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Ian Grant
08-24-2007, 07:16 AM
Emulsion for High-Speed Papers

This gives high speed & high contrast.

Part A Mix at 0C


37.5gms Gelatin
75ml Water


Part B Mix at 20C

5gms Gelatin
18gms KBr
0.4gms KI
100ml Water

Part C In the Dark Room

18.3gms AgNO3
210ml Water


Warm to 70C mix Part C into Part B rapidly maintain at 70C for 2 minutes then add part A and ripen for 5 minutes.

Cool and set at 2-7C for approx 4 hours. Shred and wash at 2-7C. After ripen at 70 C for 50-60 minutes, with the addition of 2ml 1% KBr


This formula is ideal for document copying papers. I've posted it as this is one extreme of the emulsions suitable for paper coating.

Ian

ben-s
08-24-2007, 08:34 AM
Thanks for posting this Ian, it looks interesting.
Just a couple of questions;
Is the following a typo? - Mix at 0C seems rather cold



Part B Mix at 0C

5gms Gelatin
18gms KBr
0.4gms KI
100ml Water


And what kind of Gelatin is it using?

Ian Grant
08-24-2007, 09:02 AM
Ben, the formula doesn't specify what gelatin to use, but the type of Gelatin can make a significant difference.

Part B temperature - at 0C the gelatin will swell rather than dissolve, this may have some effect on the final emulsion. It's not something I looked into.

Ian

Photo Engineer
08-24-2007, 10:46 AM
Mixing gelatin with water this cold was a common practice for making the final swollen gelatin which was to be added later to the emulsion, but was not common for the 'kettle' gelatin as it had to be in a melted state in order to help form the crystals of silver halide.

I would guess that this might be a typo myself, but not having run the formula IDK. I will say that 18% KBr at 0 C will be hard to dissolve, in fact almost impossible. This gives me an additional hint that there is an error here.

OTOH, maybe the formula relies on having these things be solid crystals and cold during precipitation. Just because I have never seen such a formula before, I don't want to rule it out.

Ian, have you made this emulsion as it is printed above?

PE

Ian Grant
08-24-2007, 11:28 AM
Ron & Ben, in re-writing all the emulsion formulae I investigated I've been making the Parts A,B & C consistent, A main Gelatin, B halide solution, C Silver solution inadvertently applied the wrong temperatures.

So I've corrected the initial Formula posted here. Part A should be mixed at 0C, Part B at 20C as Ron would expect.

Ron I didn't make this exact formula but compared it to one of my trials batches and made adjustments to improve speed and contrast.

Ian

Photo Engineer
08-24-2007, 11:40 AM
Ian;

Thanks. That clears things up with me.

PE

ben-s
08-24-2007, 11:58 AM
Ditto. makes much more sense now :)

Ron; what do you reckon - active or oxidised gelatin?
I'm guessing active?

Ian Grant
08-24-2007, 12:04 PM
Ben this is an older formula, probably pre WWII, so it's unlikely it was for de-activated Gelatin.

Ian

Photo Engineer
08-24-2007, 12:04 PM
I cannot tell from the formula.

You see, addition rate can control contrast and speed, and temperature can control speed. I have not made this one, and in fact none that I have made at home are higher than 65 C, so that extra 5 degrees can make a difference.

Who can say unless it is made and tested and even then, the batch of gelatin makes a lot of difference even if it is the 'correct' kind for the make.

My enlarging speed emulsion is roughly similar but uses a sulfur finish and oxidized gelatin and a lower temperature as well as a very slow addition rate. It also uses rhodium chloride. So you see that there is a lot of variation in possible formulas and outcomes.

Double run emulsions are much easier to predict. At least to me they are.

PE