Looking at the “literature” on cyanotype, there are reports of acid affecting the outcome at two points in the process. One of these points is the pre-treatment of paper to remove the calcium carbonate “buffer” present in many papers not specifically made for alt process printing. The second place that acid enters into the ‘equation’ is during development of the print. It is reported that using vinegar gives better mid-tone contrast compared to water.
My normal practice in making cyanotypes using the traditional sensitizer is to use papers as they come out of the package (i.e. no pre-treatment before coating) and to develop cyanotypes using 25% (v/v) vinegar as developer.
I have been quite satisfied with prints made this way, but given the repeated mention of acid pre-treatment I decided to experiment in order to see the effect for myself. In addition, I had never done a direct comparison between using vinegar and water as developer so I added this to my experiment.
Paper was acidified by soaking it in dilute hydrochloric acid for three or four minutes, washing the paper in water for about 5 min and air drying it. I used concentrated hydrochloric acid (HCl) (i.e. “muriatic acid” sourced from the hardware store; the label reads “20 degrees Baum/31.45%”) and diluted it 1:10 with water (i.e. 100 mL in 1L total volume). Remember to always add acid to water and not the other way around! The resulting solution is about 1 molar.
The first paper I treated was Stonehenge Warm. Evidently this paper is heavily buffered. I could see numerous bubbles emanating from the paper upon placing it in the acid and putting my ear close to the tray I could hear it fizzing! I also treated two other papers: Hahnemuhle Biblio and Fabriano Artistico (hot press). Both of these papers reacted similarly to the acid however the reaction was not as vigorous as with the Stonehenge Warm.
After the acid treated papers were dry, I coated these sheets, as well as some untreated paper, with the traditional cyanotype sensitizer.
For my first experiment, I exposed four sheets of the Stonehenge Warm paper (two untreated and two acid treated) under the same negative for eight minutes. One pair of sheets was developed in 25% (v/v) vinegar and the other in plain water.
The results shown in Figure 1 (compare the two images in the left column) clearly show, as others have reported, the improvement in mid-tone contrast using vinegar as developer. Additionally, these results clearly show that pre-treating the paper with acid increases its sensitivity to UV light after coating.
The latter result is not entirely unexpected as I have noticed in the past that unbuffered papers made for alternative processes (such as Arches Platine and Hahnemuhle Platinum Rag) generally require less exposure to make an acceptable print than do other papers.
Figure 1
In order to better ascertain the effect of acid pre-treatment on print quality, I made a second set of exposures in which, aiming for a similar Dmax on pre-treated and untreated paper, I used shorter exposure times for the pre-treated paper than that used for the untreated paper. I used two different papers for this experiment Fabriano Artistico (hot press) and Hahnemuhle Biblio. Again, the same negative was used for all exposures.
The results are shown in Figure 2. Prints made on untreated paper (left column) show somewhat higher contrast than those on paper pre-treated with acid (right column).
Figure 2
My conclusion from these tests is that I will continue my usual practice of coating “straight out of the package” paper with traditional cyanotype sensitizer and developing images with 25% (v/v) vinegar.
Looking at the overall quality of these prints, at least in my hands, the added complication of pre-treating paper with acid is not warranted. However, the minimal cost (both financial and temporal) of using vinegar in place of water for development is reasonable.
I hope that this information is useful to someone other than myself!
Regards,
--- Frank Gorga (www.gorga.org/blog)
My normal practice in making cyanotypes using the traditional sensitizer is to use papers as they come out of the package (i.e. no pre-treatment before coating) and to develop cyanotypes using 25% (v/v) vinegar as developer.
I have been quite satisfied with prints made this way, but given the repeated mention of acid pre-treatment I decided to experiment in order to see the effect for myself. In addition, I had never done a direct comparison between using vinegar and water as developer so I added this to my experiment.
Paper was acidified by soaking it in dilute hydrochloric acid for three or four minutes, washing the paper in water for about 5 min and air drying it. I used concentrated hydrochloric acid (HCl) (i.e. “muriatic acid” sourced from the hardware store; the label reads “20 degrees Baum/31.45%”) and diluted it 1:10 with water (i.e. 100 mL in 1L total volume). Remember to always add acid to water and not the other way around! The resulting solution is about 1 molar.
The first paper I treated was Stonehenge Warm. Evidently this paper is heavily buffered. I could see numerous bubbles emanating from the paper upon placing it in the acid and putting my ear close to the tray I could hear it fizzing! I also treated two other papers: Hahnemuhle Biblio and Fabriano Artistico (hot press). Both of these papers reacted similarly to the acid however the reaction was not as vigorous as with the Stonehenge Warm.
After the acid treated papers were dry, I coated these sheets, as well as some untreated paper, with the traditional cyanotype sensitizer.
For my first experiment, I exposed four sheets of the Stonehenge Warm paper (two untreated and two acid treated) under the same negative for eight minutes. One pair of sheets was developed in 25% (v/v) vinegar and the other in plain water.
The results shown in Figure 1 (compare the two images in the left column) clearly show, as others have reported, the improvement in mid-tone contrast using vinegar as developer. Additionally, these results clearly show that pre-treating the paper with acid increases its sensitivity to UV light after coating.
The latter result is not entirely unexpected as I have noticed in the past that unbuffered papers made for alternative processes (such as Arches Platine and Hahnemuhle Platinum Rag) generally require less exposure to make an acceptable print than do other papers.
Figure 1
In order to better ascertain the effect of acid pre-treatment on print quality, I made a second set of exposures in which, aiming for a similar Dmax on pre-treated and untreated paper, I used shorter exposure times for the pre-treated paper than that used for the untreated paper. I used two different papers for this experiment Fabriano Artistico (hot press) and Hahnemuhle Biblio. Again, the same negative was used for all exposures.
The results are shown in Figure 2. Prints made on untreated paper (left column) show somewhat higher contrast than those on paper pre-treated with acid (right column).
Figure 2
My conclusion from these tests is that I will continue my usual practice of coating “straight out of the package” paper with traditional cyanotype sensitizer and developing images with 25% (v/v) vinegar.
Looking at the overall quality of these prints, at least in my hands, the added complication of pre-treating paper with acid is not warranted. However, the minimal cost (both financial and temporal) of using vinegar in place of water for development is reasonable.
I hope that this information is useful to someone other than myself!
Regards,
--- Frank Gorga (www.gorga.org/blog)