Test Execution Host (T.E.H.) explores the way in which geological materials are embedded in the history and functioning of technology and the way in which they are subjected to environmental change, linking computation to processes of natural material formation, transformation and decay.

T.E.H. references the life and work of computing pioneer Alan Turing. The work takes the form of a primitive, leaky computing machine, a Turing Machine (TM) which writes, computes and reads ones and zeroes on a physical tape composed of rocks and samples from local mining regions, local earth, alongside obsolete computing parts.

The Turing Machine, a conceptual conceit in the first instance, is rendered physical. It consists of a kind of playback head, which writes ones or zeroes to an endless tape across which the head can move back and forth. The Turing Machine reads data from the tape and changes state according to both data and instruction, in the process storing further data, writing to the tape. This is the essence of computation.

In order to write a one to the rock tape pre-mixed cyanotype fluid (ammonium iron (III) citrate and potassium ferricyanide - when exposed to daylight this liquid will darken to a deep blue) is dripped out, and, in order to write a zero, water is pumped from the adjacent nozzle.

Information is read back from the tape by the moving TM reader head, which registers relative amounts of light and dark. As the head moves, the Turing program or software is executed poorly due to the raw materials involved. The operation of the machine is fluid, sketchy and bound to the material constraints of light and liquid.

This cyanotype photographic process, introduced in the 19th century and used to make blueprints from technical diagrams, involves cyanide, a compound which is used in the industrial extraction of gold from low grade mineral ores. Alan Turing committed suicide through the ingestion of cyanide.