View Full Version : Notes on and an account of "making a simple photographic emulsion"

10-15-2006, 02:33 PM
Greetings all,

I've been so busy with school that I've not had any time to do more than lurk on APUG, but I've got some free time this Sunday morning. :)

I spent the majority of yesterday in the darkroom making the "simple photographic emulsion" as it appears on UnblinkingEye.com's front page, which I've heard is either an adaptation of or is practically the same thing as Kodak's publication AJ-12. The characteristics of this emulsion are its low speed, blue sensitivity, medium contrast, and simple formula, which consists of only four ingredients, or five if you include water. :)

I started at about noon, took a break at 2:30 to allow the emulsion to set, came back at 5:30, and was out the door just after 8:00 PM. So while it took about five hours of lab work, I was basically tied up for the whole day. I figured it would take this long, but I hadn't counted on some of the steps being so stubborn. Who knew dissolving gelatin could take 20 minutes of stirring? But I'm getting ahead of myself.

Here are my notes from the process, alongside a summary of the steps.

I made a half-batch. I had pre-measured my chems into ziploc baggies a few days prior, which I then cut open when it was time to pour. Instead of working with granular potassium iodide, I used a 5% solution. My gelatin was from the Photographer's Formulary, with a BI of 250. Also, there's a distillery on campus from which I filled three large water jugs with 27 liters of DI water, which was just a little more than enough. ALL my water, save for that in the water bath, came from this supply.

I could not find any cheesecloth. Where does one buy cheesecloth? (And why would anybody make their own cheese in these modern times!?) Instead, after some deliberation, I went to the hardware store and got some fiberglass window screen, which smelled like vinyl. Concerned about contaminants, I washed the material in several changes of hot water until the vinyl smell went away, then gave it a final rinse in distilled water.

Lastly, I'm not a chem student, I just pretend to be one on the weekends, so my amateur technique might induce cringes to those of you who know what you are doing. Feel free to suggest refinements, I'll take all the help I can get!

1. Dissolve initial gelatin in warm distilled water.
Took forever, even as I warmed the beaker and water bath apparatus, a glass pyrex bowl.

2. Add KBr and KI to gelatin solution and stir until dissolved.
Simple. Since I was working with a 5% solution of KI I accounted for this extra volume (8ml) when I measured out the initial distilled water for step 1.

3. Heat the solution to 130F / 55C and hold it there.

4. Lights out.

5. Make a solution of silver nitrate.

6. Add silver nitrate solution to gelatin mixture, slowly.
This is the most dramatic step. The whole solution turns white and opaque, not unlike coconut milk. I added ~10ml every 30 seconds for 10 minutes, stirring constantly. Note to self: next time, ask for a hot plate with magnetic stirring device.

Question: the silver nitrate solution was at 16 degrees celsius, while the gelatin mixture was at 55. Even as slowly as I did this step, the temperature of the resulting mixture dropped with every pour cycle and the final product had to be brought back up to temperature before I could proceed with step 7. Should step 5b be, "bring solution of silver nitrate up to temperature?"

7. Ripen the mixture - hold it at 130F / 55C for 10 minutes, then allow to slowly cool to 104F / 40C.
Difficult, even with a fairly adjustable hot plate. My impatience here caused the temperature to swing more than I would have liked, all the way to 58 degrees celsius before I pulled the beaker out of the bath to prevent it from overheating. I'm aware that the temperature at this step is crucial, so I'm a little bummed about this.

8. Swell additional gelatin.
Wasn't sure how much water to swell the gelatin with, so I put 20 grams at the bottom of a 300ml graduate and filled it with water.

At this point, while the emulsion cooled and gelatin swelled, I took a break for a quick bite to eat. When I returned about a half hour later, the gelatin filled almost the entire graduate. My silver halide mixture was almost exactly 104 degrees.

9. Combine solutions (emulsification), mix thoroughly, allow to set for 2-4 hours.
Okay, so I poured the excess water out from the newly swollen gelatin and dumped it into my "reaction vessel," which I then stirred for awhile. I put the water bath back on the burner to help dissolve the new gelatin. When it seemed the mixture was homogeneous, I pulled the beaker out of the water bath and put it in a lightproof cabinet to set.

The time was about 2:30.

Trying to visualize the next few steps I became concerned that my water wouldn't be cool enough to do the wash step properly. I took two jugs of water home with me and let them sit in the fridge for three hours while I did stuff around the house.

I returned at 5:30.

The emulsion had set, it shook around like white jell-o.

10. Strain the emulsion through cheesecloth.
This is where things started to get very dicey indeed. I put my freshly rinsed screen material over a plastic 1-gallon beaker and tried to dump the emulsion into it. It wouldn't come out, it was stuck in the beaker. Hmm.

Plan "A" was to get the water bath hot and put the emulsion beaker in it just long enough to melt it free. I put the burner on "HI" and put the water bath on top.

Abruptly, the pyrex bowl cracked in half.

Ha ha! I thought. Funny joke! But it really was leaking, the water was seeping through the crack and hissing on the burner. Quick, time for a plan B.

Plan B: rinse a thermometer in distilled water, then use it to separate the emulsion from the sides of the beaker. This actually worked, the emulsion broke free and I gathered up the screen and squeezed the lump into the beaker.

What has been described as the "spaghetti" stage would have been more aptly described as the "ricotta cheese" stage, in this instance.

11. Leech out excess silver salts by pouring three liters of cold water onto the emulsion. Allow it to sit and settle for 2.5 minutes, then pour off 2 liters of water and add 2 more.


12. Repeat this five times.

Okay. Did it six times, for good measure.

13. Melt and after-ripen, heat to 130F / 55C and hold for 15 minutes.

There's an important step missing between 12 and 13. Once you've spaghettified the emulsion and dumped water on it, the sludge doubles in size, even after you've poured off as much excess water as possible. What had been about 550 ml of emulsion had turned into 1 full liter. The missing step is to re-strain the emulsion to get the excess water out of it. I did this, then put it back into the beaker by squeezing it through my screen material. This was wasteful and represented yet another risk of contamination, but I had little choice.

At this point I left the room to get a stainless steel bowl to replace my ruined pyrex.

For the final melt and after-ripen, I was much more cautious with the temperature, and melted it slowly. I managed to hold it at temp for 15 minutes, with good accuracy. I saved the final product in a black bottle and put it into a light-proof bag for good measure.


I haven't had time to test the emulsion yet but I feel fairly confident that none of my mishaps were drastic enough to ruin it. Today I'll see about getting an ersatz plate holder working (I'm trying to make one from an old graflex film pack magazine). With any luck, I should be shooting plates by the end of next week. If that doesn't work, well, I can always coat paper negatives...

Please send me your suggestions, comments, or questions.

--Conor Peterson

10-15-2006, 07:16 PM
A very interesting account of your adventures. Thanks for sharing with us. I look forward to hearing about your testing. You weren't using your home kitchen, were you?

Photo Engineer
10-15-2006, 07:37 PM

Thats much too complicated, and the Kodak formula leaves out some important facts.

The emulsion should be diced after chill setting unless you use a potato ricer. If you do use a ricer, it must be heavy duty.

The emulsion can then be washed in ice cold distilled water using a piece of the toe portion of panty hose.

You wash the diced emulsion in DW and then wring it dry by squeezing the panty hose with a twisting motion to wring out the excess water. The emulsion will always become more dilute in this step. This is why I use another method entirely, but EK didn't want to publish this method for some reason.

Now, when you test the emulsion, it will be about 3 - 6 ISO speed due to the lack of sensitization. Modern photo grade gelatin does not contain any sufur compounds in it, and food grade, with these sulfur compounds has so many additives that it is unusable.

I've basically updated this quite a bit and the formula I post in this forum gives much information on this.

You have to wash until there is virtually no indication of halide in the wash water. You can test for this by taking some wash water and dropping in a drop of silver nitrate solution. If it is cloudy, then there is too much halide present. If you smell ammonia (I cant remember if this formula uses ammonia or not) then it is not washed enough regardless of the silver test.

If there is an ammonia odor, then hardeners used when you coat the emulsion will not work properly as the emulsion is too alkaline. You may want to adjust the pH in that case to about 6.5 with 5% sulfuric acid.

When you add the silver nitrate to the salt, they should be at the same temperature or you need a good heating system to maintain the temperature. When making large batches of emulsion, we had the opposite problem. They would tend to heat up when the reaction takes place. This entire exercise in temperature control is called 'enthalpy' and is a very important subject in emulsion making.


10-16-2006, 12:07 AM

No need to work in the kitchen, I got some keys to an unused darkroom at school. I had to mop the heck out of the space to clean up all the dust, but it's mine for the duration of this project. I'll attach some pictures! I wish I had shot some of the actual process, but it would have been too messy.

Incidentally, I did develop some of the spill mat today that had absorbed some of the liquefied emulsion. It turned black. So that's almost like testing it! And I'm halfway to getting the plate holder working, so I'll hopefully have some actual results to post soon.

Oh boy. I wish I could take you out for a beer and absorb some of your knowledge.

Can we first discuss washing technique? I felt like that was the most inaccurate, dubious part of the whole process, and if I were to improve something, that would have been it. The way I just did it seemed wasteful and ultimately diluted the emulsion more than I think it should have.

Your method of dicing the emulsion and then rinsing it in the tip of some hose sounds too good to be true. How finely does the emulsion need to be diced in order for this method to be effective? Would I just rake a scrupulously clean knife through the chill-set emulsion until it was thoroughly scrambled?

There was no ammonia component to my emulsion but I noted that you include some in your recipes. I briefly looked over them earlier today, just after making my original post. So, since I added no ammonia, I can expect lower speed, but on the other hand, I should be able to harden it, right?

That brings up another thing I wanted to ask: hardening the emulsion prior to coating. I have a 5% solution of potassium dichromate leftover from the van dyke kit I played with this summer. Should I put some in a small tray and "float" the coated plates on it for a few seconds? Or is there a better, less carcinogenic way that I might approach this? I also have access to C-41 stabilizer if that's of any use (formalin?), and the hardening component for the lab's b&w fixer.

Should I even be worrying about hardening the emulsion at this point?

Guess I still have a lot of stuff to think over. I think I'll sleep on it. :)

Good night all,

Photo Engineer
10-16-2006, 09:06 AM

I use 1/4" to 1/2" cubes when dicing. Wash times are longer this way than using a potato ricer due to the lower surface area.

Effectively, ammonia in an emulsion churns the iodide to the surface of the grain, or at least distributes it more evenly in the grain than otherwise, and this raises speed. It can also raise fog. There are other ways to improve the emulsion making than either method, but iodide does help speed a bit in the emulsion you describe. I have not read the formula for quite a while.


Use either of the following, formalin, chrome alum or glyoxal.

I use the latter two at the rate of about 5 ml of a 10% solution for every 100 ml of 10% gelatin. You have to adjust accordingly. On film support, these will take about 24 hours to harden, but on paper support it will tak about 4 hours to harden.

On film support you will see an ISO speed of 3 - 6 if you are lucky, but if you coat on paper support and make paper negatives, it will probably have an ISO speed of up to 25 due to multiple internal reflections from the backing paper, and it will be less sharp. The speed will depend on laydown on both film and paper, and on paper it will also depend on the nature of the back reflection.


10-28-2006, 07:42 PM
First batch of plates was a disaster; coating is very difficult. The emulsion was coated so thinly that the image was just barely visible. I'm going to re-coat some tonight.

But here's a scan of my first print from my first plate (which has a little added tone in photoshop).

I'd be lucky if this was even ISO 3.

Photo Engineer
10-28-2006, 07:49 PM
Quite good for a first try. The circles are called repellancy spots and can come from either grease or oil spots on the plate or insufficient wetting agent in the emulsion. Often a wetting agent like TX100 or TX200 are used at about 0.5 cc / 100 ml of 10% gelatin. You can also use alcohol, but it is less efficient.

The low density is common with unfinished (sulfur treated) emulsions or with emulsions that are too dilute.


10-28-2006, 08:18 PM

10-29-2006, 01:37 AM
Oh relax, its still better than my first dry plate--and that was with store bought emulsion. Keep it up!

First batch of plates was a disaster; I'd be lucky if this was even ISO 3.