FP4 35mm has blue base material?

During comparison of reversal processing results of 120 and 135 films I found that the 135 film suffers from a base tone that is slightly blue, thus giving colder image tone.

Complete processing was identical, so I wonder what makes the difference between the two otherwise identical films? Is it a processing failure? Or is it the base material of FP4 135? I had expected a neutral grey.

Hans Borjes said:

Complete processing was identical, so I wonder what
makes the difference between the two otherwise identical
films? Is it a processing failure? Or is it the base material
of FP4 135? I had expected a neutral grey.

Click to expand...

The 120 has a black paper backing while the 135 has
what is called an antihalation under coat on the film
itself; on the emulsion side but under the emulsion.

IIRC, if a pre-rinse is used and it is alkaline the blue
will turn to clear. If not alkaline, the pre-rinse water
will be blue. Test a roll with a bicarbonated and
another with a distilled water pre-rinse.

Bicarbonate is a weak alkali; water rinse prior to
developing. I suspect your film has been left with
minute amounts of the antihalation material. Dan

Hmm, I thought about antihalation layer as well. In the data sheet, Ilford mentions it for rollfilm and sheet film only, not for the 35mm film.

During which stage of reversal processing does the antihalation backing dissolve?

Are you speaking of the present day FP4+? Or the actual FP4 (no plus)? FP4+ is my main film, I shoot quite a bit of it in both 35 and 120, soup it mainly in Rodinal, never pre-soak (no particualr reason, I just never did - perhaps I will start...) and have found the colour of the resulting film base to be very neutral gray... I wonder why.

The 35mm film substrate, the plastic film base, on which the emulsion is coated is often colored to prevent light piping. This effect is different from halation. Light piping is the conduction of light sideways through the film during loading. The light enters the film from the tongue extending from the cassette and can fog several unexposed frames. Some plastic substrates are more prone to this effect than others. I believe mylar is worse than cellulose triacetate is this respect. Typical colors used are blue and purple although Plus-X uses a particularly foul greenish color. While the amount of coloration may not seem large when looking down on the base you must consider that the effect is cumulative for light passing sideways through the base. The dye is permanent and cannot be removed from the base material. This is in contrast to antihalation dyes which are in the emulsion and are water soluble. BTW, light piping is the reason why Kodak 35 mm infrared film must be loaded in complete darkness.

gnashings said:

Are you speaking of the present day FP4+?

Click to expand...

Yes, I do. Gerald's explanation sounds quite logical to me: if light piping is the reason to give the base material a coloration then 120 film does not need this protection, i.e. it can have a clear base.

Would be a good idea if Ilford put their 135 films on a clear base too to give these users the same superb material for reversal processing.

The only 35mm films that I know of with a completely uncolored base is one of the Maco films (Maco Ortho 25?) and, of course, Foma reversal film.

Gerald Koch said:

The only 35mm films that I know of with a completely uncolored base is one of the Maco films (Maco Ortho 25?) and, of course, Foma reversal film.

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Rollei R3 claims to have an entirely clear base, but I have not verified that.

FP4+ 135-36 has blue base!

I'm using FP4+ as Scala replacement. I asked Ilford why not using clear base for 135-FP4+ as used with 120-FP4+.

The answer is:
"...It would not be possible to change the base characteristics of FP4+ as the blue base is a specific design requiremnet of the 35mm version..."

It's not a bug, it's a feature. Well, for slide projection with a 250W lamp on 1.6m x 1m area it does not really matter. Just the image tone is a bit cool. When scanning a significant loss of contrast can be noticed. When processing with Tetenal Variospeed W instead of Rodinal the image tone is more like Scala including harder contrasts.

Dear All,

Gerald Koch is quite correct......normally miniature ( 35mm ) without a
coloured base is designed for a different use and just finished to 35mm,
and pretty sure to be on a polyester base.

Simon ILFORD photo / HARMAN technology Limited