Development time

Ilford FP4 Plus in 510-Pyro

20:25 at 20°C, 1+100 dilution, box speed.

Start timer · 20:25

Time

20:25

Stand

Dilution

1+100

Temperature

20°C

Box speed

ISO 125

B&W

All 2 times

Dilution	EI	Time	Temp	Agitation	Timer
1+100	125	20:25	20°C / 68°F	Stand	Start timer
1+100	125	8:30	21°C / 70°F	Continuous	Start timer

EI is the speed the film was rated at when shooting. Times marked “not yet verified” come from secondary sources and haven’t been checked against a manufacturer datasheet.

Other temperatures

18°C	19°C	20°C	21°C	22°C	23°C	24°C
25:31	22:52	20:25	18:23	16:20	14:42	13:16

Calculated from the 20°C time using Ilford’s temperature compensation factors, not taken from a datasheet. Most B&W developers behave well between 18°C and 24°C.

Mixing

Dilution	300 ml (one 35mm roll)	500 ml (one 120 roll)
1+100	3 ml developer + 297 ml water	5 ml developer + 495 ml water

How they work together

510-Pyro: Very-high acutance, full film speed, compensating contrast. Exceptional highlight control with subtle staining.
Ilford FP4 Plus: Often considered a benchmark for medium speed B&W. Notable sharpness and fine grain. Well-suited for high-quality enlargements.
Notes on this pairing: Hartung semi-stand: 1 min continuous inversion, then one inversion at 10, 20, 30 min.
Rotary processor or tray, continuous agitation.

FP4 Plus in other developers

Diafine