Printing Color C41 (Negative) Film in the Darkroom

As I started to write my post on Chromogenic film I realized I was digging deeper into the whole subject of printing C41 negatives and the reason why Chromogenic black and white film exists. It just so happens I had finished a couple of rolls of film in my Mamiya 645 Pro. 

These rolls violated one of my rules of mixing color and black and white shooting in the same session. The great thing was I had some photos of the same subject taken back-to-back on both black and white film (Ilford HP5+) and color negative (Kodak Portra 400). 

Here is the color version. 

When I first got into film photography (over 10 years ago!) I preferred reversal (slide film) over color negative film. I had struggled to get good colors with scanned negative film. Eventually I learned enough to know how to get good color correction on color negative scans. After I came back to color negative film I thought an added benefit of C41 negatives would be to be able to make black and white prints in the dark room without the need for internegatives. Now I can try this out. 

I started out with some birch trees I shot at Holme Fen. The only difference between the two is the film and a slightly different composition because they were handheld shots. I printed these all on 8x10 Kentmere VC Select which is an economy multi-grade RC paper made by Ilford. 

First came test strips. Here one can begin to see the differences. I made a soft filter (#00) and hard filter (#5) strip for each negative. The black and white film was at f16 while the C41 (Portra 400) was at f8 which reflects the attenuation due to the orange mask of the color film. From bottom to top the exposures are 8, 11, 16, 22, 32, 45, 64 seconds. The hard filter shows more contrast with the Ilford black and white film.

Test Strips
(C41 Soft, C41 Hard, HP5+ Soft, HP5+ Hard)

Next I printed the HP5+ film getting very close to what I wanted with #5 32 seconds, and #00 11 seconds.

Ilford HP5+

Next I made a series of prints on the Portra 400 negative as I strove to make a print as close as possible to the one above. This is not good it is dark and lacks contrast. 

Porta 400 #5 45 seconds #00 11 seconds.

This next one was much lighter with 1/2 stop less on each filter.

Porta 400 #5 32 seconds #00 8 seconds

 Still the blacks want punching up so the next one I upped the hard filter 1/4 stop. 

Porta 400 #5 38 seconds #00 8 seconds

This is close and actually not a terrible print. Below I make a side-by-side comparison with the HP5+ negative and the better contrast control is evident. It is easier to get a strong black and preserve the white bark of the trees with the HP5+ black and white negative. 

Ilford HP5+ (left) vs Portra 400 (right) 

The natural question is why not throw out the soft filter altogether to get more contrast. So here it is 4 versions of the Portra 400 mage with no soft filter and increasing hard filter by 1/2 stop. 

No Soft Filter Portra 400
(Clockwise from upper left: #5 38 seconds, 45 seconds, 54 seconds, 64 seconds)

Here there is nothing that is quite the same as the HP5+ print; the lower right corner is perhaps closest but the blacks are not as black so if high contrast is what you are after you are going to be unhappy. The highest exposure on the lower left has comparable blacks are the expense of the muddy highlights. We can see this in their respective histograms...

Histogram Comparisons
(upper four same position as Portra 400 prints above, bottom is HP5+ print) 

In all print scans the only adjustment I did was set the white point from the lower right corner of print border. I did not adjust the black point or expand the range. The spike on the right (white) is the included border. 

Increasing the exposure gets closer to true black but the distribution of tones is more bunched to the black end of the scale so all the tones are dragged up. The bottom histogram of the HP5+ print shows how the tones are more distributed across the range. Remember also that I left in 11 seconds of the soft filter on this print so there is more room for higher contrast. 

Why the Difference?

Next I try and figure out why the results are poorer with the C41 negative. First we should review the way multi-grade paper works. Basically the emulsion consists of multiple layers with sensitivity to blue and green light. All layers are sensitive to blue light but when exposed to only green light some of the emulsion reacts more slowly and this makes for a transfer curve that is less steep. The curve for blue light has a steeper curve. By varying the exposure to change the mix of blue and green light the slope or steepness of the curve can be varied. 

Because the curve relates density in the paper versus relative exposure, areas of the negative with more light passing through (shadows) gains density (becomes darker) much more rapidly for blue light compared to green light. 

Multi-grade Paper Transfer Curves
(From Ilford...)

When we look at the filters in the multi-grade system they range in color from Magenta (Hard) to Yellow (Soft) not blue to green. The reason for this is that the paper is blind to red light (hence the reason a red safelight does not fog the paper). So the filters pass the color red as well as blue and/or green. Red + Blue = Magenta, Red + Green = Yellow. This makes the filtered image on the easel easier to see as the eyes get more light than if the filters were blue or green alone.  

If we then look at a scan of the negative we might analyze the problem. Below is the full color of the negative. The strong orange color is the mask filter layer. It is the source of most of the problems. Firstly it adds a layer of attenuation hence the reason I need 2 stops more light to get a similar exposure compared to the HP5+ negative. 

Next I stripped all the red color from the negative because we know the paper will not react to red light. Now have just blue and green left as an imitation of what the paper can see. If we look carefully at the leaves we notice they are almost entirely blue which means they will turn up very dark. 

Next I remove the green color to show only the blue. The first thing we notice is that the overall blue image is very dark. That may be ok and is part of why more exposure is required. If this were the only problem then we could just up the exposure to get the desired density. There is blue image information so all should be well.  (But we know it isn't.)

Finally we look at the green only channel. Green produces the lowest contrast as it takes longest to build up density on the paper. Again we can find some green image information so we could manipulate the exposure through the soft filter and get a desired lower contrast version. 

If we look at this through the corresponding histograms we begin to see the problem. I have shown four histograms below the blue, green, green+blue, and all color versions. 

Blue, Green, Blue+Green, and Red+Green+Blue Histograms (left to right)

If we look across the blue and green channels we see a relatively little range of tone represented. This isn't surprising in some sense as the image does not have many colors. The image is also relatively low contrast and more so when we constrain the colors available. The histogram on the right shows the full range for all colors and red brings in the hump on the right which is a lot of the luminosity on the negative.  

Clearly this changes with the colors in an image but the sensitivity is inverted. For instance printing on paper which is red blind is like taking a black and white photo with orthochromatic film however because of the color inversion in C41 film red in the scene will render as cyan on the negative which will print because cyan is a combination of  green and blue. Conversely the film will appear blind to cyan which will be rendered as red on the negative and this will not be seen by the paper and thus will appear white. 

Printing on Pan-chromatic Paper

Many people will claim that pan-chromatic paper does not exist anymore. Kodak made Panalure but the one box I could buy was old and thus badly fogged. I did discover however that Ilford makes a product called Galerie RC Digital Silver which is made for machine processing on color digital enlargers. As such it needs to react to red, green, and blue LEDs or lasers used in these machines.  

If we look at the Kentmere vc Select paper sensitivity curve we see this response. 

We can compare it to the Digital Silver sensitivity... 

In both graphs I overlaid the color scale to better visualize the color range. This extends much further in to the red sensitivity. The Digital Silver paper is only sold in rolls as it is meant for machine processing. I did find that Photowarehouse in the US offered cut sheets in 8x10. I did not have much luck. The first batch was entirely black and I suspect they cut it under safelights. 

They replaced it for free of charge but I had to wait a year for my next annual trip to the US. The replacement box however has a faint gray band of fog over the every sheet as far as I can tell. They seem to be selling this now as their own panchromatic pinhole paper cut to sheet film sizes. Still it can be used to understand if this helps at all. It is a single grade or contrast however so you have to take what you get... 

A couple of stabs at an aperture landed at f8 for a test strip. This is with no filtration. 

Panchromatic Paper Test Strip
(f8 8-64 seconds 1/2 stops. Note gray vertical band near center, a fault on every sheet.)

Already you can see there is not much contrast. I pick 22 seconds (4th from bottom) as reasonably good and make a print. (Recall all these examples will have a faint vertical band due to handling problems when the sheets were cut and boxed.)

Panchromatic Paper Print (f8 22 seconds no filter)

What can I say. Low contrast and too muddy for the subject matter. It might work for some images. 

C41 Multi-grade vs Pan Paper Comparison

Next I experimented with further filtration. I don't have an extensive set of filters however. It was interesting to try the red safelight filter with this paper. 

Panchromatic paper printed with red safelight filter

I tried hard and soft filters as well and the results were not much different as they both admit red light in addition to blue and green light respectively. Next I tried to make a green filter by stacking some color printing corrective filters (+.5 cyan + .4 cyan + .5 yellow + .4 yellow) this resulted in a very dim test strip by about 2.5 stops. This is not surprising as the color histogram of the green channel indicates not much light passes in green only. 

Panchromatic paper printed with green filter

If you have made it this far you should probably have something better to do! There seems to be no way to redeem the panchromatic paper or printing C41 negatives on black and white paper. If you must then multi-grade paper gives the most hope of controlling contrast. There are other areas to explore including higher contrast development techniques such as VGT developer from Moersch Photochemie, lith printing, and pulling from the developer early before the highlights get fully developed. 

Addendum: Making an Interpositive?

Recently on Reddit there was a question about making a black and white interpositive as a means of printing a C41 negative on black and white paper. I suggested how this might be done and mentioned that orthochromatic film is easier to work with in the darkroom owing to being safelight compatible. Someone pointed out that the tones would shift if this was the case. For instance greens would look lighter. Using the images from this post I mocked up with Photoshop what a print might look like on an ortho vs panchromatic film interpositive.  

I took the full color negative scan from above and made two versions one with the red channel stripped and the other untouched. I then desaturated each image and inverted them. I then ran the Levels function in Auto to adjust the black and white points and center the histogram. The results I have below. They confirm the greens are lighter for the ortho version. Now it seems I have something to try as yet another project. 

Removed red (left) version vs full spectrum (right)