Heliogravure is a technical trick using chemicals to make printing plates for intaglio engraving. The work is reproduced on metal by photographic transfer. Rops discovered that heliogravure was a practical way of transferring his drawings to copperplate. He often reworked his plates by hand, according to traditional etching techniques, sometimes arriving at a stage when a mere photochemical image was transformed into an etching which combined the photo with the original.