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Comment by vanderZwan | Hacker News Reader

Do you have any thoughts on how caffenol works, and how one might optimize this developer solution while keeping it non-toxic and ideally easy to create with simple household products? Or is Caffenol already about as good as it gets? On the caffenol website they don't seem to have link that explain the chemical process, but do mention that it's all about the phenols[0]. Which that in mind, wouldn't berry juice be a lot more effective?

EDIT: the Caffenol wiki page[1] has a link to the original article from 1995 explaining how this works[2]

[0] https://www.caffenol.org/alternative-recipes/

[1] https://en.wikipedia.org/wiki/Caffenol

[2] https://people.rit.edu/andpph/text-coffee.html

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In this interview the photographer says that he has used elderberry juice...

> I will surely continue exploring the wide world of edible and potable things like coffee, red wine, tea … made some successful experiments with elderberry juice, rosemary tea, coca cola … next will be dark beer for sure!

https://www.caffenol.org/2012/09/20/a-coffee-with-no-1-dagie...

One thing I'd be concerned about is lightfastness. This website

http://wilhelm-research.com/

tells the sordid story of how Kodak just didn't care about the permanence of color prints until 1980 or so. Wedding photographers would be paid $1000's for their work but couldn't get materials to make prints which would last a lifetime. Martin Scorsese lit a fire under Hollywood's ass about the permanence of films, but for that industry, keeping films in a dark freezer turned out to be a practical and permanent solution.

If you screw around with developing film with unusual chemicals I'd be concerned about how long the prints last, however black and white film where the image is really printed in silver crystals is likely to be more stable than the color film systems where the chemical changes in the silver crystals are coupled to dye systems.

When I was a kid I extracted dyes from flowers and did experiments with them and one conclusion was that they just don't last.

There is a ton of information on the internet but it’s a pretty straightforward chemical reaction process that you need to optimize:

- film has a silver halide emulsion in it

- silver halide converts to silver when exposed to light

- once you’ve taken your picture, you need to: 1) remove remaining silver halide that wasn’t exposed to light, 2) “fix” the remaining silver so it’s stable

The neat thing about chemistry is it’s very empirical. What your process is either works or not.

So would berry juice be better? Maybe? The only way you’d know is to try.

> - once you’ve taken your picture, you need to: 1) remove remaining silver halide that wasn’t exposed to light, 2) “fix” the remaining silver so it’s stable

There's a developing stage before before your step 1).

Developing causes areas of silver halide that were, in effect, only partly converted to silver (the so-called "latent image") to undergo full conversion. It's quite a complex process.

https://en.wikipedia.org/wiki/Latent_image

> once you’ve taken your picture, you need to: 1) remove remaining silver halide that wasn’t exposed to light, 2) “fix” the remaining silver so it’s stable

Isn't that somewhat backwards? The developer converts exposed grains to metalic silver to create a visible image from the latent one, the stop bath neutralizes the developing solution, and finally the fixer dissolves unexposed silver halide.

It works the same way any developer works, it takes the latent image formed in silver halide grains and converts them to metallic silver. Specifically the phenols in the coffee (tannins here) and the added vitamin c are the developing agents and the sodium bicarbonate reduces the ph enough for them to work. Other phenol containing compounds work, from walnuts to rosemary. There’s nothing special about coffee other than it’s cheap and readily available.

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