Chemical Disposal Quick Guide
At a Glance
| Symbol | Meaning | Action |
|---|---|---|
| 🟢 | Drain-safe | Dilute with water, pour down drain |
| 🟡 | Neutralise first | Treat before disposal, then drain-safe |
| 🔴 | Hazardous waste | Collect for professional disposal |
Black & White Processing
| Chemistry | Status | Disposal | Notes |
|---|---|---|---|
| Fresh developer | 🟢 | Drain | Dilute well |
| Exhausted developer (brown/black) | 🟢 | Drain | Oxidised = safer |
| Acetic acid stop bath | 🟡 | Neutralise | Add bicarb until fizzing stops |
| Water stop | 🟢 | Drain | Nothing to dispose |
| Fresh fixer | 🔴 | Haz waste | Contains thiosulfate |
| Exhausted fixer | 🔴 | Haz waste | Contains silver—NEVER drain |
| Wash water | 🟢 | Drain | Minimal contamination |
Colour Processing (C-41, RA-4, E-6)
| Chemistry | Status | Disposal | Notes |
|---|---|---|---|
| Colour developer | 🔴 | Haz waste | CD-3/CD-4 are aquatic toxins |
| Bleach (ferric EDTA) | 🔴 | Haz waste | EDTA is persistent |
| Fixer | 🔴 | Haz waste | Contains silver |
| Bleach-fix (Blix) | 🔴 | Haz waste | Contains silver + EDTA |
| Stabiliser (if used) | 🟢 | Drain | Modern formulas are benign |
Toning
| Chemistry | Status | Disposal | Notes |
|---|---|---|---|
| Selenium toner | 🔴 | Haz waste | Heavy metal—never drain |
| Sepia/sulfide toner | 🟢 | Drain | Dilute well; ventilate during use |
| Gold toner | 🔴 | Haz waste | Precious metal concerns |
| Iron blue toner | 🟢 | Drain | Ferric compounds are benign |
Experimental Processes
| Chemistry | Status | Disposal | Notes |
|---|---|---|---|
| Mordançage bleach (copper chloride) | 🔴 | Haz waste | Aquatic toxin; reuse indefinitely first |
| Chromoskedasic stabiliser (thiocyanate) | 🔴 | Haz waste | Collect even small amounts |
| Chromoskedasic activator (KOH) | 🟡 | Neutralise | Neutralise with weak acid, then drain |
| Lith developer | 🟢 | Drain | Same as standard B&W developer |
Alternative Processes
| Chemistry | Status | Disposal | Notes |
|---|---|---|---|
| Cyanotype sensitiser | 🟢 | Drain | Iron salts are benign |
| Cyanotype wash water | 🟢 | Drain | Prussian blue is non-toxic |
| Van Dyke brown fixer | 🔴 | Haz waste | Contains silver |
| Platinum/palladium chemistry | 🟢 | Drain | Noble metals are inert (but expensive) |
| Gum bichromate sensitiser | 🔴 | Haz waste | Dichromate is carcinogenic |
Neutralisation Procedure (for 🟡 items)
Acetic acid stop bath:
- Add sodium bicarbonate (baking soda) slowly
- Stir—it will fizz
- Continue until fizzing stops completely
- Test with pH strip if available (target: pH 6–8)
- Result is sodium acetate solution—drain-safe
Potassium hydroxide (chromo activator):
- Add weak acid slowly (vinegar works)
- Stir carefully—generates heat
- Continue until pH is neutral
- Result is potassium acetate solution—drain-safe
Key Principles
- When in doubt, collect for hazardous waste
- Never mix unknown chemistries
- Silver-bearing solutions are NEVER drain-safe
- Dilution is not disposal—it just spreads the problem
- Label everything clearly
Finding Hazardous Waste Disposal
- Municipal hazardous waste collection days
- Permanent drop-off facilities (check local council)
- Photo labs may accept fixer (for silver recovery)
- University/college chemistry departments sometimes accept small quantities
Sustainable Darkroom series