Same Film, Different Dyes

[thuggins]

When you wash Ilford XP2 120 film, the wash water comes out a lovely shade of purple, I assume this is the antihalation dye. The wash water from 35mm XP2 comes out clear. This means they make a different base stock for the 120 and 35mm. That seems very inefficient from a manufacturing standpoint, so there must be some reason for it.

What possible reason would they have for two different formulations of the same film for a different size? If the antihalation was required (or at least beneficial) for 120 film, what harm would it be to have it in 35mm? Is this common with other films?

 

[MattKing]

The substrate (base) is actually different - from the Ilford datasheet:
DESCRIPTION
XP2 SUPER 35mm film is coated on 0. 125mm/5-mil acetate base and is available in 24 or 36 exposure DX cassettes, or in bulk film lengths of 17 and 30. 5 metres (56 and 100ft). XP2 SUPER 35mm film is supplied in DX coded cassettes, suitable for all 35mm cameras.
XP2 SUPER rollfilm is coated on 0. 110mm/4-mil clear acetate base with an anti-halation backing which clears during development. It is available in 120 lengths and is edge numbered 1 to 19. Following international standards, XP2 SUPER rollfilm has a red exposed label to signify colour negative processing.

 

[Mr Bill]

If you look at the clear base of same-name b&w film in 120-roll vs 35mm, you'll typically find that the 35mm has a "denser" (darker) base color. I think this is done mainly to help mop up light being "piped" through the film base. (Remember that 120 roll film never has the edge of film being exposed to ambient light.)

So perhaps the A-H dyes, or whatever, are able to be greatly reduced in the 35 mm film. Just a possible explanation. There are other ways to put in A-H, too; perhaps the 35mm film isn't using a dye. I'm sure there's other possible explanations, but I don't want to go too far out on a limb with my guesses.

 

[AgX]

-) there is that different light-piping issue. BUT a dyeing of the base itself also is one anti-halation means, which is benefitial for all types of film (aside transparency films).

-) rollfilms often have a anti-curling backing layer. A manufacturteer may be tempeted to combine this with an anti-halation dye to save coating it on the "proper" AH location.

 

[WilmarcoImaging]

Yes, in a manufacturing setting, if everything is the same, cost (scale of material purchase) and efficiency (fewer or absence of changeovers) and therefore profits are improved.

Possible reasons for the different base material:
- 135 size film requires slitting to a narrower final width. The slitting process may be favored by thicker base material.
- 135 size film requires sprocket hole punching. Same comment as slitting.

 

[DREW WILEY]

35mm film is rolled back up in a cassette, fully protected from light. 120 film isn't, so ideally needs a stronger antihalation dye and backing. If you want a horror story, a friend and I had just returned from a two-week high altitude backpacking trip that involved a lot of steep off-trail travel with heavy packs. We were both shooting Efke 25 120 film, which certainly has less than ideal antihalation properties. When we finally got back to our cars one night, he wanted to sort out his exposed film spools end-on in a box, so put on his bright halogen headlamp to do it. Over half the rolls were fogged and ruined. He knew to be careful changing film during the day, and looked for shade, but at that moment learned a hard lesson.

 

[AgX]

35mm film is rolled back up in a cassette, fully protected from light. 120 film isn't, so ideally needs a stronger antihalation dye and backing.

Antihalation means only are directed at light from sources within the image. But as I indicated with the base dye it can serve the other means of preventing light piping through the leader too.

Type 120 has no film leader, the long edges are covered too, thus there is no light piping issue.

 

[darkroommike]

Yes, in a manufacturing setting, if everything is the same, cost (scale of material purchase) and efficiency (fewer or absence of changeovers) and therefore profits are improved.

Possible reasons for the different base material:
- 135 size film requires slitting to a narrower final width. The slitting process may be favored by thicker base material.
- 135 size film requires sprocket hole punching. Same comment as slitting.

35mm film was originally engineered to be "jerked" through a movie camera and then a projector so it is a little "beefier".

 

[thuggins]

While cutting and sleeving the film, I noticed that the 35mm has another interesting peculiarity. In the border, along with Ilford XP2 Super and frame numbers, it says Safety Film.

That certainly put my mind at ease.

 

[DREW WILEY]

AgX ... No light piping issues??? Ha Ha Ha Ha. There must be a reason every roll of 120 film comes with the warning, Load in subdued light ! I don't know exactly what your definition of piping is, but leaky pipes can sure be a problem.