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I'm doing my Bachelor's degree from photography. I noticed that my developed film Ilford HP5+ is not just black&white but it is slightly violet (as you can see on the left picture). Does it have anything to do with fixing time? I tried to find the literature why this happened, but didn't find any.

Ilford HP5 isn't black and white

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    Are the prints slightly violet, scans from the negatives, or scans from prints? Is it possibly due to a minor fluctuation in the color of the film itself? (the film backing, not the photosensitive chemicals in the emulsion.) – Michael C Jun 9 '16 at 11:08
  • Scans from negatives. – Piipsy Jun 9 '16 at 18:06
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    Any color cast in a scanned file from a monochromatic source is 100% user error, if you are getting color casts then you are using the scanner improperly. You should adjust the white point and scan in grayscale when you are using monochromatic sources, or grayscale+IR if you are using monochromatic but chromogenic sources. – Dietrich Epp Jun 10 '16 at 5:32
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Its been a very long time, but I believe this is caused by inadequate rinsing of the negative during processing. The film has a coating to reduce light reflecting from the film backing itself. It is usually rinsed away, but seeing a slight purple tinge on negatives is likely very familiar to those who have developed their own B&W film. The coating is called 'anti-halation' coating.

As others have said, it does not impact the print image itself, since B&W paper can not reproduce 'purple'. If you are printing on a color inkjet printer from a scan, it may be reproducing the purple, since most CMYK inkjets simulate B&W using a mixture of CMYK inks (not just the K). A solution is to convert the image to B&W in your editing software, or use B&W/greyscale inkjet ink pots.

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    I agree, especially if the tint is visible when looking at a clear area on the physical negative film. There is a chance that it might just be a color balance issue when scanning in RGB mode. – David Rouse Jun 9 '16 at 13:49
  • I'm talking about scans from negatives, not printed images. I'm not searching for the solution, just for the explanation - I need to write about this in my BA. – Piipsy Jun 9 '16 at 18:08
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The color of a B&W negative is irrelevant unless you're using color print paper. If you have true B&W paper, then all that it cares about is the relative irradiance. You could print with any color negative and get a B&W image. If your print is what appears to be tinted, then either the paper is not what you think it is (e.g., there are styles which produce sepia-toned prints) or it's ancient and expired, or you've introduced a color overtone from some problem with the chemicals.

  • I need the explanation for my Bachelor's Degree. I have a scanned photo that turned out slightly violet and I need to find out why. The photo wasn't developed at home so I wouldn't say there was a problem with chemicals. – Piipsy Jun 9 '16 at 18:04
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    @Piipsy "The photo wasn't developed at home so I wouldn't say there was a problem with the chemicals". As a person who used to develop photos for people at a major chain, the fact that it wasn't developed at home to me makes me think a problem with the chemicals is more likely, not less. It's also possible color paper was used because who wants to unload and reload with B&W paper (assuming any is even available) when the negatives are B&W already. "Professional photo processing" available at major chains is basically the fast food of photo processing. I was sixteen when I had that job. – Todd Wilcox Jun 9 '16 at 21:44
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    Oh I just remembered that people would absolutely bring in C-41 process B&W negatives and we would run them through the developer along with the C-41 color negatives and then print them on the exact same color paper we used for color prints. We definitely had no B&W paper. The only time we changed paper was to switch between 4x6 and 3x5/5x7 size stock. Us teenagers who knew very little about photography or chemistry were trusted to replenish chemicals in the machines - although normally that was simple because the whole bottle was pre-measured. You probably just got color paper. – Todd Wilcox Jun 9 '16 at 21:50
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Each manufacturer uses a slightly different film base. Ilfords is slightly purple, Kodak's slightly cyan on some and Agfa had a slight green cast. This changes by film type as well within a brand. The color can impact the print if you use Variable Contrast paper. Fixing isn't usually a problem related to film base color. Kodak's Tech Pan was the most neutral as I remember. Most of the films I used are no longer available.

  • I'm trying to find some literature (proof for my BA) about Ilford being slightly purple, but don't find any. I found this statement just for Tri-X. – Piipsy Jun 9 '16 at 18:12
  • @Piipsy - the color is shown on positive, i.e. reversed image. If it was reversed as RGB, the negative color would be also reverse from purple, i.e. green – MirekE Jun 9 '16 at 18:17
  • Orthochromatic film was completely clear. It was on a PET base. Sound recording film and Shellburst, Rapid Access was also on a clear base. – Stan Jun 10 '16 at 5:30
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Early photo materials were not very sensitive to light. Additionally bright objects often imaged as a blurred splotch. This imperfection is called a halation. The solution is various colored dyes applied during manufacture. Dying light sensitive silver salt crystals changes their sensitivity and adjusts how they react to different colors. The problem of the halation is solved by an undercoat of dye. This dye is the color the film is least sensitive too. A UV blocking overcoat is also applied.

These sensitizing dyes and anti-halation dyes are generally water soluble. Therefore they will wash away during the processing steps. Some, however, are stubborn and these linger. They will eventually wash out given time. These give the processed film a tint that is uniform thus harmless. The main effect is cosmetic. If you are making chemical prints, the dyes block some blue exposing light -- thus they add a smidgen of extra print time.

If you are a purest who hates the coloration these dyes can induce, then add time to the fix and or the wash stage to give further time so they can wash away.

The breakthrough came in 1873. Hermann Vogel, Professor at Berlin Technical, wanted to solve the halation problem. He reasoned that light was being reflected within the emulsion. He has a student dye an emulsion yellow. This prevented the halation. To his surprise the emulsion gained green sensitivity. Over time, his graduate students experimented with sensitizing dye and gained sensitivity to red.

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During exposure light travels through emulsion, bounces back from the backing layer and exposes the emulsion again, this time with blurred light, adding halos to the image.

This reflection can be prevented by adding opaque dark layer behind the emulsion. Due to the nature of b&w films, the layer is made of soluble dye.

Most of the dye is removed during processing, but usually not all and some residual coloring is normal. Amount of the coloring will vary depending on used processing chemicals and time of processing. You don't see this coloring with other types of films, because they use silver based or pigment-based anti halation layer that is not possible with b&w negatives.

  • All of the nonhalation coating is removed during processing by the fix bath; but, there are also dyes added to the actual film base in many cases. "Anti-halation" was coined by Kodak for the generic term. – Stan Jun 10 '16 at 5:34

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