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When you've been a potter long enough, you realize that things just... go away. Sometimes, it's a manufacturer's fault--I still haven't forgiven Mason for discontinuing their chrome-free black stain. Sometimes, though, they simply disappear. Ceramic materials are sometimes manufactured, like my favorite black stain, but more often, they're dug up from the ground. And natural resources can be limited, for whatever reason.
I remember the first time I saw this happen, when I was still an undergrad. Albany Slip was a naturally occurring clay mineral, very high in iron and fluxes. At stoneware temperatures, it's a natural glaze; if you've ever seen a vintage stoneware beanpot with a chocolate brown, semi-gloss glaze, you've seen Albany Slip. It was also commonly used as an ingredient in other glazes, like a temmoku I had, contributing iron and flux to the mix. When the company producing it announced they'd stop selling it, it wasn't because the mine ran out. There was plenty left, it just happened to be underneath the city of Albany, New York. The state capital. I suppose, if you were a potter living there you could dig it out of your backyard. The rest of us settled for the less useful Alberta Slip, or scrounged old bags of Albany from the stocks of retiring potters, hoarding them like Gollum hissing Precioussss.
In 2000, it happened again. Gerstley Borate was a calcium/borax/silica mineral, nearly a glaze on earthenware or raku. It was also a popular component of mid-range stoneware glazes, where the borax acted as both a flux, lowering the melting temperature, and a glass-former (boro-silicate glass, anyone?). Everyone used Gerstley Borate; I even had 10% in my Best Possible White. Suddenly, Hammill & Gillespie announced they'd no longer be mining it, due to safety issues at the mine. There was about a six-month supply left.
That six-month supply lasted about a week--panic buying cleared the shelves. Companies rushed synthetic substitutes to market: Boraq, CadyCal, Laguna Borate. None worked exactly the same, all were more expensive. Then Laguna Clay Company announced that they'd found an entire warehouse full of unprocessed Gerstley Borate, and it was available again. The supply lasted years, though I think it's finally run out. I reformulated BP White using a synthetic, Ferro Frit 3195, and now only use Gerstley by the teaspoon in my overglazes. And still have a 50 lb. bag in the shed I'll probably never finish.
To a geologist, there are many kinds of feldspar: orthoclase, oligoclase, anorthite, albite. To a potter, they all simplify down to two: soda and potash. Feldspar is the backbone of a stoneware glaze. It provides silica for glass, alumina for strength and stiffness, and sodium or potassium to make the whole mix melt. Tweaking the mix with other fluxes, a little clay or silica, metal oxides for color, gives us nearly the entire range of ceramic glazes.
For years, the go to soda spar was Kona F4. I never used it much--my sodium glazes were based on Nepheline Syenite--so I didn't really notice when it disappeared, just that ceramics Google was looking for substitutions. Checking now, it looks like it's been gone for twelve years, victim of a mine fire and closure, and MinSpar 200 has taken it's place.
There used to be a lot of varieties of potash feldspar. If you look at old recipes scribbled on the backs of envelopes, you see Kingman Spar, Oxford, Buckingham. In recent years, they've all devolved to Custer Feldspar, in the iconic blue bag, Impact font on a hexagonal label. It was easily the most recognizable bag in the materials room, and we'd go through a bunch of it.
In January, word came down that Custer was no longer available; the mine producing it was bankrupt. The last few pounds at Georgies were being sold in 10 lb. lots at premium prices. I don't use a lot of Custer, but it does form the basis of many of the colored glazes I put on banks and incense dragons. I mixed up a batch of Shaner Orange yesterday to glaze stegosaur banks, substituting out G200 Feldspar instead. We'll see how they look after the firing.
I remember the first time I saw this happen, when I was still an undergrad. Albany Slip was a naturally occurring clay mineral, very high in iron and fluxes. At stoneware temperatures, it's a natural glaze; if you've ever seen a vintage stoneware beanpot with a chocolate brown, semi-gloss glaze, you've seen Albany Slip. It was also commonly used as an ingredient in other glazes, like a temmoku I had, contributing iron and flux to the mix. When the company producing it announced they'd stop selling it, it wasn't because the mine ran out. There was plenty left, it just happened to be underneath the city of Albany, New York. The state capital. I suppose, if you were a potter living there you could dig it out of your backyard. The rest of us settled for the less useful Alberta Slip, or scrounged old bags of Albany from the stocks of retiring potters, hoarding them like Gollum hissing Precioussss.
In 2000, it happened again. Gerstley Borate was a calcium/borax/silica mineral, nearly a glaze on earthenware or raku. It was also a popular component of mid-range stoneware glazes, where the borax acted as both a flux, lowering the melting temperature, and a glass-former (boro-silicate glass, anyone?). Everyone used Gerstley Borate; I even had 10% in my Best Possible White. Suddenly, Hammill & Gillespie announced they'd no longer be mining it, due to safety issues at the mine. There was about a six-month supply left.
That six-month supply lasted about a week--panic buying cleared the shelves. Companies rushed synthetic substitutes to market: Boraq, CadyCal, Laguna Borate. None worked exactly the same, all were more expensive. Then Laguna Clay Company announced that they'd found an entire warehouse full of unprocessed Gerstley Borate, and it was available again. The supply lasted years, though I think it's finally run out. I reformulated BP White using a synthetic, Ferro Frit 3195, and now only use Gerstley by the teaspoon in my overglazes. And still have a 50 lb. bag in the shed I'll probably never finish.
To a geologist, there are many kinds of feldspar: orthoclase, oligoclase, anorthite, albite. To a potter, they all simplify down to two: soda and potash. Feldspar is the backbone of a stoneware glaze. It provides silica for glass, alumina for strength and stiffness, and sodium or potassium to make the whole mix melt. Tweaking the mix with other fluxes, a little clay or silica, metal oxides for color, gives us nearly the entire range of ceramic glazes.
For years, the go to soda spar was Kona F4. I never used it much--my sodium glazes were based on Nepheline Syenite--so I didn't really notice when it disappeared, just that ceramics Google was looking for substitutions. Checking now, it looks like it's been gone for twelve years, victim of a mine fire and closure, and MinSpar 200 has taken it's place.
There used to be a lot of varieties of potash feldspar. If you look at old recipes scribbled on the backs of envelopes, you see Kingman Spar, Oxford, Buckingham. In recent years, they've all devolved to Custer Feldspar, in the iconic blue bag, Impact font on a hexagonal label. It was easily the most recognizable bag in the materials room, and we'd go through a bunch of it.
In January, word came down that Custer was no longer available; the mine producing it was bankrupt. The last few pounds at Georgies were being sold in 10 lb. lots at premium prices. I don't use a lot of Custer, but it does form the basis of many of the colored glazes I put on banks and incense dragons. I mixed up a batch of Shaner Orange yesterday to glaze stegosaur banks, substituting out G200 Feldspar instead. We'll see how they look after the firing.
