Developer replenishment for double-sided xray film

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BetterSense

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I use replenished developer, and I'm supposed to add 23mL of replenisher for every 80sq inches of film developed.

Xray film has emulsion on both sides of the film, so at first I thought I should replenish 46mL for every 8x10 sheet. However, because of the dual emulsion, it develops to usable contrast very fast. So maybe since I'm developing to a contrast index similar to normal film, what I really have is 2 sides, each half-developed, and therefore I should replenish normally.

I'm not sure what process it is exactly that leads to the need for replenishment. I assume the only parameter that matters is how much silver is reduced. So since I'm developing to the same contrast, should I replenish normally or double?
 

Lowell Huff

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replenishment rate for xray film

You don't say what type of developer you are using, MQ or PQ. It is easy to over replenish with MQ developers and then you lack consistancy of image: PQ developers allow uniform control. With PQ type developers, as the density gradually falls, add working strength to the system and that will maintain activity. We recommend a replenishment rate of 50 mls per sq ft, 75% exposed.
 

Lowell Huff

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replenishment rate for xray film

You do not indicate whether you are using a MQ or a PQ developer. MQ types are very difficult to control and can make the developer too active. PQ developers are easily replenished without creating an over active developer. We recommend 50 mls per sq ft, 75% exposed.
 
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BetterSense

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Well, in the absence of any advice on the matter i've been replenishing normally, even though the film has two emulsions.

It's my theory that when developed to a printable contrast, the amount of silver reduced by the developer should be the same with single-or double-sided film...the same amount of metallic silver, just spread between the two sides of the film. I figure fixer life is cut in half, though.
 

AgX

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Replenishment rates only apply for a `mean exposure´ (whatever that be...) and for a given type of film material.
 
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BetterSense

BetterSense

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If you have double the square inches of emulsion (double sided film) then you need to replenish x2.

Why? What if there are double the square inches of emulsion, but the average amount of reduced silver is half as much per area? If you developed a bunch of film and it came out clear because you left your lens cap on, should you replenish at all?
 

AgX

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Developer replenishment aims mainly at the redox-reaction.
(In case there is none you would have to employ bath volume compensation where appropriate.)
 
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BetterSense

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Developer replenishment aims mainly at the redox-reaction.

So it would be proportional to the amount of silver reduced from silver halide to silver metal, correct? Is there any tests you can do to see if your developer is being over-replenished or under-replenished? Something simple like pH?

Right now I add 23mL of DK25R to my D23 for every roll developed, until I have added half of the original D23 solution volume in replenisher, then I start over with a new batch.
 

AgX

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I would like to have some physico-chemical test. But why do process-chemistry manufacturers all advise on sensitometric tests when using replenished processes?
 
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I suppose I could shoot a roll of 35mm full of zone-1 exposures, so that I could at least verify that I am not losing speed as replenishment goes on.

I believe D23 can be replenished until an equal amount of replenisher has been added, but I only replenish until 1/2 the amount of replenisher has been added. Probably this safety factor helps keep things in spec. I have made several batches of D23 and replenished them till the end with no problems; I have only started worrying about over- or under-replenishment when I started shooting lots of xray film.
 

Anscojohn

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Pardon my baleful ignorance, but why is x-ray film coated on both sides?
Also, it seems to me your replenishment regime for D23 with DK25R is eminently sensible.
 

AgX

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X-ray photons are much less absorbed by silver-halides than are light photons. To gain speed medical X-ray films should have more halide. For coating and developing issues that amount is divided between two opposite layers.
However with the introdution of the fluorescent foils the share of X-rays on exposure is greatly reduced.
Furthermore is that concept of double-coating abandonned for some film types to gain sharpness.
 

Anscojohn

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X-ray photons are much less absorbed by silver-halides than are light photons. To gain speed medical X-ray films should have more halide. For coating and developing issues that amount is divided between two opposite layers.
However with the introdution of the fluorescent foils the share of X-rays on exposure is greatly reduced.
Furthermore is that concept of double-coating abandonned for some film types to gain sharpness.

*******
I see.
 
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