Hi, just to confirm that I am understanding, let me restate: you are setting enlarger exposure to just barely give a visual "black" on the print when exposing through a clear, unexposed piece of film. Then, when you use this same enlarger exposure with a real negative, the parts that should print black, or nearly so, actually print much lighter. (Do I have this correct?)
This is a mistake a lot of people make - it will not give you an accurate time because the frame will not have received in camera flare, related processing fog, etc. To test for minimum black, you need a frame that has been accurately (i.e. you have tested for your personal EI with the camera, lens, film and developer that you plan to use) exposed at Zone 0 AND have determined the minimum print development time to achieve a good black.
You use the Zone 0 negative to do one test strip (at grade 2 for a condenser enlarger and at grade 3 for a diffusion/multigrade/colour head enlarger) to identify roughly what is the minimum exposure time to achieve black will be. Then do a series of 5 small test prints where you expose each of them for double the time you identified as being the rough minimum exposure (i.e if your very first test indicated 10 seconds then expose the 5 test prints for 20 seconds). Number the test prints on the back from 1 - 5 and then develop them for 1 minute, 2 minutes, etc. Give the prints your normal fixing and give them a quick wash and then dry them (this is very important for FB paper and the easiest way of doing this quickly is to get a cheap second-hand microwave oven and use this to dry them).
Line the 5 prints side by side with the print with 1 minute development to the far left and the print with 5 minutes development to the far right. Now comes the key part of the test, look at each test print and identify which print has a maximum black. Usually, you will find that (with FB) the one with 1 minute development will look OK until you compare it to the one with 2 minutes development which will look darker, etc. Then repeat until you find the print that is darker than the one to its left but the one to its right is not any darker. The print that does this is your absolute minimum development time to achieve a true maximum black. You can always develop for longer than the minimum for the purpose of changing tonality, etc but never less.
In general, with the discontinued Polywarmtone, the discontinued Adox FPVC, the discontinued Kentmere FPVC and the current Foma Variant III and Adox MCC 110, I have found that, irrespective of a ± 5˚ degree variation from 20˚C, all of them require at least 3 minutes when developed in Tetenal Dokumol 1 + 6 to fully achieve a real black.
Now that you have found the required time to get a good black you can move forward with some more 'real world' tests. Take a negative and expose it for the exposure and development time that you have found is required for achieving a good black.
- If the subsequent print has too little detail in the highlights then you will have to burn in your highlights (this means giving more exposure to the highlights in your image) or reduce the contrast setting on your enlarger.
- If the subsequent print has too much detail in the highlights then you will have to dodge your highlights (this means giving less exposure to the highlights in your image) or increase the contrast setting on your enlarger.
Now you are getting near to a good print and will have learnt a great deal about manipulating the tonal range of your prints.
If, for example, you are now happy with the print overall but unhappy with the separation of tonal values in the darker shadow areas, this will indicate that your shadow areas require the use of a higher grade of contrast to achieve the required separation that you would like and this will then necessitate you burning in your highlights (this means giving more exposure to the highlights in your image) and/or reducing the contrast setting on your enlarger. when burning in.
Once you are happy with the result, you can then determine the following:
- If, using the maximum black exposure, your print looks fine then you have truly fixed all of the variables.
- If, using the maximum black exposure, your prints are always too grey, you need to increase the development time for your films.
- If, using the maximum black exposure, your prints are always too contrasty, you need to decrease the development time for your films.
- If, using the maximum black exposure, your shadows are consistently too light, you are overexposing your film and will need to adjust your E.I.
- If, using the maximum black exposure, your shadows are consistently too dark, you are underexposing your film and will need to adjust your E.I.
It all sound damned time consuming I know. However, in reality it does not take very long to do and you will have pinned down all the major variables so that you can abandon further testing and get on with making photographs.
Bests,
David.
www.dsallen.de