Kallitype contrast control
I have a question about contrast control with the kallitype process. I know it has been discussed here in passing, but I am still a little confused. When I first began making kallitypes, I followed Sandy King’s excellent article posted on unblinkingeye.com. I believe there is some mention of the ability to control contrast in the article, but he does not elaborate. He recommends a negative with a DR of 1.8. Makes sense.
I recently stumbled on another version of this article at alternativephotography.com where contrast control with the addition of potassium dichromate is discussed in greater detail:
“Contrast can be controlled by the addition to the developer of a few ml of a 5% solution of potassium dichromate solution. The practical limit ranges from as little as 1 ml per liter of developer up to about 16 ml per liter. This allows the use of negatives from a DR as low as about 1.2 to a maximum of about 2.2. If too much dichromate is added, printing times will increase considerably and the image will take on a granular look. For negatives that have been developed to a DR of about 1.8 add about 2ml of the 5% potassium dichromate per liter of developer.”
[After posting, I noticed that this paragraph appears in both articles, but I only see the recommendation for 2 ml with a 1.8 DR in the alternativephotography.com article.]
What I am wondering is this:
I was under the impression that a negative with a DR of 1.8 was appropriate for use with straight sodium citrate developer with no contrast agent additions. If it is recommended that one add 2 ml of potassium dichromate when using a negative developed to a DR of 1.8, does this mean that with straight developer a kallitype requires an even denser negative? Is this what is meant by “a maximum of 2.2”? In other words, shoot for DR of 1.8 with 2 ml of potassium dichromate, but if you miss that target and overdevelop you can skip the dichromate; and, if your negative is too thin, you can add more dichromate?
And last, but not least: does anyone have the DR numbers for a given quantity of dichromate per liter of developer, or is there a certain amount of trial and error with this?
Last edited by Paul; 09-11-2006 at 03:51 PM. Click to view previous post history.
Originally Posted by Paul
First, some small amount of dichromate is needed with kallitype, even with negatives of optimum DR, which is about 1.8, to completely clear the paper. The same is also true with straight palladium, where you need either a bit of platinum, peroxide, Na2 or dichromate to clear the last bit of stain.
As for the amount of dichromate needed to adapt the negative DR to the process, here are my figures. However, it would probably be better for you to get a Stouffer TP 45 test step wedge and test for your own conditions since choice of paper and chemistry can change matters a lot. However, assuming a 5% solution of potassium dichromate, here is what I would add to a liter of developer for needed DR control.
Negative DR Amount of Dichromate per liter
1.2 16ml (but dangerous to go there because of grain)
These are real figures based on my work, but use them as a guide and best to test your own materials.
Thanks so much. That answers all my questions in one neat package!