What chemical for anti reflection coating that dissolves completely?

[rwhb12]

I have always wondered what is used on film backing as it liquefies completely in contact with water, leaves no stain or residue, yet must do a good job of preventing light piping and reflections. Can someone enlighten me?

Russ

 

[Gerald C Koch]

Do you mean the anti-halation coating?

 

[AgX]

Well, the antihalation coating is an anti-reflection coating, with halation being caused by reflection.
Though it can serve other purposes too.

Several different systems are employed. Furthermore aside of a coating of the backside of the film base a coating inbetween the film base and the emulsion is employed

 

[Gerald C Koch]

Light piping is caused by light entering the edges of the film base. This is a problem with 35mm file but not other formats. To prevent this a dye is encorporated into the film base. This dye does not wash out as it is part of the plastic base. The amount of light piping is a function of the type of plastic. Estar (Kodak tradename for polyester) based film is more prone to light piping than is acetate based film.

 

[rwhb12]

Thanks for replies so far.

 

[kevs]

Dyes are generally used, but Kodachrome and movie films use(d) a carbon coating called rem-jet on the back . Dead Link Removed