Jump to content

Sycamore Pottery Is Selling Red Copper Oxide, Anyone Have Info


oldlady

Recommended Posts

i have never heard of this and wondered whether it is a good thing to have.  digitalfire says something a chemist could understand but i cannot.  is it worth buying if i only want to use it in my green ^6 glaze which is done with copper carbonate?  only reason i care is that it is close and cheap.

Link to comment
Share on other sites

'Red copper is a reduced form of the normal black copper oxide (CuO). In normal oxidizing firings it will transform to the cupric oxide form (CuO) to produce the normal green coloration in glazes and glass. If fired in reduction, it will maintain its Cu2O structure to produce the typical copper red color. See CuO, Cu2O oxides for more information.'

 

http://digitalfire.com/4sight/material/copper_oxide_red_238.html

Link to comment
Share on other sites

It could be worth having, but you'll need to re-figure out your quantities.  Here's a little math to explain.

 

Copper carbonate, which is really Cu2(OH)2CO3 has a molar mass of 221.116 g/mol, which decomposes into two black copper (II) oxides (CuO) with a molar mass of 79.545 g/mol.  Cu2O (red copper(I) oxide) has a molar mass of 143.09 g/mol.

 

This probably sounds meaningless, but what it means is that when you've got the same number of molecules of all three of these compounds,  Copper carbonate is going to be heavier, then Copper(I) oxide, then copper (II) oxide.  

 

One basic copper carbonate molecule decomposes into two copper (II) oxides when heated in an oxidizing environment.  That is to say, it loses 62.026 g/mol of hydrogen, oxygen and carbon, leaving two molecules of CuO weighing 79.545 g/mol.  But remember, you now have twice as many copper oxide molecules than carbonates.  This is how your normal glaze works when fired.  So if you usually add 221.116 g of Copper carbonate to a glaze, you'd need to add 159.09 grams of Copper (II) oxide--black copper oxide. Knowing this doesn't really matter, but it illustrates how to do some math to help you in doing further chemical figuring.  Looking up the molar masses of compounds you might use will help you figure out proportions in relation to compounds you already use.

 

​The important part:  Red copper oxide and basic copper carbonate have the same number of coppers in them per molecule.  So that means a ratio of 143.09 g/mol to 221.116 g/mol. That gives you a long, ugly number:  0.64712639519528.  That, however, is the number by which you need to multiply the weight of your copper carbonate to get the weight you need of red copper oxide.    Let's pare that back to 0.647 just to make it easy.  So if you add 100 g of copper carbonate, you need 64.7 g of red copper oxide.  Not a hard and fast number, though, just a place to start your testing.

 

I hope this helps.

 

And if anyone see an error in my math or reasoning, please feel free to correct me.

Link to comment
Share on other sites

OMG!               thanks.................................never mind.................................. :(

 

Fear not OldLady.  I think what they're saying is:   you need less of the red stuff than the black stuff, so if they are the same price, the red stuff works out cheaper.

 

On the other hand if the red stuff is dearer than the black stuff, the price difference is either the same or worse.

 

Compare the price of the two, and only buy the red if it's going to work out cheaper.

 

 

At least, that's what I make of the above comments..................

Link to comment
Share on other sites

Oldlady,

 

please forgive me.  I certainly didn't intend to scare you off using red copper oxide.  My intent was to empower you to be able to figure out similar things in the future.  It can be very helpful information. If one of the cobalts we commonly use is on sale and you use the other, you can figure out how to modify your recipe.  Or any colorants, really.  The molar mass of any compound we use is easily found through google or wikipedia.

 

If you're not interested in that or you find it overwhelming, you only need to know that you use 65% of your original copper carbonate amounts in any glaze you want to make it work.

 

Again, I apologize.  

Link to comment
Share on other sites

tyler, HOW COULD I FORGET TO SAY "THANK YOU" ADDED 1-29-2015

 i may not use the info you so generously gave but someone here will find it helpful.  i could not see when i was in grade school and did not understand why math was so hard.  got glasses at 13 and was surprised that i could see bricks in buildings across the street.  i understand basic math now because i have translated everything i can into dollars and cents. (not sense!)  part of the problem was that we were taught to count from one to ten and that meant everything after that was off by one.

 

think about it, 1to 10 is ten  10 to 20 is more than ten   20 to 30 is more than 10  how can you subtract 7 from 23 and not get messed up?

Link to comment
Share on other sites

I have one raku glaze recipe that calls for red copper oxide - I think it came from Val Poulton's book.  As i recall it was weird to mix which is consistent with the coating on it.  The glaze didn't look like the picture in the book but seems like raku seldom does.  But if it was cheap i would get some and try it more in raku.   rakuku

Link to comment
Share on other sites

Archived

This topic is now archived and is closed to further replies.

×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.