Ferric Ammonium Citrate Photogravure

	Ferric Ammonium Citrate Sensitized Photogravure

Ferric Ammonium Citrate Sensitized Photogravure
Sep 17, 2023

Many thanks to the Carbon Printers who have been experimenting with this sensitizer, particularly Halvor Bjoerngaard who wrote The Chiba System, A Non Toxic Alternative to the Dichromate Processes and the recommendations of Habib Saidane who is experimenting with FAC and carbon.

I tried this sensitizing process many years ago and it failed miserably. I do not remember what went wrong exactly. This was probably around the same time I was experimenting with DAS which was 2013. I have never felt like DAS was a viable and completely safe substitute as it came with its own warnings, its high cost and limited availability. I decided to give the FAC another go recently after seeing a recent social media post by fellow photogravurist Hervé Sachy and watching some YouTube videos by Habib Saidane. I sensitized a piece of Phoenix Gravure and made an exposure with a Stouffer 21 step, I transferred and developed it with success!

Test 1, Sep 8, 2023, Stouffer 21 Wedge, expose and transfer, no etch:
FAC 8%
Add oxalic acid to FAC sol. to PH 4 per Habib Saidane’s recommendation. This requires approximately 1g dry powder per 100 ml solution.
Please refer to SDS for oxalic acid and handle with care. The low concentration of the final solution is quite safe to handle.
Exposed Stouffer 21 250 LU (5x as long as my usual for Phoenix)
Transfer solution was distilled water and H₂O₂ 0.3% solution, chilled as usual for transfer. Mix H₂O₂ 1:9 with distilled water.
Stronger solutions of hydrogen peroxide oxidized the copper.
The exposed tissue was soaked for about 30 seconds in the cold transfer solution and squeegeed to the plate.
The backing paper was saturated with 60% alcohol and hot water development immediately followed.
Develop as usual in hot water. No H₂O₂ is required. This sensitizer and exposure did not yield many Stouffer steps so my next strategy was to drastically increase the FAC.
FAC is very soluble at room temperature to a factor of 100% and higher.

I also experimented transferring the exposed gelatin in cold water as usual and developing in an H₂O₂ solution but this produced no cross linking in the gelatin the way using a little H₂O₂ in the transfer bath did. The cross-linking of the exposed gelatin in dilute H₂O₂ is quite immediate.

Test 2, Sep 16, 2023 Pumpkin Blossom etch:
FAC 29% (added FAC to prev 8% sol)
Add oxalic acid to PH 4
Sensitized 2’ at 55ºF
Expose 150 LU both screen and image
Transfer solution was distilled water and H₂O₂ 0.3% solution, chilled as usual for transfer.
Etch 45-39.5 Baume
The etch did not really start until moving the plate into the 41º, at that point it is necessary to move back to a higher Baumé to avoid etching too fast.
Total etch time was 21 minutes.
The exposure was still too long as the etch stalled before the highlights would finish etching.

Test 3, Sep 17, 2023, Stouffer 31 etch:
FAC 29% (added FAC to prev 8% sol)
Add oxalic acid to PH 4
Sensitized 2’ at 55ºF previous day
Expose Stouffer 31 step 100 LU both screen and wedge (this is 2x my normal Phoenix exposure with standard 4% sensitizer)
Transfer solution was distilled water and H₂O₂ 0.3% solution, chilled as usual for transfer.
Etched in 45, 43, 42, 41, 40, 39.5 Baumé
The etch did not really start until moving the plate into the 41º, at that point it is necessary to move back to a higher Baumé to avoid etching too fast.
Total etch time was 19 minutes.
- This test yielded separation down to step 16 which indicates a transmission density range of 1.40 which is more than enough for photogravure positives. I will probably reduce my exposure further by a factor of 0.10 (1/3 F stop) shifting my D-max to step 15 which will net a density range of 1.30 and is still perfectly ideal for a full range of tones in photogravure.

• These tests show great promise for using FAC as an alternative sensitizer for photogravure with Phoenix Gravure or other gravure tissues. The methods are essentially the same as when using the standard sensitizer and the chemistry is also very safe and affordable.

• I can also see that FAC sensitizer and Phoenix can also be used for high contrast approaches like photo etching. Use lower concentrations (8%) and longer exposures in this situation. Film positives can be halftoned (laser copy on transparency, inkjet or imageset) or hand drawn such as ink on mylar, Sharpie on inkjet film, litho crayon or pencil on 3 mil matte mylar etc. Matte mylar films need 1.75 times the usual film exposure to make up for the film’s density. Always talc the crayon side before exposure or leave the crayon side up for exposure. Etch these plates in 41º or 40º Baumé ferric chloride. This simpler and safe approach could be a real gateway method for easing into the continuous tone etching process of photogravure.