Negative Processing Chemistry Research
Some links to lower-toxicity recipes for dev/stop/fix, with some price and source exploration:
Chems
Dev
Ascorbic Acid (vitamin C)
225g - $13 - ebay - $0.057/g
1000g - $40 - ebay - $0.040/g
500g - $23 - ebay - $0.046/g
450g - $35 - ebay - $0.077/g
225g - $17 - ebay - $0.075/g
450g - $20 - ebay - $0.044/g
900g - $30 - ebay - $0.033/g
Sodium Carbonate (Soda Ash)
500g - $40 - ebay - $0.080/g
680g - $37 - ebay - $0.054/g
1000g - $30 - ebay - $0.030/g
100g - $5 - ebay - $0.050/g
500g - $12 - ebay - $0.024/g
Stop
As the developer isn't as aggressive, we can get away with water bath for stop.
Fix (non-hardening)
Sodium thiosulfate (pentahydrate/crystalline)
400g - $37 - etsy - $0.0925/g
113g - $7 - ebay - 113g – $0.0619/g
2500g - $50 - ebay - $0.0200/g
1360g - $55 - ebay - $0.0404/g
1360g - $50 - ebay - $0.0368/g
450g - $15 - ebay - $0.0333/g
Sodium sulfite (anhydrous) - Increases shelf-life of fix, not necessary
30g - $40 - ebay - $1.33/g
500g - $150 - ebay - $0.30/g
500g - $50 - ebay - $0.10/g
450g - $30 - ebay - $0.07/g
450g - $23 - ebay - $0.05/g
225g - $16 - ebay - $0.07/g
450g - $14 - ebay - $0.03/g
100g - $10 - ebay - $0.10/g
Articles
https://petapixel.com/caffenol-developing-film-with-coffee/
Possibly with espresso given that we have coffee roasting and an espresso machine?