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 a first liquid , applying a second liquid to the first liquid layer in a pattern corresponding to the digital model , and repeating these steps to form successive layers . the first liquid comprises a first active component and the second liquid includes a second active component capable of reacting with the first reactive component so that the article is built up in layers .