The red dye then colors the newly exposed white sections red, and over-dyes the unseal indigo with red to produce a midnight-blue. Opening one set of the remaining bindings reveals sections that have received neither dye and remain white; opening the other set re-exposes the pure indgo work.
The red dye is from the root-bark of the Morinda citifolia tree. The root bark, having been pounded to a pulp, is hand-squeezed into water to release the dye. Alum is added in the form of powered leaves or bark from Symplocos sp trees to complete the mordant process. The cotton is left in the dye bath for a full day, then dried before re-dyeing. Careful manipulation of the mordant chemistry rnsurews the desired shade of red is produced.