Papa: The Gateway to Rock Glaze

While I appreciate the aesthetic contributions made by the materials we use, I'm also interested in the context and history of those materials because these offer a sense of place and time. But it isn't always easy to determine a context or reconstruct a history. Words, and their meaning(s), are often the first hurdle: There's overlap between the words used by geologists and potters, but there are also striking differences. Translation from potters terms to geologic ones enables me to research histories and place materials in context.

When I started to investigate the possibility of sourcing local geologic materials as body additions or glaze, other potters would suggest 'Papa'. This is not a geologic name of a rock type, nor is it one of the names given by geologists to a particular rock of a specific place/time (a 'formation' name). Instead, Papa appears to be a catch-all term that New Zealand potters use to refer to the fine, grey, and oftentimes crumbly, rocks that include layers of sandstone, siltstone, and mudstone. Given these characteristics, and that most potters collect this material around north Taranaki coast or somewhat inland from there, it seems that Papa most commonly refers to the Mount Messenger Formation.

The Mount Messenger Formation was deposited under an ocean during the Middle to Late Miocene (16 - 5.3 million years ago), and is part of the Whangamomona Sequence that accumulated within the King Country and Taranaki basins. Now thrust above sea level, we find the Mount Messenger Formation extending around 20 km eastward from the north Taranaki coast and offshore to the west. Based on an average geochemistry of 28 offshore samples, the Mt Messenger Formation has an 8.72 SiO2:Al2O3 ratio that places it in the stable glossy range of the Stahl Chart (geochemical data kindly provided by Mark Lawrence). I've added this material to Glazy (ID 676558; https://glazy.org/materials/676558). Local variation is expected, however, so this average composition is only a general guide.

With its desirable geochemistry and crumbly nature, Papa is a gateway for rock glaze exploration. Additions of whiting or ash as flux are a good start point. I aim to develop stable high- and mid-fire Papa glazes, and to explore the variability of this geologic ingredient. Janet Smith kindly provided her high-fire Papa glaze recipe, and adding titanium dioxide to this base generated interesting results (see photos). More experimentation is planned.