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.