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1. Originally Posted by Ray Rogers
cf

???

It looks like the VAg in both quotes (both 0.1 g/l) have different signs...
I think the first is in reference to bromide and the second is chloride.

2. Ray;

In post #29, which does not reproduce well if quoted, I think you have combined 2 different passages and mixed information. Can you give the post numbers that you used of mine so that I can give the correct or clarified figures?

PE

3. The flow of logic went as follows:
(#1)
#6 === #21 (positive VAg)
#28 (Negatve VAg)
-------------------------------------------
HRST makes a statement about a particular halide conc. in his inital post (#1)
You comment in #6 about positive VAg
and defend this comment in post #21
but switch signs in your post #28 when you mention Negative VAg
-------------------------------------------
(#1)
We used a simple conductivity meter to measure wash water compared to conductivity readings of NaBr solution of 0.030 g/l, and found out that the washing step was quite quick, less than one hour. For final wash, we used NaBr at 0.100 g/l in wash water.

#6
At that concentration of NaBr after the wash,
[this presumably can only refer to the 0.100 g/l NaBr in post #1]
at 10 deg C (a good wash temp), the vAg would be about +37 and at 40 deg C (a good coating temp) it would be about +67 mv. This is a very good position for the final emulsion.
I often aim for about +50 mv.

#21
At 0.1 g/l, the value given above, I assure you that the vAg is positive.

#28
we only need to know that about 0.1 g/l of NaBr or a vAg of about -50 to -70 mv at 40 deg C is optimum for keeping and fog prevention.

==================================================
To simplify:

Why if "a vAg of about -50 to -70 mv at 40 deg C is optimum for keeping and fog prevention would you "often aim for about +50 mv" ?

4. Ray, everyone;

My post #28 has a typo in it. The correct final vAg for a washed emulsion should be about +50 to +70 mv at 40 deg C. If you go much higher, the emulsion can fog. This assumes a Bromide emulsion. The value is correspondingly higher for a Chloride and lower for an Iodide.

Sorry for the error. Thanks Ray for a good catch.

PE

5. Originally Posted by hrst
Update:I managed to build a prototype of a 35mm perforator. It wasn't impossible at all, in fact I'm surprised I made it in one night (that was an all-nighter, though). Perforations look quite awful, but IT WORKS, and I believe it's usable because the requirements are not so high in still photography. Perforating two holes at a time is tedious so I started to automate it. I made six large electromagnets that hopefully will be strong enough to punch the holes. I'll post more details later!
And the fun, exciting news just keeps coming from y'all! Needless to say, I hope you publish all the details. And not just here. APUG's great, of course, but I think recent conversations show that it shouldn't be the only place information gets placed. As PE pointed out -- it can get GWTW (which I had to google: Gone With the Wind). I tell myself that silver gelatin emulsion research isn't Peace, Equal Rights, or Not-Oil Energy, but it's still important. (Ron, it's really time for you to get something on paper and/or your own website for posterity.)

hrst, I'd love to know more about you. You say 'we' sometimes. Are you part of a team? A student? Is this research part of your graduate work? I have my fingers crossed that it is. You could be at the forefront of some really significant contributions. Anonymity is fine, of course, and for better and for worse, is part of the internet culture (I tried to stay 'gender neutral' until PE outed me) but it would be fun to put some of your great ideas in a personal context.

Denise
www.thelightfarm.com

6. Denise,

I think I could publish the drawings & instructions of a simple perforator for The Light Farm, if it is fine with you! I agree that APUG is a good medium for discussion and blog-like newsflashes, but you're right that a web page is better for "completed" information.

Occasionally I say "we" and occasionally "I". This is because I have a friend who I'm making emulsions with, but he seems to be quite busy (with work and his family) so when he's not available, I make things alone. I live alone so it's easier! I am a BSc, a student of computer science; and my friend is a student of material science, thus having access to some of the labs etc. Both of us work on part-time (and full-time at summer) as research assistants on our corresponding departments. Mainly we have taken advantage of de-ionized water, magnetic hotplate stirrer with temperature feedback control and now the corona treatment unit. My objective, however, is to become independent someday so that I can make this all at home.

This emulsion work is "just for fun" for both of us. I'm afraid it's not that easy to do MSc thesis on emulsion making to the department of computer systems . Although there would be possibilities for computer automation, but I already have a subject for my MSc that relates to my (paid) work at the department, design of the integrated circuits. My BSc thesis was about the Motion Picture laboratory (pdf is in Finnish but has an English abstract) I'm building but it seems that lab will take some more years to complete

We/I do the emulsion work at our university's photography club's darkroom which is small but I like the atmosphere.

7. [QUOTE=hrst;1017537]We used pig skin food grade gelatin and home-made silver nitrate again and used a modified version of PE's "A real formula" topic. We did the addition of silver in a similar way that is described at Jim Browning's website, but speeded up a bit.

Contrast is quite high. Maybe we should use the exact silver addition numbers in Jim Browning's document. Now we speeded it up by about 20%. This emulsion might be best shot at EI 16 and developed for only 4 minutes or so, with less agitation.

Congratulations on your great work! I'm particularly interested in your use of corona discharge. This would be important in the production of matrix film, as Dupont doesn't stock the only polyester film base product that works for Dye Transfer - all other subbing layers I've tested pickup dye and stain the print. So, if the corona discharge method works well, that would be a great option. If you can determine the proper methods / voltages, etc, I would be very interested.

As far as the addition methodology I used for making a matrix film, I don't know how it would work for an optical negative film for enlarger use. I designed the emulsion by trial and error, and the iodine addition, silver nitrate addition and even the yellow dye addition all were used to control the tone curve. I didn't monitor the tone curve of the silver image, it was done by rolling a print and working to get a straight line on the print. The result is exceptionally straight tone curve with a short toe - in fact superior to the old Kodak matrix film. I don't know how this would translate to the curve on a taking film, but it looks like your results are very good.

Regards - Jim Browning, Digital Mask

8. Originally Posted by hrst
This emulsion work is "just for fun" for both of us. I'm afraid it's not that easy to do MSc thesis on emulsion making to the department of computer systems .
'In the pioneer days, photographers had to make their own emulsions, and it was by the combined efforts of a small coterie of experimenters at the end of last century that the modern "dry plate" came into being. Some of these men were pure amateurs, others were practical chemists and men of scientific training. Out of this little band of experimenters came the founders of most of the original commercial emulsion-coating factories.' (T. Thorne Baker, Photographic Emulsion Technique, 1941, p.x).

I will be delighted to publish any and all of your 'just for fun' on TLF. Thank you very much for sharing your background. It sounds like you and your friend are in a great place for photographic exploration.

9. Awesome results! thank you so much for sharing them with us. You set quite an high benchmark for film quality.