Ortho sensitve emulsions

[Photo Engineer]

There has been some discussion herabouts regarding the senstivity of films and papers. So, having access to a spectrosensitometer, I have put together a small demo for you all.

First off, a spectrosensitometer is a special sensitometer that uses a monochromator (that is a device like a prism that splits light up into its components) and presisely exposes film at equal energy in 10 nm (nanometer) increments from 400 - 700 nm, which is the visible spectrum.

The examples that I show are as follows:

1. Raw emulsion (AgBr)

2. Sensitized emulsion (I overdid it a bit so it is foggy)

3. 1x level of ortho (green) spectral sensitzing dye added to #2.

4. 2x level

5. 4x level

6. Ilford MGIV paper

Now, the dye I used is a little long, I would prefer something that does not go so far into the red region, and the dye isn't perfect for ortho sensitivity either, but this is a first approximation of an ortho sensitive material.

Anyhow, this is the type of test used to view the sensitivity of a film or paper. These coatings were on Strathmore Smooth at 500 mg/ft square of silver and 1000 mg/ft square of gelatin. Glyoxal was the hardener, TX100 was the spreading agent, and the process was Dektol, stop, hardener fix and wash.

This not only shows where the silver-gelatin experiments are, it gives you a benchmark for what can be achieved with silver-gelatin. This paper material has an in-camera speed of ISO 25 which is what the Ilford MGIV has under identical conditions.

So, if you cut up some MGIV and expose it in-camera, you have a mighty fine ortho paper negative material, however, the contrast varies as a function of color which is a bit odd when you see the results.

PE

 

[Michel Hardy-Vallée]

PE you are ef-fing AWESOME!

Care to repeat the test with graded paper?

 

[Ryuji]

This paper material has an in-camera speed of ISO 25 which is what the Ilford MGIV has under identical conditions.

I disagree. Ilford MG4 has very much lower than that speed, more like 2.5 or lower, if you measure it as a negative emulsion. Of course, one of the problems is to develop the emulsion to a g-bar of 0.62 but even if you accept 2 or so, the speed is still very low.

But bromide emulsion should be easily capable of 25 speed.

In particular, your raw and digested emulsions look quite a bit lower contrast compared to MG4 with monochromatic green light, so it should help you in getting speed above 25.

Also, I don't know which dye you used (it doesn't show J-aggregate so it's not the ones used for color films), but it doesn't exhibit much desensitization with extra dye, so I suspect you added quite a bit of iodide, or made it core-shell?

Finally, do you have a color scan of the test prints?

 

[Photo Engineer]

I disagree. Ilford MG4 has very much lower than that speed, more like 2.5 or lower, if you measure it as a negative emulsion. Of course, one of the problem is to develop the emulsion to a g-bar of 0.62 but even if you accept 2 or so, the speed is still very low.

My exposure was using a piece of MGIV cut to fit a Polaroid holder, then placed on the back of my Mamiya RZ67. The meter on the polaroid back was set at 25, and I used a hand held Sekonic spot meter to verify the exposure. My own emulsion was exposed in-camera using the same method. So, I have in-camera comparison exposures.

All exposures were then processed and gave good images of the subject material which was a MacBeth color checker.

The experiment also included Polaroid film, Endura color paper and several other B&W papers. I have only included a small fraction of the data here.

PE

 

[Ryuji]

Ron, that's not how ASA (or ISO) film speed is measured. We measure speed by the toe exposure at a fixed g-bar, you know that.

But if you are getting speed comparable to MG4, that'll tell me something about the speed of your emulsion.

 

[Photo Engineer]

Ryuji, I know how to measure ISO, EI and ASA speeds as well as several other methods you may never have heard of.

I have posted some valid results and have ISO 25 pictures to back up the results. I also have comparisons from Polaroid exposures. In addition, the wedge spectrograms were done with a fellow engineer present and were verified by him. These exposures were done a few months ago, and were only posted after I had accumulated all of the various pieces of comparison data.

If you have objections in the form of concrete data, you are free post your actual results. Pictures, wedge spectrograms or step wedge exposures would be appreciated. My pictures with step wedges are posted elsewhere.

I wish you the best.

PE

 

[Ryuji]

Ron, Im merely pointing out that Ilford MG4 has ISO film speed of far below 25 even if you accept g-bar of 2 instead of 0.62. The actual speed I get is one-tenth of that. That's all I'm saying. You say you have valid results, but anyone can confirm my claim by sticking in a piece of MG4 in their camera to expose it as if ISO 25 and get a very thin image.

I understand that your wedge spectrograms were properly obtained. I could estimate the speed increase from your digestion process (actually, the toe speed didn't seem to increase much, probably due to the fog, and lack of gold) from them, for example. I also see that your emulsion is far softer than MG4 to monochromatic green light, but still far harder than negative emulsions. I'm actually pretty familiar with wedge spectrogram.

I have data for test emulsions, but I'm way past the stage where I get excited every time I get something new. I use triple jet precipitation (one of them is high linear velocity mixer for controlled iodide injection) I can control key parameters independently, and I usually get effects predicted by existing knowledge and computer models of precipitation process.

 

[df cardwell]

Thanks PE

The MGIV info is a neat bit of information, and I can use it today !

( being just a humble picture taker, I appreciate it. )

 

[Mick Fagan]

Hmmm, very interesting piece of information.

Tomorrow I'm doing a film speed test of a new film I intend to use. But this posting has given me something else to do as well

I've just figured out a way to insert small pieces of MGIV to the back of my Nikon F3.

I'll do a few tests on a grey scale and colour chart as well as a pictorial print.

I don't assume a speed of 25 ISO will be great, but it shouldn't take much time to get a working ISO using your information as a start.

Nothing like a bit fiddling here and there to keep the grey matter ticking over, eh?

Many thanks, Mick.

 

[Photo Engineer]

The problem with evaluating speed in MGIV or any MC paper is multifold.

1. Which emulsion do you check for speed point? There are at least 2 in MGIV.

2. Since there are two contrasts, which emulsion do you develop to the ISO standard?

3. Since it a paper, how do you apply film rules.

4. If you develop to a gamma of 0.62, this is severe underdevelopment of a paper material therefore leading to low threshold speed estimation.

So, the practical problem as opposed to theoretical problem is "what do you do to use a paper as an in-camera negative material".

I chose to meter it as if it were a negative material, and therefore got an effective ISO which is in reality an EI of 25 for MGIV. So, if you take MGIV and put it in your camera you can expose it at EI 25 (ISO 25). It works. The pictures are not perfect, but they indicate that the ISO (EI) is close to 25. Endura paper, BTW, is about 25 also when filtered to daylight. I knew this for almost 30 years, having used it (type "C" paper then) many years ago, but the contrast is again high.

There is the balance between theoretical and practical knowledge. Theoretically, developed to a gamma of 0.62, MGIV is underdeveloped and has low speed, but deveoped to a gamma of 2.5 has a speed of about 25 and yields decent pictures in-camera when the negative is scanned and inverted. You can do this in the darkroom or using a digital scanner editor program. You may also wish to lower contrast by using a low contrast grade paper or by digital means. I have done both.

I have examples of most of this on-hand to post if desirable to members. I ask Ryuji to post some examples to further extend our knowledge of silver-gelatin. We have seen many of his comments, but practically none of his work. Seeing some of it would be most helpful to us all, I'm sure.

PE

 

[Photo Engineer]

Hmmm, very interesting piece of information.

Tomorrow I'm doing a film speed test of a new film I intend to use. But this posting has given me something else to do as well

I've just figured out a way to insert small pieces of MGIV to the back of my Nikon F3.

I'll do a few tests on a grey scale and colour chart as well as a pictorial print.

I don't assume a speed of 25 ISO will be great, but it shouldn't take much time to get a working ISO using your information as a start.

Nothing like a bit fiddling here and there to keep the grey matter ticking over, eh?

Many thanks, Mick.

Mick;

Please keep in touch. I am most interested in your results, particularly in view of the comments preceeding yours.

My development was in Dektol 1:3 for 1 - 3 mins by inspection.

PE

 

[Ryuji]

Ron, whatever story you like to create, but with EI 25 and developed in Dektol, how do you get 0.1 density above gross fog? You won't get that in daylight.

Your reference to gamma of 0.62 is incorrect. Gamma is the slope of the straight line portion of the curve, while ASA (and ISO) standard method for b&w negative films specify average gradient or g-bar. They are different quantities measured by different calculation on the sensitometric curve. On the other hand, speed measurement for print emulsion doesn't specify the contrast at all but calculate the speed by 10000 into the exposure (H) to yield the reflection density of 0.6.

Say an enlarging paper has ISO P500 speed, has short toe and reasonably straight line curve of g-bar of 2. This is typical of fast enlarging paper. That means we need H of 20 to get 0.6 density, and therefore H of 10 or a bit less to make barely discernible exposure above base and fog. Now, ISO b&w film speed can be estimated by dividing 0.8 by this exposure (H), which is around 0.1, even if we accept the g-bar of 2 instead of g-bar of 0.62. Most people expose paper negative at EI of 0.5 to 6 range, lower end of which is more common, because they are not necessarily exposing strictly for the shadow density, but because they consider the image is of sufficient quality if midtone and highlight are registered. So this accounts for the discrepancy between calculation and practice. However, a claim that the sufficient image quality can be obtained at EI25 is way off, based on both experience and calculation.

I have shared a lot of information about my emulsion as well as processing chemistry with many people on my web site and pure-silver. I have scans of my images made with my emulsion on the web as well. I've even given a free private emulsion-making workshop in Boston to several people.

In relation to sharing info with you, I've even told you how to desalt emulsions using phthalated gelatin precipitation method, how to manage fogging problems during optimal digestion problem, how to get maximum speed by making core-shell emulsions, etc. but I see you are having problems with the desalting and fog control, at least. I certainly won't bother to post every time I get some data.

 

[Photo Engineer]

Here is Ilford MG IV exposed at ISO 25.

The paper negative was scanned, reversed and inverted to give a proper positive image.

Included is the similar exposure with my ortho emulsion.

Please post your own examples before you continue your theoretical comments.

PE

 

[Photo Engineer]

Regarding ISO washing and desalting, I have been involed in that since 1965, it is merely a matter of getting commercially available PA gelatin. Nothing has been shared with me at all in any way whatsoever by anyone outside my circle of EK engineers. In fact, I have given the name of one of the sources of my PA gelatin out freely.

Nothing has been shared with me regarding spectral or chemical sensitization either. All that I have comes from EK or from EK fellow engineers. All that I share outside that circle is not proprietary.

PE

 

[Ryuji]

Regarding ISO washing and desalting, I have been involed in that since 1965, it is merely a matter of getting commercially available PA gelatin. Nothing has been shared with me at all in any way whatsoever by anyone outside my circle of EK engineers. In fact, I have given the name of one of the sources of my PA gelatin out freely.

Nothing has been shared with me regarding spectral or chemical sensitization either. All that I have comes from EK or from EK fellow engineers. All that I share outside that circle is not proprietary.

PE

What a complete nonsense. I have copies of all email correspondense I made in the past. I sent you an email describing how to make phthalated gelatin in 10 minutes, how to use it, and some of the tricks to make good solid curds. I also told you good options as to how you can double wash with minimal work. But it seems that you can't make good use of phthalated gelatin... too bad.

I also named a few of ortho dyes I have used with good results in Photo.net. In a different thread there, I also told you good antifoggants for both chloride and bromide emulsions. But your emulsions seem to have too high fog level... Oh well.

If you google enough, you'll also find an infrared dye I use.

Too much nonesense, this is exactly why I don't want to share any more info with you.

 

[Photo Engineer]

Ryuji;

My problem with ISO washing was obtaining a source of good phthalated gelatin, not with how to carry out an ISO wash. I don't have an organic chemistry lab to synthesize phthalated gelatin, nor does anyone else here I suspect, so I located a source for it. I gave you the name and telephone # of my source. My goal is to give those to the members of APUG so that they don't have to synthesize PA geltin. They are not organic chemists. As a result, your instructions are useless to the majority of the readers here.

I asked you for the source for your dyes and you didn't give it to me, just the names of the dyes. Again, useless to the readers here. Quite a difference between name and telephone # which I gave you. I will make the dyes that I use available to all users here when my tests are complete.

In addition, I gave you the ratio of sulfur / gold and levels for different grain sizes. You didn't know them. That also will be published by me. If you publish it, remember, you got if from me!

Now, all of this is diverting us from the main issue of results. Mine are posted above.

PE

 

[Ryuji]

Huh? This is insane, Ron. It's amazing how story changes over time.

I make all my phthalated gelatin myself and they are of very good quality. It takes 5-10 minutes of reaction time. I also make gelatin sheets in dry form after phthalation, which takes more work than phthalation itself.

I have my data for optimal digestion for different grains, but I don't have yours. But I'm not worried, my grains are core-shell tabular grains of at 3 layers and whatever you have is not applicable to mine. I create sulfur, gold and reduction sensitization centers at different parts of the grain, and my technique is not dissimilar from what's published in literature.

 

[DannL]

I'm really enjoying this thread and you guys are at the top of my list.

I'll tell you what . . . . I'll serve the martinis (shaken or stirred) if you two will let me sit and listen for awhile.

What ya think????

Anyone want olives??

 

[Ryuji]

No thanks, I'll have tons of Guiness later tonight.

 

[removed account4]

SNIP

I'll do a few tests on a grey scale and colour chart as well as a pictorial print.

I don't assume a speed of 25 ISO will be great, but it shouldn't take much time to get a working ISO using your information as a start.

Many thanks, Mick.

mick:

several years ago i compiled a list of (15?) papers and their relative asa's, it was pretty easy, i made 4x5 sheets, stuck them in my speed graphic and made test exposures. i also called kodak and asked them what the asa's were for the few papers of theirs i had in my stockpile ... ( i figured i would compare notes ). i mentioned why i was calling, and asa's i had come up with. they gave me high speeds for their papers, and they made no sense to me. when i mentioned that i had asa 6 instead of 25 i was told film speed and paper speed are measured differently - and then i was told my (film)asa 6 was like their (paper) asa 25 ...

maybe they only use blue light, and i use daylight or a (xenon) strobe?

i don't know ... i know that regular old photo paper ( i am using polymax mgfb, kodak mgfb ( old ) and ilford mgfb ) and i use asa 6 and get really good results ... YMMV



good luck with your tests!
john

 

[Photo Engineer]

Please see my post in the thread on paper negatives. It gives additional information on testing and getting better paper negatives than I did using MGIV. I was not trying for quality with a commercial paper for the reasons first mentioned here and also given in the other thread.

PE