Chemistry of Film Photography?

amolitor

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This is not high school chemistry, it turns out, it's pretty subtle stuff.

Quite a bit of it can be understood in terms of high school chemistry, but the business of latent image forming is not.
 

timor

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That, cause it only seems to be just a chemistry, but is molecular physics.
 

amolitor

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Well, there's a fair bit of chemistry, but most of THAT is about solubility of things in other things, which is a bloody mess as near as I can tell.
 
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tjc45

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Yes the latent image! All that business about photons moving electrons into lattice interstitial imperfections in the crystal surface and attracting silver ions and forming atoms blah blah blah WHAT DOES IT MEAN
 

timor

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It means, that creation of a latent image has some randomness in it. Something beyond regular human control. And here comes the QC of a maker to keep that randomness steady. Not every emulsion made even by Kodak had ever seen the store shelves, every production batch is slightly different and has own number. In production of a movie is essential to use film with the same emulsion number. In the past photographers were buying large quantities of film from one production run and tested it before shooting for keeps, important for the zone system but not only.
 

compur

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Yes the latent image! All that business about photons moving electrons into lattice interstitial imperfections in the crystal surface and attracting silver ions and forming atoms blah blah blah WHAT DOES IT MEAN

You are not the only one who is confused about how latent images are formed and developed as this excerpt from the book The Science of Photography by H. Baines & E.S. Bomback explains:

sciencephoto.jpg




As this excellent book further explains, when it gets right down to it, it isn't fully known for sure how this process works and the scientific explanations are really only theories and best guesses based on available evidence. (This is why I made my earlier comment about "magic.") What is known for sure is that light produces changes in the silver halides contained in a photo emulsion and developers exploit and magnify those changes. The book contains quite a lot of information about the theories concerning the changes and their development, far more information than could be posted here and it is worth reading. If you are curious I recommend you get a copy and read it. It is available used for pennies as you can see here:
Science of Photography: Harry Baines, Edward S. Bomback: 9780852422106: Amazon.com: Books


 

Compaq

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One way to think about the process is the following:

The film emulsion consists of silver halide crystals. When these are exposed to light, defects in the network/lattice are formed: metallic silver clusters. More light => larger clusters. These clusters are reaction centres when developing the film; the forming of the image is catalized by these clusters. Large clusters => black/dark area on negative. Small clusters (or non at all) => light grey (or blank) area on negative. Between different sized clusters, tonal ranges between black and light grey show after development.

This was a very simple explanation, without technical terms and jargon.
 

table1349

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Yes the latent image! All that business about photons moving electrons into lattice interstitial imperfections in the crystal surface and attracting silver ions and forming atoms blah blah blah WHAT DOES IT MEAN
It means two things.

1. Were not going to write your paper for you.

2. You need to spend some library time studying chemistry so you do understand and can complete your project.



Give a man a fish and you feed him for a day. Teach a man to fish and you feed him for a lifetime. Chinese Proverb

There are plenty of Chemistry teachers that have written books from which you can learn. Good luck.
 

Compaq

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If you really want to learn this in detail, you need to understand chemistry. There are written many textbooks in general chemistry. Such book covers a little bit of everything, and explains basic terms such as "ions", "solution", "lattice", "salt", "electron", "acid", "base", "pH", "reducing/oxidizing agent" and much, much more.

I have been studying chemistry for three years, and plan on continuing for at least two more years, so these terms are second nature to me. However, chemistry can be "self taught" provided you get good books and spend time learning.

Again, I am not sure how deeply you want to go into this.
 

EstherC

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Probably not. All that can really be done is to define all the terms, which is a lot of definitions.

Anyways. The point of a silver halide crystal is that it is inherently unstable. Hit it with light, and it breaks down a little into pure silver and pure halide. Just a little, usually (there are cases like "printing out paper" where it breaks down more thoroughly in normal usage).

Developer also breaks down silver halide crystals into pure silver and either pure halide of some other halide compound.

Developer has an easier time breaking down the crystals where light has given it a head start by breaking it down a little already.

So, if you develop for the right amount of time, the developer will mostly break down crystals that got hit with a bunch of light, and will mostly NOT break down the crystals there were left in the darkness.

Now you've got lots of pure silver where there was light, and very little where there wasn't.

Fixer dissolves silver halides, but not silver. Fixer leaves just the silver behind.

just wondering, sorry if it's a stupid question, do what you discuss here only apply to b&w film or color also?
 

danielklaer

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So this formula is correct?

Ag[SUP]+[/SUP]Br[SUP]-[/SUP] (crystal) + hv (radiation) --> Ag[SUP]+[/SUP] + Br+ e[SUP]-[/SUP]

yes but all that says is that silver bromide (a silver halide) breaks down in the presence of radiation to a silver ion, a free bromine atom and an electron. The free electron than meets your silver ion and forms a silver atom (this part of the reaction is Ag[SUP]+[/SUP] + e[SUP]-[/SUP] --> Ag).

You will need to do a bit of reading on your basic chemistry again as you need to at least understand what an equation says. Once you have reminded yourself of the basics there are plenty of resources, including this forum, where you can find out more specific info. It is very obvous when a student is just regurgitating what they have read without actually understanding it. Such an assignment would be marked accordingly.
 

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