A process for forming a three-dimensional article in sequential layers in
accordance with a digital model of the article. The process comprises the
steps of defining a layer of powder material, applying a liquid reagent
to the powder layer in a pattern corresponding to the digital model, and
repeating these steps to form successive layers. The powder comprises a
first reactive component and the liquid includes a second active
component capable of reacting with the first reactive component so that
the article is built up in layers.