My recipe is "Osterman’s 1880 Gelatin Bromide Emulsion", I found it on http://thelightfarm.com/Map/DryPlate/Osterman/DryPlatePart4.htm. I coat the plates with a syringe，6ml emulsion per 4x5 inch at 40-45℃.Pour it on the plate and spread it out with my fingers.Can you provide details on your recipe and how you coat your plates? That information would help troubleshoot. I have seen similar artifacts in my coatings .. this is the first time I've seen it from someone else other than once on a very old plate.
Thank you for your reply：），it appeared on my all plates， it's a disaster for me, I'll try my best to solve the problem。The couple of times I've seen this on my own plates, I attributed it to incomplete incorporation of the finals. Longer and more careful stirring seemed to fix things. (Not more vigorous. That might incorporate bubbles into your emulsion.) However, I have no doubt there could be other causes. Good luck with the detective work.
Thank you for your reply ,Do you use a surfactant or do you use alcohol as Mark does? Did you use Distilled Water or tap water for the wash? What did you use to clean the plates?
PE
A long ripening time may be the point, I always put the emulsion in waterbath(45℃) for a longtime while I coating the plates；and the second ripening I mean after wash the gelatin, I ripen it for 30' at 50℃. Based on your theory，it's a problem. Thank you for your reply, I'll make some new emulsion.I think it was due to long first ripening due to long cooldown time. Scaling to a larger batch without adjusting for the longer temperature cooldown cooked the halides longer during first ripening. It was pretty bad...perhaps the gelatin breaking down too much? When I adjusted for that (cooling down at same rate as my smaller batches) the effect went away but sometimes I see it..which makes me think that my cooldown is still a bit long. I’ve been reducing the cooldown time incrementally from batch to batch (chiller actively cooling the water bath) to chase this theory down while also watching for effect on emulsion speed. Right now my precip time is 12 minutes, then 13 minute hold at 55C, then 30 minute cooldown to 40C. I then dump add gelatin and melt it over another 10 minutes and then pour into large tray and in the fridge as a thin layer to set.
My other theory is that it’s on the coating side, either from the jar of emulsion sitting at 104F without stirring as I work through the coating session, or pressure sensitizing parts of the emulsion when I squirt it through the syringe. I’ve been adjusting my technique which helps, but however I adjust my technique it has to stay efficient because of how many I have to coat.
Long heat time may be the point I think, I always put the emulsion in waterbath for over 1 hour......My suggestion...
Do not use any mechanical means to spread the emulsion. Let is spread naturally without rods, fingers and etc. Flow might do the job.
Long heat times might denature the gelatin and cause problems
PE
I weared gloveswere your fingers ( that you spread the emulsion with ) clean ?
Because the stripes contaminate the picture after develop.What did you decide was the problem?
The pressure will be a problem? The silver nitrate is AR, the best I can buy in my country, cooling time...I didn't notice,after first ripening ,I bring the emulsion into fridge immediately.Interesting. I use a similar method (syringe, 5ml for 4x5) except I use a clean glass rod instead of my fingers to spread the emulsion.
Ron, I know the sensitivity of silver halide can change if subjected to pressure. Do you think the sensitivity could be altered if yhe emulsion is pushed forcefully through the syringe?
Other questions: Subbing layer? What is the source / purity of your silver nitrate? What is your cooling time like after precipitation and first ripening?
Leave out the chrome alum and thymol. Neither are necessary and may be the cause of your problems. That leaves only alcohol in the finals. It should be much easier to evenly incorporate it. When it comes time to process your plates, keep the chemistry on the cool side and handle the plates reasonably gently. Also, you don't need to use a syringe. Use a round-bowled plastic measuring spoon. After you've poured the emulsion on a plate, you can use the bottom of the spoon to spread the emulsion. Coating goes very quickly this way. You minimize the chances you'll add bubbles to the plate and you greatly reduce the chance of introducing contaminants. Big Bonus: As simple and inexpensive as you could ask for.
Thank you for your advice. I will try.
Thank you sir I‘ll tryIt is best to coat at about 40 deg C. You should preheat the plates. If you do not have a doctor blade, you should spread the emulsion by pouring in the center and then tilting to spread the emulsion. See attached.
Photos courtesy Mark Osterman of GEM.
PE
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