Hervé Sachy has been working with Copper photogravure etchings for over 40 years, but was, due to the ban of dichromate forced to find a new way to do etchings. This resulted in a chrome free copper photogravure process – better for both the artist and the environment.
Hervé Sachy, who has lived in the South of France for the last 40 years, learned traditional etching techniques as a student in Paris. During all those years of etching, Hervé’s developed a passion for working with metal and specifically copper. Hervé also soon found the symbiosis between etching and photography. After various attempts, he finally realized that photography had started with gravure printing.
As an autodidact, Hervé Sachy learned the copper photogravure technique of the 19th century, and after a few years of works, he managed to master the technique.
In 2017 it became virtually impossible to find dichromate – the essential chemical compound the copper photogravure process – in Europe.
“This ban is in my opinion completely legitimate when we know the toxicity of these chromates for human and animal health and also for our planet.”
4,4′ – Diazidostilbene-2,2′ – disulfonic Acid Disodium Salt Tetrahydrate C14H8N6Na2O6S2·4H2O
The ban of dichromate in Europe was the motivation for Hervé to search for a new copperplate photogravure process, one that is more ecological and less toxic. Hervé Sachy receives artists in his studio and believes it is important to teach students how to work with legal and environmentally friendly products.
The new chrome free copper photogravure process
1. Gelatin paper sensitization as in the classic copper photogravure process
As in the classical process, we must sensitize a gelatined paper or carbon tissue with an aqueous solution of this product DAS (diazidostilbene), here at 3%. It is not easily soluble in water.
2. Positive film exposure
After drying the DAS-sensitized gelatin paper, a digital positive film and the sensitized paper are exposed to UV rays for a very precise time of a few minutes (specific to each exposure system): the exposed parts (the light areas of the film) will become insoluble in hot water as opposed to the dark areas which will dissolve in hot water during the following development.
3. Hydration & adhesion on the copperplate
After exposure, the paper is rehydrated in a mixture (water+alcohol) at low temperature and plated on a clean degreased copperplate and the adhesion is maintained for about 15 minutes.
4. Developing the plate
The development consists of melting in hot water (about 50°C) the insolated parts which have received the least light, the dark areas. The bright parts of the image have received more UV and do not melt or little with the warm water: they will give the bright areas of the image. This operation will take a few minutes, depending on the tonality of the image.
5.Drying & stabilization of the plate (copper + gelatin layer)
I usually let this stabilize overnight before proceeding to the final engraving, but it can also be done after 5 or 6 hours spent in front of a fan. Here are some photographs of these gelatinized plates ready to be engraved with iron perchloride baths or to receive an aquatint if it has not been done on the plate before the process.
6. Aquatinting or aquatint on copperplate
The realization of aquatint is necessary in photogravure to create a pattern engraved in copper which will later, at the time of printing on paper, will retain the printing ink. This pattern can be realized at two distinct moments of the process: either at the beginning on the naked copperplate or at the end using the gelatin developed on the copperplate. The 2 methods work well and they also each have their advantages and disadvantages. In addition, one can choose either rosin or bitumen. A grain box is needed to apply a bitumen or rosin powder either on the copper at the beginning or on the gelatine layer at the end. In both cases, the powder must be fixed by heating it until it melts.
7. The etching using iron chloride
Here is a typical installation to practice the final etching: several trays to receive the different iron chloride baths at various concentrations and the last bath to remove the gelatin at the end with hot water. First, the blacks of the image are etched, then the dark grays, then the medium grays to finish with the last lightest grays. This is an operation that lasts between 20 and 30 minutes on average. With the DAS, the action of light on the gelatin is less powerful and we will notice it quickly. With this product, the etching phase is faster.
The engraving starts faster than with dichromates, almost immediately and it takes a bit of practice for the first times.
A few steps of an DAS etching based on an old gravure by Goya:
8. Printing on paper
It is obviously necessary to have access to an intaglio press or better to own one, here is the one in Hervé Sachy’s studio:
Many papers are suitable for photogravure, the main thing is to know them well and to plan a preliminary soaking so that it goes to seek the ink at the bottom of the engraved plate.
I use traditional oily inks in intaglio printing, the same as those used in conventional printmaking.
Some prints of plates etched with this new DAS process:
Thank you for your comment, indeed there are not many gravure printers and especially in Europe. One thing is certain, chromium 6 is very dangerous to health, it is a cumulative poison, and on the other hand I live in Europe and so here since 2017, it is impossible to find a supplier of dichromate, which makes it essential to do otherwise if we want to continue this technique of rotogravure on copper. We no longer have a choice here . So, if we can’t use chromium, there will soon be no more gravure printers in Europe at all. If I lived on another continent, I would certainly have continued with dichromates.
I also know about the reduction of Chromium 6 salts to the less toxic Chromium 3, but I am no longer interested in this issue because, I repeat, sorry, we no longer have access to this Chromium salt in this part of the world where I live and work.
The title of my article is Chrome Free Gravure. DAS is also a chemical, which can also explode if you don’t know how to handle it, more new and maybe one day, it will also be recognized as dangerous for health. I am also a trained chemist. I did not say that DAS is not dangerous, but one thing I am sure of is that it does not contain heavy metals, which accumulate in nature and in the food chain if we throw our residues down the drain or in nature. In my workshop, it is always kept cool and used with protective gloves and protection
[….]“This ban is in my opinion completely legitimate when we know the toxicity of these chromates for human and animal health and also for our planet.”[…]
Sorry I do not agree on that….
a) There are industrial applications even for photo-hardening resists, which are authorized from the ECHA, which use dichromates
b) The ban on dichromates applies only in the EU and not worldwide….
c) The amount of dichromate used for that kind (Art, Printing, Etching) of work is negligible. Additionally there are not so much people which are using dichromate in that manner.
d) Mainargument: With Vitamin C as reducing agent* there is a good possibility for reducing the toxicity of Cr(VI) compounds, because Cr(III) is a natural form of the element chromium see https://www.photrio.com/forum/threads/dichromate-waste-treatment.135482/
e) and with DAS: If you look at the MSDS of this substance you will find following phrases “The toxicological properties of this substance have not been fully investigated.” or “No data available”
Sources: E.g. >Safety Data Sheet: CDX D0022msds 67032<) which means there can be hidden pitfalls with that chemical, too.
Or directly said with the citation above in mind: "We do not know by now the toxicity of these diazo-compounds for human and animal health and also for our planet"…..
Furthermore from my chemical background…..DAS has two azido groups and I know (very good, own experience) that inorganic azides of lead, copper and silver are very sensitive and detonate even they are phlegmatized with water. So I think it´s a very good idea to keep waste with DAS away from waste/salts with copper or silver. The other point is that hydrazoic acid has the same toxicyty like prussic acid. There could be the possibility that strong mineral acids relase hydrazoic acid out of DAS. So avoid mixing DAS containing waste with acid waste….
Disclaimer: I find it good to look for other ways to do it….but do not get a false sense of security….
bj68