Heliogravure

Heliogravure, or photogravure, is one of the most sophisticated photo-mechanical processes, and an intaglio printmaking process (other methods are offset, rotogravure and photo etching). Images are printed by making printing plates, then transferring the image onto paper.

A Photochemical process that creates the intaglio surface where the photographic image is etched into a copper plate.

The copper plate is used to print the image onto etching paper using inks.

It is good to use a good quality thick paper, that can draw out the ink from the recesses of the copper plate.

To conduct the classical heliogravure au grain process you have to prepare a proper positive film of the same size as the final print, containing the image that is to be transferred on a copper plate. For the purpose, use a special pigmented jelly paper (tissue paper) previously sensitized and exposed to a UV light under the positive film. After the transfer, the plate will be etched with different densities of Iron (III) chloride baths.

After that operation, every text on heliogravure says that you should first, “powder” the dry and clean plate in a dust box – the same way as in aquatint etching method – and melt the bitumen dust on a heating source, to obtain the “grained” surface – or the ground as it is called). Second, to dip the plate into a cold water tray and THEN make the coupling with the exposed pigment paper – soaked in the same container – let it stick on “the ground” and peel off the paper.

This operation, shortly described here, is very delicate because you have to convince a jelly layer swollen with water, carrying your masterpiece, to stick totally and free of tensions, to the tough and rough grained metal leaving the pliable paper where it originally stands. That is why the metal must be perfectly clean and free of  grease and dust.

In direct gravure printing, the ink is applied directly to the cylinder and from the cylinder it is transferred to the substrate. One printing unit consists of the following components:

an engraved cylinder (also known as "gravure cylinder") whose circumference can differ according to the layout of the product being made.

an ink fountain

a doctor blade assembly

an impression roller

a dryer

For indirect gravure processes, the engraved cylinder transfers ink in the desired areas to a transfer roller, and the transfer roller transfers it to the substrate.