I've gotten requests to post a very high speed film formula. Well, I can't post an exact formula for obvious reasons, but I can speak in generalities about an ISO 800 - 3200 emulsion that I know about.

So, here goes. This will be a double run graded iodide core-shell emulsion.

First you must start with a low gelatin kettle of about 2% and high iodide, adjusted to between -200 and -250 mv in vAg.

Run into this dilute silver nitrate and dilute potassium iodide to maintain the vAg at the initial value throughout this nucleation. This can take from 1 - 10 minutes depending on flow rate and the amount of nuclei you wish to make.

Hold this kettle of nuclei while dumping in a gelatin solution such that the volume of the kettle is not changed much but the gelatin % rises to 5 - 10%. This is necessary for the next steps.

Run in some dilute silver nitrate to raise the vAg to the value selected to give either cubes, octahedra or t-grains.

Run in concentrated silver nitrate (about 10x the value of the first step) and concentrated potassium iodide (also about 10x the value of the first step). Ramp the flow rate up over about 1/2 hour in either a parabola or a linear ramp flow rate while keeping the vAg constant at this new, higher value. The type of ramp is dependant on the crystal type (cube, octahedra or t-grain).

While this ramp proceeds, ramp down the potassium iodide flow and begin ramping up the potassium bromide flow until at the end of the ramp there is no iodide going in and the salt flow is all bromide. During this ramp, the addition of Rhodium, Iridium and/or Osmium salts are done to tweak overall stability and reciprocity.

Then, dilute silver nitrate is run again to adjust the vAg to the final value. This is usually about +50 mv. The emulsion is washed and kept at about +50 mv.

The aim is to have a pure iodide core with a graded iodide shell and an overall iodide content of about 8 - 10%. The emulsion aim size would be about 8 microns. The final speed would make this useful as the fastest component of the fastest film you would ever want to make. This would place it in the range of up to ISO 3200. Speed is dependant on the type of sulfur and gold finish and the final addenda during finish.

Hope this gives more information to those requesting this type of formula, and also shows why it is difficult to do this type of thing at home.

You need a very well calibrated meter, and at least 3 if not 4 pumps for the solutions. Just the effort to fine tune such an emulsion will eat up a lot of silver nitrate.

Have fun thinking about this one.

PE

When I read these formulas you make it sound much more like an art than a science, kind of like winemaking. It must take a lot of skill and experince on the part of the emulsion maker to judge when things are "just right".

It seems to me that if film photgraphy goes the way of the dodo that a lot of this knowledge will be lost forever, kind of like how it seems impossible to duplicate Autochromes a century later.

According to my sources at George Eastman House, there are on average 6 contacts each year by people determined to reproduce Autochromes. To date, no one has done it. This includes the people who own the original autochrome equipment.

Your comment is apt here. I would tend to agree. After all, the Autochrome is 'revealed' in patents, so why can't we do it today? Well, this emulsion is 'revealed' in patents too. I say good luck to anyone who wants to duplicate it. It would take an expert, reading about 2 dozen patents to get all of the information in-hand, and then the experimentation starts.

PE

Patents certainly don't reveal everything about an invention. The basic premise of a patent is that in exchange for revealing the invention you get a monopoly on that invention for a specified period of time.

However, when I was a patent agent most of my clients wanted to reveal nothing and get a monopoly on everything. It was like pulling teeth to get them to tell me anything. I've never met a more paranoid group of people than inventors.

I do know that they got a patent on their process, but generally left out a crucial ingredient, or step in the process. The examiners at the patent office don't have the technical knowledge to know that a small, but vital piece was missing. It won't help future generations to make film if all they have to rely on is patents. Of course, as PE has alluded to, many of the ingredients or processes are kept internal as trade secrets and never published.

I know of a few ingredients published in patents without their true use being revealed. This is interesting in that a trade secret can be public but still be a secret.

I had an off-line argument with one of my detractors about using two of these ingredients in a certain way. He said it was stupid, but I knew otherwise. In the face of that kind of situation, all I could do was laugh.

PE

I knew I felt the earth shift on it's axis...and for good reason.

Thanks for the big leap forward, PE.

Now all we need are good vAg electrodes and a way to sub plastic without killing ourselves, and we'll be all set.

Bob M.

Bob;

Stand by on both of those. I'm working on them for y'all!

PE