Question about Film backing materials

[Pirate]

I've noticed that Arista EDU Ultra 100 has a Blue backing while others have more Brownish and some have a slight dark tint, but I've not seen one that's clear.

I've learned a lot over the past few years but this is something I've not gotten into yet.

Can anyone please explain the different backing layers to me? Why the different colour tint? What's used for what??... etc. It seems that the Blue backing is well suited for portrait work for sure.

Thanks

 

[Fotohuis]

Arista EDU Ultra 100 aka Fomapan 100 has a Blue tint for the roll film version. The emulsion for 120 roll film of all Fomapan films has been made on Blue Polyester which is part of the anti-halo layer. Another method is to coat an A.H. layer seperately. The Rollei films (except RPX100/400) are also made but on clear Polyester layer. They have a seperate A.H. layer and due to the clear Polyester you have to load and unload them in subdue light.
Efke also changed a few years ago to clear Polyester for both 35mm and roll film, so it's about the same.

 

[sevo]

What backing? In general film is made up out of the photo sensitive layer(s), anti-halation layer, bonding layer, carrier base and in the case of medium and large format of another bonding layer and backing layer. All of which may have tints, for different reasons.

The anti-halation layer is a dyed gelatin layer between base and film to prevent light going past the sensitive layer and scattering from the base or pressure plate. 120/220 and large format film has a additional backing layer at the rear of the base to improve planarity - this often is dyed like the anti-halation layer (for no better reason than that it is often applied in the same dip coat process as the anti-halation).

The base may be slightly grey pigmented to prevent light piping from the film edge - a requirement on 135 film with its protruding leader, as clear base film has to be dark loaded. Roll and sheet film does not need a base tint, as light cannot enter it from the leader edge (sheet not having a leader, 120/220 having a paper leader) - often the base is tinted nonetheless, to reduce the number of base types required, and to limit the damage done by light leaks.

Film may also have a tint due to residual sensitizing dyes in the light sensitive layers - Kodak T-Max can be quite vividly pink right after processing, but that fades soon.

The backing colour you see may be a matter of the dyes used for a technical reason, or of de-facto branding (makers probably didn't initially pick a colour as a intentional decoration, but it would be poor brand management to switch it at random later on).

 

[Pirate]

Thanks guys, I think that explains what I was looking for.

I love this place for all the information!

 

[Freakscene]

What backing?

In the case of this Foma-made film, it is the film base itself that is blue, and this colour does not change after processing.

Marty

 

[Pirate]

Yes, I goofed my terminology a bit 😀