Question for the darkroom guys. Re: Remjet

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Question for the darkroom guys. Re: Remjet

Postby Actor » Sat Aug 15, 2009 7:38 pm

What is the difference between remjet and anti-halation layer? Or are they the same thing?
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Re: Question for the darkroom guys. Re: Remjet

Postby Janne » Sat Aug 15, 2009 8:20 pm

Rem jet is a black coating on the back of the film base.

Antihalation undercoating is a silver or dyed gelatin layer between the emulsion and the base, and is in fact a part of the emulsion.
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Re: Question for the darkroom guys. Re: Remjet

Postby Actor » Sun Aug 16, 2009 12:17 am

So what is the purpose of each? I know the anti-halation layer prevents halos around objects in the image by inhibiting reflection from the support, but what is the purpose of remjet, and why is it only found on movie film (or is it)?
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Re: Question for the darkroom guys. Re: Remjet

Postby richard p. t. » Sun Aug 16, 2009 1:51 am

Rem-Jet is, first and foremost but not exclusively, a type of anti-halation coating. MP film uses Rem-Jet for anti-halation because it offers other benefits for MP film - it has an anti-static and a lubricating function which is beneficial for MP film which is intended to be always 'on the move' in the camera (unlike still film). Differt films for different applications use different methods for anit-halation. BW neg has a neutral grey base. Some BW reversal films (Foma in particular comes to mind) uses an opaque silver layer under the emulsion which is bleached off in the reversal process. Colour neg still film and colour reversal MP and still films use a dye layer wich is under the emulsion and which is disolved out in processing.

Here is some info from a kodak page on film structure:

Three antihalation methods are commonly used:
• Remjet, a removable jet black layer, is the coating of carbon black particles in a water-soluble binder on the bottom of the film. It has four purposes: antihalation, antistatic, lubrication, and scratch protection. The remjet carbon layer is also conductive and prevents the build-up and discharge of static charges that can fog film. This is especially important in low relative humidity environments. Remjet also has lubricating properties. Like the supercoat on top of the emulsion, remjet resists scratching on the base side and helps transport the film through cameras, scanners, and printers.
Because remjet is black, it must be removed before the image can be seen. Remjet is removed during the first stage of processing, before the developer.
• Antihalation undercoating, a silver or dyed gelatin layer directly beneath the emulsion, is used on some thin emulsion films. Any color in this layer is removed during processing. This type of layer is particularly eEective in preventing halation for high resolution emulsions. An antistatic and/or anticurl layer may be coated on the back of the film base when this type of antihalation layer is used.
• Dyed film base serves to reduce halation and prevent light piping. Film base, especially polyester, can transmit or pipe light that strikes the edge of the film and result in fog. A neutral-density dye is incorporated in some film bases to mitigate this eEect. Dye density may vary from a barely detectable level to approximately 0.2. Higher levels are primarily used for halation protection in black-and-white negative films on cellulose bases. Unlike fog, the gray dye doesn’t reduce the density range of an image; it adds the same density to all areas just as a neutral-density filter would. It has, therefore, a negligible eEect on picture quality.

http://motion.kodak.com/motion/uploaded ... -image.pdf
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Re: Question for the darkroom guys. Re: Remjet

Postby Actor » Sun Aug 16, 2009 7:05 pm

Thanks everyone for all the information.

I've found a site with the procedure for processing Fomapan R, but it appears to apply to their 35mm slide film. Not being movie film it presumably does not have the rem-jet. To use the same procedure for movie film you would need an extra step to remove the rem-jet?

I'm very interested in trying to process Kodak Reg8 B&W film as a negative. (Because Kodak does not offer a Reg8 or Super8 B&W negative film.) I've been assuming that the classical process of develop, stop, fix, wash would work, but apparently I need to add a step somewhere along the line to remove the rem-jet.

By the way, how did the term rem-jet come to be? (Not really important.)
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Re: Question for the darkroom guys. Re: Remjet

Postby aj » Sun Aug 16, 2009 7:09 pm

The original foma reversal kit dissolves the backing. All turns out nicely. :)

Just use the chemistry one time only. The bleach oxidizes quickly and after one use it is full with gritty stuff which sticks to the second film, if tried. :(
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Re: Question for the darkroom guys. Re: Remjet

Postby richard p. t. » Mon Aug 17, 2009 2:23 am

Foma slide film (R100) is the same film as the cine film R100 they make. It is processed the same way using the same chemistry and proceedure as the slide film. It can also be processed in D19 developer, however it MUST be the very first use of that developer.
Because Foma R100 has a silver anti-halation layer, it cannot be processed as a negative, only as reversal.
Kodak's black and white reversal films do not have a silver anti-halation layer and so can be processed as either reversal or as negative (the latter using the simple dev, stop, fix proceedure you are familiar with). This includes the Cine-X standard 8 film you can buy (which is Kodak 7265 Plus-X). For anti-halation purposes Kodak bw reversal film uses a grey base instead of a clear base.
'Rem-jet' which is currently used only on colour neg MP film is a 'removable jet black' coating.

As for working with rem-jet stocks and hand processing using spiral equipment, it is possible. If one uses a borax pre-bath, some of the rem-jet is removed in processing. When processing is finished, the rest can be removed from the film with a cloth. This doess work but can be a very messy proceedure and the spirals also get quite dirty and need cleaning. This is not the way to do it in my opinion.

If processing ecnII (colour neg MP film) or old reversal colour films that have a rem-jet backing I advise using the proper ecnII pre-bath. This is very cheap from Kodak even though it comes as a 20litre box of concentrate. I pre-bath the film for about 30 seconds with adgitation and at a moderately high temp of 30 to 35 degrees. Then I extensively wash the film with adgitation. Generally this involves about 3 minutes of washing, emptying the tank completely once or twice until I am satisfied that the wash water is comming out clear. Then continue with the rest of the processing proceedure. At the end of processing, I have been imersing the spiral in more, clean pre-bath then spraying the spiral with presurised warm water to remove any last bits. This step may not be necessary, but I do it. It also pays to give the back of the film a cursory wipe with a cloth damp with final rinse when it is on your drying rack. The spirals come out completely free of rem-jet with this proceedure and there are no messy cloths or anything. This is of course, NOT how Kodak intends rem-jet to be removed. Kodak for instance specify a very short time in the pre-bath so that the rem-jet backing does not commence comming off in the bath. Rather a Kodak technician here told me the intention is for rem-jet to only come off in under the rem-jet removing sprays that are the next step in the conventional machine process - and there to come off in flakes rather than as a fine powder. If rem-jet flakes get on the emulsion, they can stick and create 'sparkle' in the image. This is why they don't want the rem-jet to start comming off in the pre-bath tank. However in my method which works for spiral reel processing the rem-jet is given time to thoroughly dissolve in the pre-bath to the point where I find this adhesion problem and sparkle are no longer a problem. Yes, the pre-bath ends up very dirty, but it is cheap and non-toxic.
cheers,
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