carbonate, and whatever the recipie calls for of copper oxide replace it with half of that of copper carb and half salt. Good luck!

[neilestrick]

Iforgot, on 17 July 2012 - 09:53 PM, said:

A quick tip, don't use copper oxide, use copper carbonate, and whatever the recipie calls for of copper oxide replace it with half of that of copper carb and half salt. Good luck!

Please explain. How does half as much copper carb plus some water soluble salt equal copper oxide?

[JBaymore]

Note also that black copper oxide is typically provided in a coarser particle size than copper carbonate. So it tends to produce a slightly more mottled coloration.

If you substitute oxide for carbonate or carbonate for oxide you have to account for the weight difference in the chemistry of the two materials supplying the actual coloring copper oxide in the final melt.

Most copper glazes are sensitive to the firing process. For example, if the glase is a copper red based color development...... you need the appropriate amount of reduction at the exact correct time. If a firing is extended at very high tempoeratures copper is volatile from the glaze and some of the content is going off in the kiln gases.

best,

............................john

[Marcia Selsor]

neilestrick, on 18 July 2012 - 08:00 AM, said:

Iforgot, on 17 July 2012 - 09:53 PM, said:

A quick tip, don't use copper oxide, use copper carbonate, and whatever the recipie calls for of copper oxide replace it with half of that of copper carb and half salt. Good luck!

Please explain. How does half as much copper carb plus some water soluble salt equal copper oxide?

I'd like to know that too. I always thought you needed about 1.5 x as much copper carb as 1. of copper oxide...and no knowledge of salt.
Marcia

[Michael S.]

Marcia Selsor, on 12 July 2012 - 09:00 AM, said:

This is a tip from my old friend, Tom Buck, a chemical engineer and ceramic artist. If you are using red copper oxide and have trouble with it floating to the top, add a dash of dish detergent to the glaze. It will help the copper mix in.
Marcia

I've found that if you add a small quantity of CMC gum solution to your glaze it will help keep the copper oxide in suspension. More so with the black copper oxide than the red.