A photomechanical printing process based on patents taken out by William Henry Fox Talbot in the 1850s. The process was improved by Karel Klič in 1878 and only then developed commercially. In Klič’s process a copper plate was coated with a fine bitumen dust to provide grain and then heated to cause it to adhere. A carbon print was transferred on to the plate and developed in warm water to give a negative relief image. Etching solutions of ferric chloride were applied successively so that the plate was etched to different depths. The plate was then inked and the image transferred to paper in a press. There were many improvements to the process from the 1880s, but the essentials remained the same. Around 1900 photogravure was used to reproduce the work of some of the most distinguished photographers of the age. The process has always been favoured where high-quality reproductions at a reasonable cost are required. ‘Heliogravure’ is applied to a type of photogravure developed in France in the 1850s from the ‘heliography’ of nicéphore Niépce, which used bitumen made light-sensitive as a resist in etching the plate, and it is also an alternative name for photogravure widely used in Europe.