Alternate Names: Synthetic Malachite, CuCO3
|If this formula is not unified correctly please contact us.|
|DENS - Density (Specific Gravity)||3.70|
|GSPT - Frit Softening Point||500C D|
|TGA - TGA||See accompanying curve image|
Conceptually, copper carbonate is CuCO3, however this form is not normally available in the market (copper carbonate basic is the article of commerce) so the powder should be viewed as a family of compounds.
This material is considered volatile during firing and thus can affect the color of other pieces in the firing. See Copper Carbonate Basic for more information.
The top samples are 10 gram GBMF test balls melted down onto porcelain tiles at cone 6 (this is a high melt fluidity glaze). These balls demonstrate melt mobility and susceptibility to bubbling but also color (notice how washed out the color is for thin layers on the bottom two tiles). Both have the same chemistry but recipe 2 has been altered to improve slurry properties. Left: Original recipe with high feldspar, low clay (poor suspending) using 1.75% copper carbonate. Right: New recipe with low feldspar, higher clay (good suspending) using 1% copper oxide. The copper oxide recipe is not bubbling any less even though copper oxide does not gas. The bubbles must be coming from the kaolin.
Cobalt carbonate (top) and copper carbonate (bottom). Left is the raw powder plastic-formed into a sample (with 2% veegum). Right: fired to 1850F. The CuCO3 is quickly densifying over the past 100 degrees and should begin to melt soon. It is long past the fuming stage.
These are pure samples (with 2% binder added) of (top left to bottom right) strontium carbonate, nepheline syenite, cobalt carbonate, manganese dioxide, bentonite (in bowl), 6 Tile kaolin, New Zealand kaolin and copper carbonate. I am firing them at 50F increments from 1500F and weighing to calculate loss on ignition for each. I want to find out at what temperature they are gassing (and potentially bubble-disrupting the glaze they are in or under). Notice how the copper is fuming and spitting black specks on the shelf, this happens right around 1500F. These stains on the shelf darkened considerably when the kiln was fired higher.
And example of how copper carbonate fumes during firing. The white sample on the left was near the copper sample, at around 1500F the fumes discolored its facing edge. These are permanent, they do not fire out but get darker with increasing temperature (this is 1950F). The kiln shelf was also discolored outward about half an inch from the copper specimen.
The top base glaze has just enough melt fluidity to produce a brilliant transparent (without colorant additions). However it does not have enough fluidity to pass the bubbles and heal over from the decomposition of this added copper carbonate! Why is lower glaze passing the bubbles? How can it melt better yet have 65% less boron? How can it not be crazing when the COE calculates to 7.7 (vs. 6.4)? First, it has 40% less Al2O3 and SiO2 (which normally stiffen the melt). Second, it has higher flux content that is more diversified (it adds two new ones: SrO, ZnO). That zinc is a key to why it is melting so well and why it starts melting later (enabling unimpeded gas escape until then). It also benefits from the mixed-oxide-effect, the diversity itself improves the melt. And the crazing? The ZnO obviously pushes the COE down disproportionately to its percentage.
The recipe also contains 2.5% tin oxide. The clear base is the best we found to host the copper blue effect (this is actually one we recalculated to source the Al2O3 more from clay and less from feldspar to get much better slurry properties). Other base recipes are more fluid, blister more easily, the slurry does not work as well and they are not as blue. There is an Insight-live.com share to see the recipe and notes at http://insight-live.com/insight/share.php?show=ruY3muruhJ1
4% copper carbonate and 6% rutile have been added to G2934 cone 6 matte base. Using a green stain should prevent this. Or some B2O3 could be substituted with SiO2 (via glaze chemistry).
These glazes are the same (G3806G), except the one on the right has 3.5% copper carbonate added. Copper is commonly thought to flux glazes, making them melt more. But in this case, the clear base is running just as much as the stained one. And I was suspicious that the micro-bubbles in the glass matrix were coming from the copper carbonate gassing during firing. But not so, as you can see the flow on the left has them also, actually it has even more.
This is the winner of a five-way cone 6 copper blue glaze comparison that started with my dissatisfaction with Panama blue. When I compared these glazes I did not just eyeball them on a tile. I compared the melt flow, thermal expansion and slurry performance of the bases (without the copper and tin). Ball-melt GBMF tests also showed bubble and color development for very thick sections. Then I tried more copper and did more flow tests. I also did leaching tests. Where needed I adjusted recipes to increase clay content (while maintaining chemistry) so the slurries would work better. Without my account at insight-live.com to keep all of this organized it would have been so much more difficult, actually, I probably would not even have bothered with the project. The final recipe, G3806C, was an adjustment to reduce the thermal expansion of this one.
Why the difference? The one on the right (Plainsman M370) is made from commodity American kaolins, ball clays, feldspars and bentonite. It looks pretty white-firing until you put it beside the Polar Ice on the left (made from NZ kaolin, VeeGum plasticizer and Nepheline Syenite as the flux). These are extremely low iron content materials. M370 contains low iron compared to a stoneware (less than 0.5%) that iron interacts with this glaze to really bring out the color (although it is a little thicker application that comes nowhere near explaining this huge difference). Many glazes do not look good on super-white porcelains for this reason.
Out Bound Links
Cupric Carbonate, Copper (II) Carbonate, Azurite
Copper (II) Oxide, Black Copper Oxide, BCO, Cupric Oxide
Cu2O, Red Copper, RCO, Copper (I) Oxide, Cuprous Oxide
Copper(II) sulfate pentahydrate, blue stone, cupric sulfate, copper sulphate
Copper(II) hydroxide, Copper Hydrate, Cupric Hydroxide
The hazards of using copper oxide and carbonate in ceramics.
The hazards of using these materials in the ceramic process
Copper carbonate decomposes at 290 °C, giving off carbon dioxide and leaving copper(II) oxide: CuCO3 (s) → CuO (s) + CO2 (g)
Copper carbonate mineral
In Bound Links
An example of how we can use INSIGHT software to determine of a glaze is likely to leach