Duchek’s mocha cup #085

Name:
Duchek’s mocha cup #085JD2020m

Content and size of the cup:
150 ml, upper diameter 10 cm, height 5,5 cm

Author:
Jiří Duchek

Check out these two movies about Jiri Duchek and his work. Movie1 and Movie2

About:
A cup decorated with a mocha ware glazing technique and traditionally wood fired. Made of locally sourced clay by Jiri Duchek himself. By using this cup light cracks will come up from the glaze adding to it more patina.

[excerpt] There is a glazing technique that gives rise to complex dendritic patterns on pottery. Sometimes called Mocha diffusion, the resulting pieces are called Mochaware. The name Mocha comes from the Red sea port of Mocha, now in Yemen, a city associated in England with the export of dendritic, or moss agates (Mocha stone). The technique dates from the 1780s, and was invented in Staffordshire in the UK. The earliest written reference to it comes from the Lakin & Poole factory in Staffordshire, and mentions “mocoe beakers” in 1792-1796.

The original recipe involves a “tea” made by boiling tobacco, which is then colored with e.g. Iron oxide. The piece is first coated with a wet “slip” (very runny clay/water mixture). Then the tea mixture is touched onto the wet surface. The acidic tea reacts with the alkaline slip and the dendrites grow quickly from the point of contact.

The dendritic pattern is clearly the result of a dynamic process in which the contact line between the two liquids, tea and slip, becomes unstable. The surface tension of the tea is less than that of the slip. The instability is probably driven by a combination of capillary and Marangoni (surface tension gradient) stresses, coupled somehow to the acid/base chemical reaction. Similar looking instabilities are known in surfactant driven flows.

Refrence:

Mocha and Related Dipped Wares 1770-1939,
a book by Jonathan Rickard, The University Press of New England.