In an image-forming medium, a sheet of paper is coated with a layer of microcapsules which is composed of a binder material and a plurality of microcapsules filled with dye and uniformly distributed in the binder material. A second conveying path branches from the first conveying path. The polymer matrix keeps oppositely charged pigment particle from agglomerating. Etching is conducted within the opening through the nitride-comprising shield. The portion of the duct leading to the mouth is sealed off, while the portion leading to the salivary gland is temporarily left open.