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Making your own film

Making your own emulsion

I do not find the formula that you say you have posted . Forgive my stupidity as I am a newcomer to the web.
As for coating it, I have observed better results at my leisure here than during a workshop. I have now isolated the problem. In the rush of giving the workshop, the film and plate coatings are used within 24 hours to fit it into the course. It turns out that this introduces micro reticulation into the coating as the hardening is not complete. It also allows for more frilling especially on glass plates.

In addition, the contrast varies comparing ones done here and ones done in workshops. The latter are considerably lower than what I get here at my leisure. Well, in the haste of the workshop, the ammonia-silver 'digest' is given 3 days or more, but in class it is given, at best, 2 days. This lowers final contrast considerably.

So, long and slow is the deal with the 'real formula' posted below to get optimum contrast and speed.

Now, about coating. I think that the film will have to be coated at about 25% greater silver per unit area than I currently use. I'm working on that.

In addition, it will probably be impossible to get useful coatings on 120 size film. Sheet film of 6x7 and up is possible with probably 11x20 being the largest practical size. The smaller sizes will be sharp enough, but grain will probably be bad. From 4x5 up, the grain and sharpness will be quite good.

If one accepts a speed of about 12, then you will have fine grain and good sharpness in plates and films down to about 6x7.

I am giving the plate coater a good workout and it seems to do well. If it works out, this plate coater will simplify all plate coatings. I'm currently working on a method to allow one blade to do all sizes of plates, but that may not be possible. Right now, I can do only 4x5 plates.

I have tried to answer most of your questions in one post here.

PE[/QUOTE]
 
lsk;

I'm not sure what you are trying to say, but I have posted a film formula in this forum. It is what we called an SRAD (Single Run Ammonia Digest) emulsion. In a good run, I can achieve an ortho sensitive emulsion with and ISO speed of 40. I have posted some results here that were obtained by my students.

PE
 
Thanks for coming back to me ! Is there any way I can go back in this thread to find your film emulsion formula and also a paper emulsion formula?I have never used forums before so I am really all thumbs here !
Many thanks,lsk.
 
Lsk;

Try the search option. That might help. For obvious reasons I don't search my own name. I'll try to find it and post the URL though so that it can help you.

PE
 
what is meant by 'continuous precipitation"?

Hello PE,

I ran across the phrase "continuous precipitation" while reading the Duffin book "Photographic Emulsion Chemistry" (page 57, if you have it). I am not sure what this is referring to. The mention of it in the book assumes the reader is aware of the definition, and how it is applied, as I haven't found an explanation in other parts of the book (so far).

Is this term a reference to another method of mixing emulsion ingredients?
Is it the proper name for the reaction of the ingredients when they are introduced into a mixing vessel?

Can you please explain what "continuous precipitation" is?

(If this was discussed here as part of another thread, please point me in right direction).

Thanks,

Bob M.
 
Ingredients flow in one end and the final emulsion flows out the other end without stopping as opposed to a batch process.

Except for Wey and Whitely, which is a close approace to this method, it was never commercialized by any company AFAIK, and remains a patent curiosity. All emulsions are made today using the batch process.

PE
 
PE,

Can you please discuss the how, what, and why of an 'interlayer', which has been mentioned re: color emulsions? Are interlayers used in B&W film / paper, for perhaps different reasons?

I have also come across references to a 'supercoat', particularly when shown in a cross section of film. Is a supercoat a layer of hardened unsensitized gelatin used as a final outermost layer of emulsion, or is it something altogether different?

Thanks,

Bob M.
 
In Anchell, he defines a supercoat as a non-hardened overcoat that washes off. This is incorrect. It is hardened and is plain gelatin or gelatin + absorbing dyes depending on fim.

The reason for a supercoat is this. During coating, the master roll is 'cinched' rather tightly and can abrade the top of the emulsion layer causing defects such as scratches and actual fog due to abrasion of the silver halide crystals. The overcoat acts as a protective 'glove' over the surface.

Interlayers are generally only used in color films and their purpose is to isolate each layer from another to prevent cross color contamination by wandering oxidized color developer. Without interlayers, the individual colors resemble blue, grape and pumpkin instead of cyan, magenta and yellow. These interlayers contain special chemicals to mop up oxidized color developer.

PE
 
PE,

Thank you for that explanation. It clears that up nicely.

One purely hypothetical question (only for the sake of discussion, not actual planning)

If an emulsion mix is a suspension, and not a solution, could an emulsion mix could be put into a centrifuge to "settle' the larger grains towards the bottom of the centrifuge container, and leave the smaller grains near the top to be siphoned off?

I do realize this is not how one 'preferred' size of grain is grown, but was wondering what might happen.....before I commit the family washing machine to double as a centrifuge on the spin cycle (just kidding....really).

Thanks again...

Bob
 
Bob;

Centrifuging emulsions is indeed possible and has been demonstrated, but was never reduced to a practical concept because building a monodisperse emulsion of any desired size and shape is so easy using modern methods.

I thought I had mentioned that elsewhere, but I know that it is discussed in some of the texts. Here is one suggestion. Going up in temperature increases grain size, and going down, decreases grain size. Even addition rates at any given vAg with good control and no pulsation with a combination of other things will give you anything from a 0.1 micron to a 10 micron grain with a shape from cubic to t-grain as desired, and with a monodisperse or a polydisperse nature.

PE
 
flexibility of emulsions

Hello PE,

Can you please tell me if emulsion, after it is coated, is flexible, and to what degree? If you are coating paper or film, the support is, for the most part, dried and used flat, without being flexed greatly. Can the emulsion you use in your workshops be used "as is" on a more flexible substrate, or would extra steps (or ingredients) be needed to make the emulsion flexible enough to withstand use on a less rigid support without cracking or chipping?

The emulsion on the matrix film I had written about earlier had chipped when I cut a section out of a larger sheet, even though it was coated on a flexible support (7 mil polyester). I am not sure if this was a result of emulsion thickness, emulsion composition, or age of the sample.

I have also examined old rolls of film (10+ years) which did not show any adverse effects when unbent or re-rolled, and there were no chipping or cracking effects noted when the film was cut with scissors. Is there some other ingredient used in commercially produced film that is outside of the scope of hand makng and coating emulsions, or is this a benefit of more advanced making methods?

Thank you,

Bob M.
 
I have had no problem with my emulsions chipping or cracking.

Generally, sorbitol or glycerine are added to prevent this.

PE
 
Emulsion speed determination

Hello PE,

Can you please discuss how the speed of the finished / coated emulsion is determined?

Thanks,

Bob M.
 
Bob;

We have carefully calibrated densitometers which are used to give an exposure to the newly made emulsion. The speed is measured using an internal measure called CR speed. Offhand, I forget the meaning of the acronym. In any event, it is expressed as a 3 digit # which can be converted to ISO speed.

The means I have to resort to now is to expose one of my emulsions at different exposures and match it with the same exposure of a known product and compare the results. The step wedges tell me how I compare with the product, and so I can say that my Azo like paper is close to Kodak Azo (see Alex Hawley's review) and I can say that my Bromide enlarging paper is like Ilford MGIV.

For film exposure, we expose the film using a meter and the best exposure wins. The film is generally variable and low in contrast, but different emulsions are optimum at from ISO 3 - 50 on film support.

PE
 
PE,

I thought it was more involved than that, but this pretty straightforward.

Thanks,

Bob M.
 
Acquiring materials....

Hello all,

I am in the process of getting together materials and supplies to make and test emulsions. I do not have access to a large format camera (4x5 or 8x10) to make a few exposures to use for contact printing to test paper emulsions. I have been advised that I can use step wedges, but I would like to use a negative of, say, an outdoor scene, to give me something more to work with. I am looking for 2 4x5 and 2 8x10 B&W negatives of still life, street scenes, nature, etc, etc. whatever has a wide range of contrast. If someone has 5x7 negs they can be put to use as well. If a list member can assist, please let me know here, or privately at rmazzullo@si.rr.com.

Thanks,

Bob Mazzullo
 

Bob;

For test purposes a digital 4x5 or 8x10 negative of any smaller format will work just fine in the interim to get you started. The object is to have a reference print on a regular paper to insure you have standardized the digital negative for these limited test purposes.

PE
 
Hello PE,

Thanks for the excellent suggestion. I hadn't considered using digital negatives for this purpose. Making a print on regular paper as a standard for basic testing will fit the bill nicely.

Bob M.
 
Hello PE,

During the noodle washing step there is a test that can be performed to determine if enough salts are washed out of the emulsion. Can the same test be used if ultrafiltration is done instead of noodle washing?

Thanks,

Bob
 
Bob;

Yes, there is a test. Use the silver nitrate test for hypo retention. Take a beaker of the spent wash water (about 50ml) and add a drop of silver nitrate to it. If a heavy precipitate forms, the emulsion is not washed enough, but if i just turns cloudy it is washed well. If it is clear, it is washed but may be just a bit over washed.

If it contains ammonia, there must be no ammonia odor.

PE
 
PE,

Thank you for the test tip.

This is another one of those hypothetical questions about emulsion coating, but this time you can blame one of those popular multi-stripe toothpastes.

Assume that you have 2 tested emulsions, one slow speed, one higher speed. You are able to make good coating formulas for both.

If a double trough coater is used, one trough for each emulsion, and the slot setup to deliver one emulsion on top of the other as the coater is pulled (or pushed) along the substrate, would it be possible to deposit a double layer of emulsion at the lower speed of manually moving the coater along the support, without mixing the two layers? Would some sort of positive pressure be needed to evenly push the emulsions through the slot, or would surface tension "pull" the double layer through and along the support?

Aside from what you have already mentioned, that you would coat one layer and let it dry before coating another in a Kodak test environment, and that slide and / or curtain coaters need to run at high (very high?) speed to work, would the principles / physics that govern emulsion coating have enough leeway to (potentially) allow this?

Thanks,

Bob
 
You can probably do this, but I would think the defect rate would be high. Gravity would pull the emulsion through the coater as it does with a coating blade. Whether the two layers would stay separate well enough, IDK.

In a case such as you describe though, I would opt to blend the emulsions together rather than coat 2 layers.

PE
 
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