Jump to content

Who formulates their developer?


giverin

Recommended Posts

All quite interesting, but ultimately quite pointless to know or worry about unless you're an emulsion chemist. Not many of them about today I'll hazard to guess

 

I am a chemist who shoots film, so I have a fair bit of interest in what's going on. It doesn't help, too, that my graduate degree/research was in nanonparticles and surface chemistry.

 

I wish our TEM wasn't seriously backlogged with only one person running it. Even when I was doing research and needed a TEM, it was a couple hundred dollars so I don't think he'd be open to running a piece of film for the heck of it. I do have access to AFM and SEM if I ask nicely(and can remember enough about how to run them, although the facility manager owes me a few favors). The grains are "buried" deep enough in the gelatin that I MIGHT not get decent topography from AFM, but SEM would probably work nicely.

Link to comment
Share on other sites

  • Replies 82
  • Created
  • Last Reply

Top Posters In This Topic

"...grains come in a variety of sizes."

 

- The thing is that nobody seems to know that for sure!

 

I've read every treatise I can find on the mechanism of development (that's not many), and none of them seem able to agree on exactly what happens during the development process, and exactly what form the reduced silver takes.

 

Best "guess" is by Ilford's chemists, who say that metallic silver filaments are extruded from the surface of the halide crystal. The filaments may travel some distance from their point of origin, or may curl back on themselves to form small balls. The speed of development influences the physical form of those silver filaments; with slower development keeping the filaments tighter to their point of origin, and therefore more compact.

 

In this model there would be little relationship between the size of the original crystal and the apparent size of the silver filament. Since the area of filament presented normal to the film would depend on its direction of growth, as well as its shape and volume.

 

This tallies reasonably well with the spidery tangle seen when viewing a developed B&W film through a microscope. It doesn't alter the fact that the image is made up of totally opaque parts with translucent areas in between.

 

All quite interesting, but ultimately quite pointless to know or worry about unless you're an emulsion chemist. Not many of them about today I'll hazard to guess.

 

Yes, I was thinking in terms of grain size before development. That is closer to the usual meaning of grain.

 

I usually think in terms of removing all the Br atoms, leaving lots of little holes, and not a solid grain of polycrystalline silver, but I suspect that, as you note, it is more complicated. I suspect that at some time there are lots of filaments going in different directions, but it still isn't obvious what the shape is. It still seems likely that more silver atoms make a bigger tangle of filaments, but maybe not so much bigger.

-- glen

Link to comment
Share on other sites

I am a chemist who shoots film, so I have a fair bit of interest in what's going on. It doesn't help, too, that my graduate degree/research was in nanonparticles and surface chemistry.

 

(snip)

 

One interesting thing that is related to surface chemistry (or surface physics) is dye sensitization.

 

Silver Bromide has a band gap appropriate for absorbing blue light, and so is sensitive to blue light, as were the early emulsions.

 

But if you adsorb appropriate dye molecules onto the surface, they can absorb other colors, and then inject electrons (or holes) into the crystal. That allows for films senstive to green, then red, and finally infrared. As I found out not so long ago, the original reason for adding dye was to reduce halation, reflections off the back of the film. But then the effect on extended sensitivity was discovered!

 

Some years ago, I was working in a semiconductor electrochemistry lab, and was supposed to know all these things, but understanding surface states was still always not so obvious to me.

-- glen

Link to comment
Share on other sites

I think that photo-chemistry is an area more than any other that resembles Schrodinger's cat (a generally stupid metaphor IMO), in that observing it changes its very nature.

 

One cannot simply poke any kind of microscope into a developing bath to see what's happening, and even seeing through the depth of a gelatine matrix presents problems.

 

It would be nice to see a 3D representation of the silver deposit or halide crystals, but about 20 years too late to be of any relevance.

Edited by rodeo_joe|1
Link to comment
Share on other sites

rodeo_joe, the Schrodinger's cat analogy to photography would be that film is in a camera but you don't know whether it has been exposed or not until you take it out and develop it.

 

Jim (big fan of the TV show "The Big Bang Theory" where Schrodinger's cat has been mentioned a number of times.)

James G. Dainis
Link to comment
Share on other sites

  • 6 years later...
On 5/18/2017 at 3:06 PM, giverin said:

I was wondering what the advantages and disadvantages of mixing your own developer from the base chemicals. I was reading about the two bath development method where you have to mix your own chemicals but I was also considering formulating my own D-76 because the price has increased quite a lot in recent years where I live. I know I'll have to buy some accurate scales but that isn't a big expense.

Yes!  I do this with most of the developers that I am currently making use of.

For a really good read...  Get a copy of the "Darkroom Cookbook".

https://silveronplastic.files.wordpress.com/2017/10/the-darkroom-cookbook-3rd-ed-s-anchell-elsevier-2008-ww.pdf

 

 

Link to comment
Share on other sites

  • 2 weeks later...

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now



×
×
  • Create New...