Mocha Diffusion Explained
The past few weeks a video of ceramic artist Kevin Kowalski has gone viral on social media. Kevin is the creator of mesmerizing pottery designs using a pottery painting technique called mocha diffusion. This technique is a chemical reaction between wet clay and a specially prepared acid liquid that creates stunning tree and feather-like patterns.
What is Mocha Diffusion ?
Mocha Diffusion is a pottery painting technique that involves a chemical reaction between an acid and a base liquid. It sounds like a yummy coffee drink, but mocha diffusion is a surface decoration developed and used in the southwest of England, now made famous by Kevin’s viral videos. Through a reaction between acid and alkali, intricate veined patterns reminiscent of trees or ferns are created in this process. The resulting designs are intricately beautiful.
In this technique, thick slip is applied to wet or leather-hard clay that hasn’t started to change color in drying. Then an acid/color mixture is applied. The leather-hard pot is dipped, brushed or poured with slip. While the surface is still wet, and before it has begun to lose its shine, the acid/color mix is dripped or trailed into it. Using a well-loaded brush held just touching the slip. If the viscosity of the slip, and the acid/color mix is right then the feathering pattern will take place quite naturally, as the acid eats a fern-like pathway through the slip pulling the colorant with it. The surface tension of the acid is less than that of the slip.
Mocha diffusion was traditionally done on both red and white earthenware, but may be done on almost any clay body at almost any temperature. A Smooth clay body with a high degree of ball clay or plastic kaolin is the most preferred.
It is ideal to use the technique on high-fired ware that does not need to be glazed. Conventionally, the surface is coated with a thin coat of clear glaze, or transparent colored glaze, but this might cause the color to bleed out or become absorbed into the glaze, particularly at temperatures above Cone 4.