In an interesting and timely development, HP has released a paper preset for their Z3200 large format printer line to make the production of digital negatives for alternative chemical photographic processed, like platinum and palladium printing easier.
This is timely indeed, because of a rise in interest in what is called alternative printing processes and I highly commend HP to taking this step. Photographers need all the options they can get and anything that makes this easier is a wonderful development.
Apart from the preset, HP has produced an excellent PDF of the process. Let me quote from it about how their preset works: “The process described here was performed with the goal of creating feasible negatives for monochrome and color alternative process such as platinum/palladium, carbon, cyanotype, gum, carbro, multicolor carbon, and tri-color gum” and then “From a technical point of view, what is inside this preset is a green ink separation that has been linearized in terms of ultraviolet light opacity. The advantage of having this linearization is that when printing a linear ramp of green ink values with this paper preset, the result will be a negative with a near-linear response in any alternative process based on UV light. In certain cases, some calibration may provide additional improvements. However, the tools needed to perform this calibration are part of the standard printer software and hardware.”
This further quote from the same PDF makes the process clear to those used to alternative process printing:
“In this solution, the green ink acts as a color filter for ultraviolet light. The densest part of the negative contains a maximum quantity of ink. This maximum ink must be able to block UV light in such a way that the paper will be left blank after exposing it trough this maximum ink combination. In order to reach a maximum level of opacity, which will be different for every process, black ink is combined with the green one.
When a RGB image is sent to the printer, the Green channel in the image will be used to form the final negative and the Red channel will be used to control opacity using Black ink. Think of the Red channel as a kind of red filter that will control the maximum opacity of the negative.
To find out how much black ink is needed in your process, a form of calibration process needs to be performed first:
- First, the correct exposure time for your process using your film must be determined. This exposure time is also called the standard printing time. This time is calculated by making a test strip using a piece of the negative film substrate. Every strip must contain a portion of film substrate and a portion of paper not covered by the film. The exposure time where the achieved black under the film is the same that you have on the paper will be your standard printing time.
- Then a calibration strip must be printed using your standard printing time to know which quantity of black in combination with green will yield a clean white on the paper.”
Most of the alternative processes rely on UV exposure, either from the sun or from an artificial light source, to actually produce the chemical changes in the paper coating that you apply. Since HP know the exact UV characteristics of their inks they are the right people to achieve this and do so accurately.
For more information about this I can recommend the following sources:
- A HP article about the production of platinum prints for Elliot Erwitt
- The PDF document of the whole process
- A video on Youtube of the process
A big well done to HP, especially given that their process supports the use of non-HP media, such as the Premier Imaging Products film and the often used Pictorico OHP one. It seems like it should work with other clear films too.
I’ll be incorporating this into the workshop I run on digital negatives.