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Field CollectingUK - Finding and collecting copper

9th Aug 2018 19:33 UTCPaul Wheeler

Hello

I'm currently undertaking a pottery apprenticeship of sorts in Stoke on Trent and I'm really interested in using material that I've sourced myself in my work.

I have access to decent clay for the bodies of my pieces, but I am looking for sources of copper which can be incorporated into my glazes to add colour (green in an electric kiln firing and red in a gas reduction firing).

Does anyone know where I would be likely to find small quantities of copper ore in the UK? Even fine dust would useful to me. I have found a few mines that are now closed or have been turned into museums but its unlikely they would let me carry off a load of their rocks.

Any help you could give me would be massively appreciated.

Thanks

Paul

9th Aug 2018 20:32 UTCTom Goodland

Hi Paul,

do you know what type of copper ore, whether a sulphide or carbonate (like malachite)? I know little about pottery glazing, but would have thought they would be very different to work with.

cheers

tom

9th Aug 2018 20:46 UTCAlfredo Petrov Manager

I'd imagine it would be best to use the metal oxide (like cuprite) for coloring glazes? Other secondary minerals, like carbonates (malachite, etc) or hydrous species would release gases (CO2, H2O) on firing and make the glaze frothy, or does the gas dissipate sufficiently rapidly to not affect the glaze?

9th Aug 2018 22:07 UTCAndy Lawton

The Alderley Edge mines up the road in Cheshire could be a relatively close source of malachite for you, although getting permission to collect may well be unlikely. Small amounts of cobalt oxides were also mined there in the past for use in blue glazes. It might be worth you asking the Potteries Museum & the Wedgwood museum if they have any old documentation about this subject (Wedgwood was something of an innovator in this field)

9th Aug 2018 22:20 UTCPavel Kartashov Manager

Cuprite will oxidize up to tenorite. Are you need in a black glaze?

May be oxychlorides (atacamite type) will be better?

10th Aug 2018 01:19 UTCHiro Inukai

Both copper oxide and copper carbonate are used in powdered form as glaze ingredients, although it is the latter that is far more common. Copper oxide as a glaze colorant tends to be extremely potent, and if I recall correctly, it needs to be milled extremely finely and does not mix easily in suspension. Copper carbonate is added into glazes at proportions typically ranging from 0.25% to as much as 5% although at the high end of the range, leaching is a concern.

In reduction firing, copper reds form at levels ranging up to 0.5%. Greens form in oxidation or reduction between 1% to 4% if memory serves. The presence of other elements, such as calcium, barium, lithium, and strontium can also affect color, resulting in blue, teal, and red with corresponding changes in the surface quality.

Most glaze materials have some contamination with organic substances, and these are lost on ignition. But the primary source of organic compounds actually comes from the clay body itself, and these have to be burned off well before the glaze begins to vitrify or else bloating will occur. Colorant oxides are typically only present in small quantities.

11th Aug 2018 11:04 UTCPaul Wheeler

Thank you for your replies.

It would be the oxide and carbonate forms that I would be interested in, though I am happy to test any material.

I wonder how feasible it is to stumble across a chunk of malachite in a stream or on the beach? Surely it must exist above ground for those early miners to have know they needed to dig it up? Or is it really rare?

I've enquired about joining a mining and caving club that goes to Alderly Edge, but I'd love to find some myself if possible.

Thanks

Paul

11th Aug 2018 12:33 UTCKeith Compton 🌟 Manager

The Royal Society of Chemistry has a few articles on copper glazes.

One of relevant interest is below:

http://www.rsc.org/learn-chemistry/content/filerepository/CMP/00/006/301/B006_Story_of_Egyptian_blue%202.pdf

11th Aug 2018 16:35 UTCPaul Wheeler

That's really interesting, thank you Keith. I've actually had a go at making Egyptian faience in the past.

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