“Portraits were printed in woodburytype, a fully continuous tone photomechanical process using carbon black, superbly stable from light fading. This process required negative lead matrices, filled with hot, gelatin-based, pigmented ink. A goodquality india ink was used to produce black images. Woodburytype images were also printed in dark-brown, brown, or purple-brown colors resembling gold-toned albumen photographs in which black was mixed with red pigments” (cf. Stulik& Kaplan, Woodburytype, CCI).
The lead mold, the negative matrix needed a positive matrix: a gelatin relief matrix like those. A high-power hydraulic press was used to press the gelatin matrix into some smooth, perfectly leveled plate of lead, forming then one, two, three negative lead matrices (molds). After a solution of gelatin, albumen, sugar, and ammonium dichromate was dried, it was exposed to sunlight under a glass negative of Nadar or Carjat.