Diafine

Diafine is the canonical two-bath film developer — currently sold by Acufine Inc in the United States (the brand has changed hands several times since its mid-20th-century introduction; some European markets still see Tetenal-branded Diafine). It is the simplest "set and forget" workflow in B&W development: 3 minutes in Bath A, 3 minutes in Bath B, and you're done — fixed across virtually all films, no temperature compensation needed, no agitation calibration, no per-film time adjustment.^[1]

The two-bath structure is what makes Diafine distinctive. Standard one-bath developers (D-76, HC-110, Microphen, etc.) combine the developing agents and the alkali activator in a single working solution — development proceeds throughout the immersion time, and timing precision matters. Diafine separates these:

• Bath A contains the developing agents (Phenidone + Hydroquinone) in a mild buffer with no alkali — film is loaded with developer over 3 minutes but no significant development happens
• Bath B contains the alkali activator (sodium carbonate or similar) plus restrainer — when the film transfers to Bath B, the developing agents already in the emulsion become active and develop the image

The development is self-limiting: the only developing agents that can produce density are those carried over from Bath A in the emulsion. Once the carry-over is exhausted, no further development happens — extending Bath B time has minimal effect. This is the mechanism that makes Diafine times "fixed" across films and conditions.^[2]

The trade-off: Diafine produces a specific look that's neither neutral D-76 nor punchy HC-110 — moderately compressed highlights, slightly enhanced shadow detail (the speed-increase effect), distinctive grain character. Photographers either love it or find it limiting; there's not much middle ground. It's also a speed-increasing developer — Tri-X 400 rates at EI 800-1600 in Diafine, HP5 Plus at EI 800-1250. The EI bump comes "free" without push-processing time adjustments, but only at Diafine's specific tonal character.

Diafine is supplied as a two-part powder set (one for Bath A, one for Bath B), each mixing to one quart (~950 ml) of working solution. Both baths are reusable for years and many rolls.

When to choose Diafine over HC-110 or Microphen

Diafine sits in the "occasional shooter / simple workflow" niche along with HC-110 and to a lesser extent Microphen:

• vs HC-110: HC-110 has the multi-dilution flexibility and very long concentrate shelf life; Diafine has the simpler workflow (no dilution math, fixed times across films) and even longer working-solution life (years vs HC-110's working-solution one-shot use). Choose HC-110 when dilution flexibility matters; Diafine when simplicity matters.
• vs Microphen: Microphen is the routine speed-increase developer; Diafine is the speed-increasing two-bath alternative. Microphen times vary by film and EI; Diafine times are fixed. Choose Microphen for predictable per-film control; Diafine for "I just want to develop this roll without thinking."
• vs D-76: D-76 is the routine workhorse; Diafine is the routine simplification. Choose D-76 for batch-to-batch grain consistency; Diafine for reduced cognitive load.
• vs Pyrocat-HD two-bath: Pyrocat can be used in a two-bath configuration similar to Diafine, with stain benefits. Choose Pyrocat two-bath when you want stain + two-bath workflow; Diafine when you don't want stain to complicate scanning.

The two-bath PQ chemistry — self-limiting development

Diafine's chemistry is structured around the separation of developing agent loading from development activation:^[2]

Bath A contains:

• Phenidone (primary developing agent at low concentration — same as Microphen's PQ chemistry)
• Hydroquinone (regenerating partner)
• Sodium sulfite (preservative; provides mild buffering but not alkaline)

In Bath A, the film soaks for 3 minutes — during this time, Phenidone and Hydroquinone diffuse into the emulsion but do not develop because the bath lacks the alkaline pH that activates them. Effectively, Bath A is a "loading bath" — getting developing agents into the emulsion in proportion to the silver halide structure.

Bath B contains:

• Sodium carbonate (alkali activator — raises pH to ~10)
• Sodium bromide (restrainer to control fog)
• Sodium sulfite (preservative)

When the film transfers to Bath B (no rinsing between baths), the developing agents already in the emulsion become active. Development proceeds rapidly — but only as long as developer remains in the emulsion. After ~30-60 seconds of active development, the carry-over developer is exhausted and no further density builds. The full 3-minute Bath B time provides comfortable margin but no precision is required.

The speed-increase effect comes from this mechanism: because development is "fed" by the carry-over from Bath A, and Bath A loads more developer where there's more silver halide (i.e., the highlights), the highlights develop more aggressively than the shadows in proportional terms. The result: shadows develop fully at lower density, highlights develop with controlled compression — equivalent to a +1 to +2 stop push at standard one-bath times, without the visible push-grain effects.

Fixed times across films and conditions

The signature operational property: 3 minutes A + 3 minutes B at any temperature 20-30°C. Specifically:

Film	Box ISO	EI in Diafine
Kodak Tri-X 400	400	800-1250
Ilford HP5 Plus	400	800-1000
Kodak T-Max 400	400	800-1000
Ilford Delta 400	400	800-1000
Kodak T-Max 100	100	200-320
Ilford FP4 Plus	125	200-320
Ilford Delta 100	100	200-320
Kodak Tri-X 320 (sheet)	320	640-1000

Procedure: Pour Bath A, agitate continuously for first 30 seconds, then 5-second inversion every 30 seconds for 3 minutes. Drain Bath A back into its bottle (reuse). Pour Bath B without rinsing the tank, agitate continuously for first 30 seconds, then 5-second inversion every 30 seconds for 3 minutes. Drain Bath B back into its bottle. Stop bath / fix as normal.

Practical notes

• Reuse both baths for many rolls — Diafine is famously reusable. Manufacturer rates 16 rolls per quart of A+B at fresh strength; many photographers report 30+ rolls with no visible degradation. Watch for Bath A clear-yellow → amber-brown shift (oxidation) or Bath B darkening as exhaustion signals.
• Both baths keep multi-year shelf life in tightly-sealed full bottles. The most-cited product feature.
• Don't rinse between Bath A and Bath B — the carry-over is the entire mechanism. Rinsing destroys the two-bath workflow and reverts to standard one-bath D-76-equivalent behavior.
• Temperature: 20-30°C works. Diafine is genuinely temperature-tolerant — winter darkroom at 18°C works (slightly less speed effect); summer darkroom at 27°C works (slightly more density).
• Don't push films further — Diafine's effective EI is the published EI; pushing beyond that produces blocked highlights without shadow recovery.
• PPE: Standard developer-handling — nitrile gloves and eye protection. The high-pH Bath B is more skin-irritating than Bath A.

Related recipes

• [[recipe-microphen|Microphen]] — single-bath PQ alternative with comparable speed-increase effect; more flexible per-film control but more complex workflow
• [[recipe-hc-110|HC-110]] — concentrate alternative for simple-workflow photographers who want dilution flexibility
• [[recipe-d-23|D-23]] — DIY two-bath alternative when you control bath times and Bath B alkali (D-23 + Kodalk two-bath workflow)
• [[recipe-d-76|D-76]] — single-bath MQ workhorse; the comparison standard
• [[recipe-pyrocat-hd|Pyrocat-HD]] — staining alternative that can also be configured as two-bath