As a craft process that prints a resist paste onto the fabric before dyeing it with indigo, blueprint eludes the form of industrial production. The term ‘blueprint’ can be misleading because blueprint fabrics are not printed blue but dyed blue. The resist paste prevents the fabric from colouring in the indigo vat. After washing out the paste, a white pattern remains against the blue background.
The ingredients of the greenish resist paste, ‘Papp‘, are well-kept secrets of every blueprint practitioner. There are hardly any written records and the recipes are usually passed on from one generation to the next. But the main components of the resist paste are gum arabic and clay.
Patterns seen in blueprints are mainly regionally-inspired designs of local flora and fauna. To apply them on to the cloth, European practitioners still use handcrafted wooden blocks, either made from carved pear or linden wood, or set with brass pins or strips.
Printed fabrics must dry for at least three weeks before they can be dyed. Depending on the desired intensity of blue, the dyeing process can take up to 4 hours and requires 9 or more dips into the indigo vat. The fabrics are usually hung on small iron hooks in a star tire. The small holes along the fabric edges resulted from hanging are therefore a unique characteristic of traditional blueprint textiles.
In the temperate zones of Europe, woad (Isatis tinctoria) was the main source until Indigofera tinctoria reached the European markets. Woad has a relatively low concentration of indigo. In the first half of the 17th century, several socio-economic development factors resulted in indigenous woad having to compete strongly with imported indigo: the growing indigo production in India paired with an industrialisation-driven demand in Europe fuelled large-scale exports from India and Europe’s transatlantic colonies and contributed to a complex and horrific chronicle of slavery and exploitation. By the end of the 17th century, woad was almost completely replaced. With the synthesis of indigo by German chemist Adolf von Baeyer and the beginning of commercial production in 1897, both woad and global natural indigo cultivation collapsed. Today, most European practitioners use imported natural indigo or sometimes synthetic indigo.