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Ceramic Review is the magazine for contemporary and historical ceramics, ceramic art and pottery.


Ceramic Review Issue 305

September/October 2020

Roelof Uys, lead potter at the Leach Pottery in St Ives, shares the recipe for the iconic Tenmoku glaze they use on their Standard Ware range in the Leach Studio.

Leach Standard Ware | Photograph by Sarah White

The iron-rich stoneware glaze known as Tenmoku has been used by studio potters in the West for many decades and was likely first introduced by Shōji Hamada when he and Bernard Leach began working together in the early 20th century. Although it remains one of the most iconic glazes and a staple of makers who work in the Leach tradition, it has often been viewed as old fashioned and synonymous with the standard dismissal of ‘brown pots’ levelled by its detractors. Although I agree with some criticisms, I feel that these opinions are often rooted in a lack of understanding about the subtleties and beauty of this glaze, coupled with a glut of bad examples.

The Tenmoku that we use in the Leach Studio was given to us by Warren MacKenzie during his residency in 2013. I had started my role at the Leach just a few months earlier and was beginning work on a Standard Ware range through which I wanted to reflect our heritage, but with a contemporary feel. I also wanted the range to be a good vehicle for training our apprentices in the various skills necessary to become skilled studio potters.

One of the first things I learned about Tenmoku is the importance of application. All our pots are dipped in large buckets of glaze with great care given to even application; the thickness of the glaze is crucial, and we use a hydrometer to determine the correct ratio of glaze material to water. I sometimes dip or wet part of a piece before glazing, which will cause that area to absorb less water and leave a thinner covering of glaze that can be used to create a more varied overall aesthetic. One of my favourite qualities of this glaze is the way it breaks from deep black to a beautiful rust colour over textured surfaces and sharp angles.     

RECIPE

Potash Feldspar    48%

Flint or Quartz*    24%

Whiting    17%

China Clay    11%

+

Red iron oxide   09%

(adding only 1-2% iron will produce
a celadon glaze)

Work by Roelof Uys | Photograph by Sarah White

Leach Standard Ware Mug | Photograph by Sarah White

*Recently we discovered that the milling process for flint in the UK has changed, which caused our glazes containing it to settle very quickly after stirring. This problem was remedied by replacing Flint with Quartz in all our recipes.

TECHNICAL NOTES: 

The clay body we use is DSS from Doble’s with 0.25% added iron oxide.

We use about 6-7 litres of water per 10kg of glaze material and the mixture is strained through an 80-mesh sieve. 

The hydrometer reading is 55 on a Baume 15°C scale.  

We fire the pots in a reducing atmosphere to cone 9 or 10 (Orton) over 11 to 13 hours. 

 

The Leach Standard Ware range and work by Roelof Uys is available from leachpottery.com

Subscribe to read this article in the September/October 2020 issue of Ceramic Review