Alberta Slip black with 4% stain at cone 6

Making black using metal oxides normally involves cobalt oxide, manganese dioxide, copper oxide and iron oxide. Combined they typically comprise 10-15% of the recipe! Using the Alberta Slip GA6-B base recipe, only 4% Mason 6600 black stain is needed to get a jet black! These blacks were applied in varying thickness on a porcelain and buff stoneware before having the white second layer applied. The black glaze on the top-right tile only has 3% stain. The overglaze is a gloss white with increasing amounts of tin oxide added (4-7%). Beyond 5% there appears to be no advantage.

Related Pictures

Why would I use a heavily pigmented black glaze on a food surface?

Two mugs, black glaze on the inside, red glaze on the outside

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These are actually two different cone 6 base glazes to which I add a black stain. I trust them because I know what is in them, I formulated and perfected them myself: G2926B clear and GA6-B Alberta Slip base. They are durable, fit my clay bodies, melt well yet can host a stain without loss of gloss. I even know the chemistry, both have plenty of SiO₂ and Al₂O₃, that is a hallmark of durability. I fired these using the PLC6DS schedule. I add 5% black stain to the former and 4% to the latter, both yield a jet-black. The GA6-B requires ball milling. Stains are inherently much safer to use than raw metal oxide colorants because they are sintered as colorant/stabilizer blends. And much less is needed. Contrast that with raw metal oxides, it is common to find black recipes containing up to 15% of blends of nickel, cobalt, iron and manganese! At times the manganese alone can be 8% or more! So, I feel relatively safe using these coloured glazes on a surface that will be exposed to hot and acidic liquids.

Two black cone 6 glazes recipes. One leaches metals. Why?

Black-glazed sample tiles showing leaching

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We tested susceptibility to leaching of a stained glaze (top two) and another colored with raw metal oxides (bottom two) using the GLLE test (they were left overnight in vinegar and lemon juice). All the samples were fired using the C6DHSC firing schedule. The top two are G3914A (GA6-B Alberta Slip base with an addition of only 4% Mason 6600 black stain). There is no sign of leaching (Drano and bleach likewise did not affect it). The bottom two are G2926B transparent with 10% manganese dioxide and 5% copper oxide added (a common way to get black). The G2926B transparent base is proven, its surface shows no signs of gloss-loss in any testing we have done. But with manganese and copper added it is a very different story. Not only was this not nearly as black, but the vinegar and lemon juice matted and blued the top sections. Obviously, a ceramic stain added to the Alberta Slip GA6-B base is a far better way to make a leach-resistant black. Is it better than adding the black stain to G2926B? Yes, because far less is needed since the GA6-B base already has plenty of pigmentation.

Videos

Links

Glossary	Oil-spot glaze A mottled glaze created by double-layering glazes of different melt fluidity and color
Recipes	GA6-B - Alberta Slip Cone 6 transparent honey glaze An amber-colored glaze that produces a clean, micro-bubble-free transparent glass at cone 5-6. Works well on brown and red burning stonewares.

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