How to Mix a Phenidone B&W Developer from Raw Chemicals
By Firstcall Photographic | Published: 2026-11-02
Category: How-to Guides
A practical, step-by-step method for mixing a phenidone black-and-white film developer from raw chemicals, including sodium sulphite, boric acid buffer, and a citric acid stop bath.
Quick answer
Mix a phenidone developer by dissolving the phenidone in a small amount of warm water first, then adding sodium sulphite as the preservative, and using boric acid with borax to buffer the solution. Always add the citric acid stop bath as a separate solution after development, never into the developer itself.
Why phenidone changes the mixing order
Phenidone is used at very low concentrations, so it must be fully dissolved before the other chemicals go in. If you dump sodium sulphite in first, the phenidone can clump or sit undissolved at the bottom, and the developer will be weak and inconsistent. Start with a small volume of water heated to about 40–50°C (104–122°F), dissolve the phenidone completely, then add the sulphite.
Sodium sulphite anhydrous is the workhorse here: it protects the developer from oxidation and acts as a mild silver solvent in fine-grain formulas. Because it is anhydrous, it dissolves readily but can pull moisture from the air, so weigh it quickly and keep the container sealed.
The buffer and the stop bath are separate jobs
Boric acid combined with borax creates a buffer that holds the developer's pH steady during use. That matters with phenidone because its activity is very pH-sensitive; a small drift changes contrast and development time. Mix the buffer into the developer only after the phenidone and sulphite are fully dissolved, and check that the pH is in the expected range before you develop film.
Citric acid is not a developer ingredient. It makes a low-odor stop bath that neutralises the alkaline developer and halts development quickly. Keep it in a separate tray or tank; adding it to the developer would acidify the solution and stop it working.
When a simpler route is the better choice
Mixing from raw chemicals gives you control over grain, contrast, and cost per roll, but it also means you own the measuring, the water quality, and the pH checks. If you are new to darkroom work, a pre-measured developer kit removes most of the variables while you learn your film and exposure. Move to raw chemicals once you can consistently hit your target contrast and want to tune a formula.
Also consider your water. Hard water can interfere with dissolution and buffering, so use distilled or deionised water for the concentrate if your tap water is heavily mineralised.
Step-by-step: mixing and using the developer
- Prepare your water and workspace: Measure about 750 ml of distilled or deionised water and warm it to roughly 40–50°C (104–122°F). Set out your scale, graduated cylinders, and stirrer, and wear gloves and eye protection. Do not use hot water above 50°C; phenidone can degrade and the sulphite dissolves less predictably.
- Dissolve the phenidone first: Weigh the phenidone according to your formula and add it to the warm water while stirring. Keep stirring until no particles remain visible. Check the bottom of the vessel for undissolved phenidone before proceeding; if you see specks, stir longer or warm slightly.
- Add the sodium sulphite: Weigh the sodium sulphite anhydrous and add it gradually to the phenidone solution, stirring continuously until fully dissolved. Weigh the sulphite quickly and reseal the container; anhydrous sulphite absorbs moisture from the air.
- Mix and add the borate buffer: Dissolve the boric acid and borax in a small amount of warm water separately, then add that buffer solution to the developer while stirring. Add the buffer only after the phenidone and sulphite are fully dissolved, or the buffer may prevent complete dissolution.
- Top up and check the volume: Add water to bring the developer to its final volume, stir gently, and let it cool to working temperature before use. Measure the final volume at room temperature; warm solutions expand and can give you a more dilute developer than intended.
- Mix the citric acid stop bath separately: In a separate container, dissolve the citric acid monohydrate in water according to your stop bath ratio. Label it clearly and keep it away from the developer. Never pour the stop bath into the developer; even a small amount will acidify the solution and ruin it.
- Develop, stop, and fix in sequence: Pour the developer into the tank, agitate according to your formula, then pour it out and add the citric acid stop bath. After stopping, fix and wash as normal. Use a separate graduated cylinder for the stop bath, or rinse the developer cylinder thoroughly before the next mix.
Chemicals used in this mix
- Bellini Sodium Suphite anhydrous - 1kg: Sodium Sulphite anhydrous is a developer preservative and a mild silver solvent in fine-grain developers. It protects the phenidone developer from oxidation and contributes to finer grain, so it is added after the phenidone dissolves.
Bellini Sodium Suphite anhydrous - 1kg - Bellini Boric Acid - 50g: Boric Acid acts as a solution buffering agent when used with Borax. The borate buffer keeps the phenidone developer's pH stable, which keeps development times and contrast repeatable.
Bellini Boric Acid - 50g - Bellini Citric Acid Citric Acid Monohydrate - 250g: Citric Acid is often used as a lower-odor stop bath when developing photographic film. It stops development cleanly without the strong smell of acetic acid, but it must be mixed as a separate bath.
