Making my first emulsion now.

[Photo Engineer]

Once formed by overwashing, over ripening, over digestion or over finishing, fog is difficult to remove. In the case of overwashing fog is caused by the high vAg which produces or allows production of more Silver metal which can act as a fog site. The KBr must be added at the time of washing when the endpoint is reached. The others produce fog by forming more Silver sites on grains through too much of a good thing!

Ideally to stay between +100 and +50 mv you will need about 0.029 and 0.192 g/liter of NaBr at 40 deg C.

To retard all fog, try using Tetra Aza Indene, sold by the Photographers Formulary either as powder or pre-prepared solution.

PE

 

[hrst]

Safelight!

Oh, the fog was (at least mostly) safelight fog! It seems that erythrosine gives quite good sensitization even to yellow wavelengths.

Our orangish-red LED safelight won't fog any multicontrast enlarging paper at all, but 1 minute from 15 cm distance gives almost dmax on our emulsion -- that corresponds to about one hour at 100 cm in black room. We used the same safelight in the first, non-erythrosine emulsion.

We used the safelight all the time. Now we know what to do: go towards longer wavelengths (625 nm), reduce safelight level as much as possible and use it only when necessary.

It's very reassuring to note that the wash is probably not the main culprit, or a culprit at all, and that the spectral sensitization really worked quite well.

 

[dwross]

Congratulations on the great detective work and your ever-improving emulsions! It's a lot of fun to hear about the progress of your work. Thanks for sharing.
d

 

[filmfabrik]

hrst,

i am fascinated of your results, too - thank you very much for sharing them!
You said, that you would like to try some extracted chlorophyll as red sensitizer - (how) did it work?

best regards,

Peter

 

[hrst]

filmfabrik,

We have not tried chlorophyll yet. I have it extracted but we'll first try to make a proper ortochromatic emulsion with little fog and more speed. Then it's time to try chlorophyll...

Currently we are working to make electron bombardment machinery to "sub" PET. I just made a working high voltage source using flyback transformer but I got barely 5 kV, it's not probably enough. Voltages to 20 kV should be easily possible so I have to redesign it a little. But, this is not so complicated (nor dangerous) as it may sound.

PE, do you happen to have some specific information about acceleration voltages needed for PET electron bombardment ?

 

[Photo Engineer]

Yes, it is basically the electrostatic charging method used in Xerography. A charged wire over the film with a grounding plate underneath. The film passes between the two while a corona discharge takes place through the film. The top surface facing the discharge wire is then given a tooth that allows hydrophylic coating.

This charge, if done properly, will last about 24 hours or less. I've coated within 24 hours of the charge and also in-line. Just remember that the corona discharge may appear faint, even in the dark, but is high in UV and will fog film and paper.

PE

 

[hrst]

Thank you so much for this information! My idea was to use hot cathode (halogen bulb) to emit electrons and accelerate them using electric field, but what you describe is indeed just like in copier, which is quite simple. So I'll abandon the hot cathode idea, this is easier. Thanks!