FX-39

FX-39 is Geoffrey Crawley's fine-grain phenidone-hydroquinone film developer, originally published in the British Journal of Photography in 1974 as the latest in Crawley's "FX" series of analytical alternatives to commercial developers. FX-39 was designed as an updated alternative to D-76 with claimed finer grain and better acutance through optimized phenidone:hydroquinone ratios and a milder buffering system. It is a PQ-class developer in the same chemistry family as Microphen, Ilford DD-X, and Kodak XTOL.^[1]

Paterson Photographic acquired and re-released the formula commercially in the 2000s as Paterson FX-39, then released a revised formulation Paterson FX-39 II around 2010. Most contemporary darkroom workers using "FX-39" today are using FX-39 II from the Paterson liquid concentrate, mixed 1:9 with water for one-shot use.

When to choose FX-39 over alternatives

• Prefer FX-39 when: you want PQ-class fine grain in a liquid concentrate; you're in the UK / Europe where Paterson distribution is strongest; you're comparing against XTOL and want to avoid powder-mixing; you're working with traditional B&W films (HP5+, Tri-X, FP4+) and want better acutance than D-76 1:1.
• Prefer XTOL when you're in the US / Canada (Kodak distribution); you're shooting T-grain emulsions (TMax, Delta) where XTOL was specifically optimized; you don't mind powder-mixing.
• Prefer Microphen when push-processing — Microphen's PQ formulation is calibrated for shadow-density-recovery at +1 to +2 stops while FX-39 is optimized for normal speeds.
• Prefer Perceptol when grain matters more than speed — Perceptol gives the finest grain of the modern fine-grain class but with measurable speed loss.
• Prefer D-76 when working from a published formula or when paper-print contrast considerations argue for the well-known D-76 tonality.

FX-39 vs FX-39 II

The Paterson reformulation around 2010 introduced subtle changes that matter for users moving between the two:

	FX-39 (original Crawley 1974)	FX-39 II (Paterson ~2010)
Mix form	DIY from raw chemicals	Liquid concentrate
Working dilution	1:9 (single dilution recommended)	1:9 standard, 1:14 for finer grain
Active developing agents	Phenidone + glycin + hydroquinone	Phenidone + hydroquinone (no glycin)
Buffer	Borax	Borax + carbonate trace
Times for HP5+	~7–8 min at 20°C	~7 min at 20°C
Notes	Glycin component contributes to slightly warmer tonality	Glycin removed for stability of liquid concentrate; tonality slightly more neutral

The published time tables online (Massive Dev Chart, Ilford technical sheets) refer to FX-39 II in nearly all cases — if you're using a Paterson bottle, you have FX-39 II. The DIY-from-scratch original Crawley formula (with glycin) is now mainly of historical / archive interest.

Phenidone-Hydroquinone (PQ) chemistry

FX-39 is part of the PQ developer family — phenidone as the primary developing agent, hydroquinone as the secondary regenerator. The PQ pairing replaces the older Metol-Hydroquinone (MQ) chemistry of D-76 and gives several advantages: lower toxicity (phenidone is much less hazardous than metol), longer working life of stock and working solutions, and finer grain at equivalent contrast.^[1]

In FX-39's specific PQ ratio (~0.12 g phenidone + 0.25 g hydroquinone per litre of stock), the developing agents work in a regenerative cycle: phenidone reduces silver halide directly, hydroquinone regenerates the oxidized phenidone back to its active form. Sodium sulfite serves both as preservative and as a mild silver solvent — at the relatively low ~5 g/L concentration in FX-39, the solvent action is moderate, contributing to FX-39's "fine grain plus good acutance" balance. Higher-sulfite developers (D-76, Microphen) trade some acutance for finer grain; lower-sulfite developers (Beutler) trade fineness for high acutance. FX-39 sits in the middle of this spectrum.

Dilution and time reference

Reference times for FX-39 II at 20°C with continuous-30s-then-10s-every-60s agitation:

Film	ISO	1:9	1:14	1:19
Ilford HP5+	400	8.5 min	12 min	16 min
Kodak Tri-X 400	400	9 min	13 min	17 min
Ilford FP4+	125	6.5 min	9.5 min	13 min
Ilford Delta 100	100	8 min	11 min	14 min
Ilford Delta 400	400	8 min	11 min	14 min
Ilford Delta 3200	3200 (rated 1600)	12 min	—	—
Kodak T-Max 100	100	8.5 min	12 min	15 min
Kodak T-Max 400	400	9 min	13 min	17 min
Foma Fomapan 100	100	5 min	7.5 min	10 min
Foma Fomapan 400	400	6.5 min	9.5 min	13 min
Ilford Pan F+	50	5 min	7 min	9 min

Choosing the dilution. 1:9 is the standard everyday dilution — neutral grain, neutral acutance, predictable times. 1:14 gives moderately finer grain at the cost of a longer development time. 1:19 (and beyond, 1:24, 1:29) is "stand-development territory" — substantial acutance lift, finer grain, but unpredictable behaviour with very long times; reserve for experimental work or specific aesthetic goals.

Practical notes

• FX-39 is the British alternative to American XTOL — same general chemistry family, similar fine-grain claims, different supply chain. Choose by local availability rather than expecting a quality difference.
• One-shot use only. The 1:9 working solution is exhausted after a single tank's worth of film; discard after use. Do not attempt to reuse working dilution.
• Concentrate shelf life: liquid concentrate keeps 1+ year sealed in original Paterson bottle; opened concentrate keeps 6 months.
• Mixing from raw chemicals (original FX-39): dissolve in order listed at 40°C with continuous stirring; the glycin component takes longest to dissolve. Cool to 20°C before use.
• Modern reformulation choice: Paterson FX-39 II is the practical default. The original Crawley formula with glycin is mainly of archive / historical interest now.
• PPE: nitrile gloves and eye protection during mixing of raw chemicals; standard darkroom hygiene during use of the diluted concentrate.
• Cross-contamination: keep separate from fixer trays — common rule for any developer.

Related recipes

• XTOL — Kodak's modern PQ-ascorbate fine-grain alternative; powder-mixed; stronger US distribution.
• D-76 — the MQ-buffered comparison standard against which FX-39 was originally benchmarked.
• Microphen — Ilford PQ alternative optimized for push processing.
• Perceptol — ultra-fine-grain Ilford developer; trades speed for grain.
• HC-110 — Kodak liquid concentrate alternative; different chemistry (not PQ) but similar one-shot workflow.