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Photo Engineer
06-24-2010, 02:41 PM
Ray;

At 0.1 g/l, the value given above, I assure you that the vAg is positive. In a plot, this does not show up well though and for the most part work is carried out in the negative range for NaBr. For NaCl though, most all values are positive, and for KI they are not positive at all IIRC.

PE

Ray Rogers
06-24-2010, 04:11 PM
Ray;

At 0.1 g/l, the value given above, I assure you that the vAg is positive. In a plot, this does not show up well though....

PE
Thanks for the clarification....

Kirk Keyes
06-24-2010, 05:29 PM
I think by converting the Molar concs of the x-axis into log(mole conc) will give a pretty straight plot for the curves and you can also see that the lines go into positive values as the concs get lower than 1 Molar.

Photo Engineer
06-24-2010, 06:07 PM
I think by converting the Molar concs of the x-axis into log(mole conc) will give a pretty straight plot for the curves and you can also see that the lines go into positive values as the concs get lower than 1 Molar.

Oh, I agree, but then someone would say "why are you using logs, why not 'real numbers'?" :D

You cannot please everyone at the same time but you can anger or annoy everyone at the same time.

PE

Kirk Keyes
06-24-2010, 06:15 PM
I think PT Barnum said that once.
;^)

Photo Engineer
06-24-2010, 07:49 PM
I think PT Barnum said that once.
;^)

He said "You can please some of the people some of the time but not all of the people all of the time!"

Or maybe it was someone else. IDK. I am unsure because I don't want to displease anyone.

PE

Ray Rogers
06-24-2010, 08:11 PM
Kirk, to do that would involve extrapolation, correct?

Which method of extrapolation would you consider suitable for this data?

Similar data I have seen before has always been on logarithmic graph paper... and covered the full range of interest; if you find your Excell sheet perhaps it can be fleshed out a bit without the need for extrapolation....

A similar version:
You may fool all the people some of the time,
you can even fool some of the people all of the
time, but you cannot fool all of the people all the time.

Photo Engineer
06-24-2010, 08:45 PM
Ray;

This mV chart is limited by the pAg scale and by the PKSPs of the halides. Therefore it asymptotically approaches a limit at each end. The low limit is AgI at about -300 or more mv and the upper limit is AgCl at about +250 mv. Mixes are in between. A log scale would be linear in shape but not in concentration as is obvious and may confuse some people. A non-log scale is not linear as shown in my example above.

Extrapolation is not necessary as the curve I showed is entirely calculated and is therefore an extrapolation itself requiring only more data and "running time" to extend the curve. But, this serves no purpose in most cases as 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. This comes from the basic properties of Silver Halides.

The same can be said for the final pH of an emulsion BTW. However, in this case it controls speed and contrast instead of fog and keeping.

PE

Ray Rogers
06-24-2010, 10:31 PM
... about 0.1 g/l of NaBr or a vAg of about
-50 to -70 mv at 40 deg C

cf


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


???

It looks like the VAg in both quotes (both 0.1 g/l) have different signs...

hrst
06-25-2010, 03:59 AM
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!

Kirk Keyes
06-25-2010, 07:53 AM
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.

Photo Engineer
06-25-2010, 10:29 AM
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

Ray Rogers
06-25-2010, 01:04 PM
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" ?

Photo Engineer
06-25-2010, 03:51 PM
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

dwross
06-26-2010, 08:31 AM
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

hrst
06-26-2010, 09:44 AM
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 (http://www.tkt.cs.tut.fi/index-english.html); and my friend is a student of material science (http://www.tut.fi/index.cfm?mainsel=13718&sel=13718&Show=18874&siteid=150&CFID=169700441&CFTOKEN=49169555), 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 :D. 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 (http://www.students.tut.fi/~alhonena/kandi_v099.pdf) (pdf is in Finnish but has an English abstract) I'm building but it seems that lab will take some more years to complete :p

We/I do the emulsion work at our university's photography club (http://www.students.tut.fi/~kamerat/en/)'s darkroom which is small but I like the atmosphere.

dyetransfer
06-26-2010, 12:39 PM
[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

dwross
06-27-2010, 10:20 AM
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 :D.

'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.

alexhill
06-27-2010, 08:45 PM
Awesome results! thank you so much for sharing them with us. You set quite an high benchmark for film quality.

keithwms
06-27-2010, 08:56 PM
Very nice to read about this progress.