D-23

D-23 is Kodak's minimalist film developer — just two ingredients (Metol and sodium sulfite, no alkali accelerator, no restrainer) — published continuously since at least the 1940s and still actively used by film photographers in 2026. Where most film developers contain 4-6 ingredients balanced for specific characteristics, D-23 demonstrates that effective B&W development can be reduced to its essential chemistry: a single developing agent (Metol) and a single preservative-mild-alkali (sodium sulfite at high concentration).^[1]

The compositional simplicity is D-23's signature feature — and the source of its versatility. Unlike heavily-buffered developers like D-76 or HC-110 where chemistry dictates one optimal use case, D-23's two ingredients can be used as-is for routine work, diluted for compensating high-contrast development, paired with an alkaline second bath for two-bath split-developer workflows, replenished indefinitely for cost economy, or modified with additives for specific characteristics. Ansel Adams cited D-23 variants throughout The Negative as the developer of choice for high-contrast scenes where preserving highlight detail mattered.^[2]

D-23 is mixed from powder ingredients to one liter of stock solution. Stock can be used full-strength for routine development, or diluted 1:1 or 1:3 for compensating effects.

When to choose D-23 over D-76

D-23 is most often weighed against D-76 (the "next-step-up" buffered developer) and HC-110 (the convenience-concentrate alternative):

• vs D-76: D-76 adds borax accelerator and Hydroquinone for higher activity at the lower-density grains, plus more predictable highlight rendering. Choose D-76 for routine box-speed development where consistency matters; choose D-23 when you need the compensating dilution variants or want to experiment with two-bath workflows. Many photographers use both — D-76 for routine, D-23 for high-contrast scenes.
• vs HC-110 Dilution H (1:63): HC-110 at very dilute strength serves a similar compensating role to D-23 1:3. Choose HC-110 H for the convenience of liquid concentrate; D-23 1:3 when you want longer development times (D-23 1:3 typical 18-24 minutes vs HC-110 H's 10-12) for finer visible-grain rendering or stand-development workflows.
• vs Pyrocat-HD: Pyrocat-HD is the "modern compensating developer" — staining mechanism gives compensation without the speed loss D-23 1:3 produces. Choose D-23 when avoiding stain (ease of scanning, hybrid workflows); Pyrocat-HD when the stain serves your printing goals (alt-process, higher contrast at the negative).
• vs Diafine: Diafine is the locked two-bath alternative — predictable across films, very long shelf life, no dilution choices. D-23 + Kodalk two-bath (DIY equivalent) is more flexible (you control bath times, dilutions) but more complex to manage. Choose Diafine for simplicity; D-23 two-bath for control.

The minimalist chemistry — two ingredients, many configurations

D-23's two-ingredient formula uses Metol as the sole developing agent, with sodium sulfite (typically 100 g/L — very high concentration) serving three distinct roles:^[1]

1. Preservative: protects Metol from atmospheric oxidation, giving D-23 stock excellent shelf life
2. Mild alkali: sulfite raises pH to ~8.0 (D-76 reaches 8.5 with borax; Dektol reaches 10.5 with carbonate) — enough to activate Metol but gentler than carbonate-buffered developers
3. Solvent: at 100 g/L concentration, sulfite partially dissolves silver halide grain edges (the same fine-grain mechanism as D-76), producing fine grain in the negative

The absence of Hydroquinone means D-23 never reaches Dektol-level highlight contrast — but for film photography this is a feature, not a bug. The gentle highlight rendering preserves shadow-to-highlight ratio better than aggressive developers, especially for high-contrast scenes (sunlit landscape, bright-window interior, snow with shadow detail).

The variant family — D-23's defining versatility

D-23's true power is in its dilution and modification variants. Standard reference development times for HP5 Plus or Tri-X at EI 400 in 20°C:^[1]

Configuration	Working dilution	Typical time	Use case
D-23 stock	Full strength	7-9 minutes	Routine box-speed development
D-23 1:1	One-shot dilution	11-14 minutes	Slight compensating effect; finer grain than stock
D-23 1:3	Highly dilute	18-24 minutes	Strong compensating; high-contrast scenes; semi-stand workflows
D-23 + Kodalk two-bath	Stock D-23 (5 min) → 10g/L Kodalk (5 min)	Two-stage	Maximum compensation; legendary "Adams two-bath" approach for difficult contrast
D-23 replenished	Stock + 70 ml replenisher per roll	7-9 min (unchanged)	Long-term economy; some labs run D-23 stock for years with replenishment

The two-bath D-23+Kodalk workflow (sometimes called "Adams two-bath" or "D-23 split development") is the configuration most associated with D-23 in modern usage. The film soaks in D-23 stock (with no alkali accelerator) for 5 minutes, then transfers without rinsing to a 10 g/L Kodalk (sodium metaborate) bath for 5 minutes. The Metol carried in the emulsion from bath 1 develops aggressively when it hits the alkali in bath 2 — but only where there's enough Metol left to develop, which is the lower-density (highlight) regions. The result: shadows develop fully in bath 1, highlights develop only as long as Metol remains in the emulsion in bath 2, producing automatic highlight compensation without sacrificing shadow detail.

Practical notes

• Mix from individual chemicals: D-23 is rarely sold pre-mixed; assemble from individual ingredients (7.5 g Metol + 100 g sodium sulfite per liter of stock). Both chemicals are inexpensive and widely available.
• Mix Metol first: dissolve Metol in 750 ml of water at 50°C before adding sulfite. Adding sulfite first or simultaneously prevents Metol from dissolving (sulfite-saturated water is a poor solvent for Metol). Then add sulfite, stir to dissolve, top up to 1 liter.
• Stock keeps 6+ months in tightly-sealed full bottles; partial bottles oxidize within ~3 months despite the high sulfite content.
• D-23 1:3 working solution is one-shot only; do not store diluted solution.
• For two-bath D-23+Kodalk: do NOT rinse between baths. The whole point is to carry Metol from bath 1 into bath 2 to drive the compensation effect. Mix Kodalk bath fresh for each session.
• PPE: Standard developer-handling — nitrile gloves and eye protection. Metol is a known sensitizer; D-23's high Metol-to-other-chemicals ratio makes prolonged skin contact slightly higher-risk than balanced developers.

Related recipes

• [[recipe-d-76|D-76]] — the "next-step-up" buffered MQ alternative; the routine-work counterpart
• [[recipe-hc-110|HC-110]] — concentrate alternative for compensating dilutions; the convenience option
• [[recipe-pyrocat-hd|Pyrocat-HD]] — staining-developer alternative when stain helps the printing workflow
• [[recipe-diafine|Diafine]] — locked two-bath alternative; simpler but less flexible
• [[recipe-microphen|Microphen]] — speed-increase alternative for push processing (D-23 does not push well)
• [[recipe-dektol-d-72|Dektol (D-72)]] — paper-developer cousin (same MQ family but with carbonate accelerator and added Hydroquinone for high contrast)