Lab: Processing Your First Film

The camera you commissioned on the previous page will expose a sheet of film as readily as a sheet of paper, and every later part of this course that measures a negative assumes you have processed one. This is that procedure, done once, properly, with the numbers taken from the makers’ own sheets.

Purpose

To take one exposed film — a 4 × 5 inch sheet from the pinhole camera, or a roll of 35 mm or 120 if that is what you have — from the dark to a dry, readable negative, and to write down enough about how you did it that you could do it again identically next month.

!A recipe you run now and understand later

This page is deliberately a procedure and not an explanation. You are going to follow five steps whose chemistry you have not been taught yet, and that is the right order: the rest of the course is easier to learn once you have watched an image appear on a piece of film you exposed yourself.

Every step names the part that owns it, and none of that chemistry is pre-empted here.

Step on this page	What it does, in one line	The part that explains it
Mixing from stock	Turns a concentrate into a working solution of known strength	Part II, already learned: concentration and dilution
Develop	Amplifies the invisible latent image about a hundred-million-fold	Part IV for the amplification; Part VIII for the developing agents, the alkali, the preservative and the restrainer that make a formula
Agitate to a scheme	Replaces exhausted developer at the emulsion surface	Part III for diffusion; Part IX and Part XXVII vary the scheme deliberately as an experiment
Stop	Halts development at a known instant instead of letting it trail off	Part X
Fix	Dissolves the silver halide that was never exposed, so the film can go into the light	Part XI, including clearing time and capacity
Wash and dry	Removes the fixer and its by-products so the image lasts	Part XII, including permanence and silver recovery
Read the negative	Turns “it looks about right” into a number	Part XIII for the curve; Part XV for the densitometer that measures it
When it goes wrong	Names the fault from the evidence	Part XXVIII, Failure Analysis

If you want the why before the how, read Part IV’s development lesson first. It is enough. Everything else can wait.

Every time, temperature and dilution on this page comes from a manufacturer’s published instruction, and is cited to it. Where the course could not find a published figure — and there are three such gaps, all flagged where they occur — it says so and sends you to the sheet that came with your own materials rather than inventing a number. That is not caution for its own sake: a development time is a property of one film in one developer at one temperature with one agitation scheme, and a number carried across from a different combination is not an approximation, it is a different experiment.

Learning objectives

By the end you will be able to:

• Load film into a tank, a sheet-film holder or a tray in total darkness, having practised in the light first, and identify the emulsion side by the notch.
• Mix a working solution from a concentrate using C₁V₁ = C₂V₂ and the tank’s real volume.
• Find your film and developer in a published time-temperature table, read the time at the temperature you can actually hold, and use the maker’s own compensation chart rather than a rule of thumb.
• Hold four baths within the range the maker specifies, and say what drifting outside it does.
• Follow a published agitation scheme exactly and explain why an unspecified scheme gives an unrepeatable result.
• Measure a fixer’s clearing time and use it both to set the fixing time and to decide when the bath is finished.
• Run the published wash sequence and dry a film without marks.
• Read a dry negative against a step wedge and describe it in four words that are not interchangeable: thin, dense, flat, contrasty.
• Write a lab-notebook entry a stranger could repeat.

Prerequisites

Commissioning the pinhole camera, because the film you are about to process should be one you exposed and logged; the latent image made visible, which is where you first developed anything; concentration and dilution, which owns the arithmetic below; laboratory safety and PPE; and chemical waste and silver waste, which owns the container the used fixer goes into.

Safety classification

Level A. The criteria that decided it:

• Substances. Three proprietary photographic solutions at their makers’ own working dilutions, plus a non-ionic wetting agent at 1+200, in volumes of one litre or less. Nothing is mixed from powder on this page, nothing is concentrated, nothing is heated beyond a warm water bath at 20 to 25 °C.
• Energies. None. A water bath at room temperature and a hand-held tank.
• Procedures. Pouring dilute solutions into and out of a sealed tank, or rocking a tray. The failure mode is a spoiled film.
• Waste. Used fixer is silver-bearing and is collected.
• Darkness. The one genuinely unusual condition, and the controls for it are procedural: the bench is laid out and the room cleared before the light goes off, and nothing hot, sharp or breakable is on it.

What is not a hazard here, and why. Nothing on this page produces a vapour, a gas, an aerosol or a dust. The developer arrives as a liquid concentrate and is diluted with water; the stop is citric rather than acetic, and its maker describes it as low odour; the fixer is a cold aqueous solution; and the tank is closed while it is agitated, so nothing is thrown into the air. That is why the ventilation control below is ordinary room ventilation and not extraction. The silver, likewise, is not mobile until the fixer makes it so. In the film it is an insoluble halide bound in hardened gelatin; in the fixer it is a dissolved complex, and that single change of state is the entire reason one of the four baths is collected and three are not.

Two things that are worth naming because they catch people. Working in the dark is where hands meet edges and elbows meet full graduates. And a skin sensitiser is a cumulative hazard: the risk from one film is negligible and the risk from four hundred films with bare hands is a career-ending dermatitis, which is why the glove instruction is not proportionate to today’s exposure.

Hazards

Developer. Photographic developing agents include known skin sensitisers, and the working solution is alkaline. Hydroquinone’s aggregated GHS classification includes skin sensitisation and serious eye damage; p-aminophenol and ascorbate developers carry their own statements. This course has not obtained the current safety data sheet for each named proprietary product, and quotes no hazard statements for them; read the SDS for the bottle in your hand, which the maker publishes and which carries a version and a date. ILFORD’s own general instruction is that gloves, eye protection and an apron or overall are worn when handling and mixing all their chemicals.

Stop bath. A dilute organic acid at 1+19. An irritant, and an eye irritant in particular.

Fixer. An ammonium thiosulfate solution at 1+4. An irritant; its real problem is what it contains after use.

Wetting agent. A non-ionic surfactant at 1+200. Its practical hazard is that it makes a wet floor slippery in a way plain water does not.

Cross-contamination. ILFORD warn that even a trace of fixer can contaminate the developer and possibly ruin the next film, and their beginners’ sheet recommends different-coloured beakers so that one solution is never poured into another’s vessel. Treat that as a rule and not a suggestion: the mistake happens in the dark, in a hurry, and it is invisible until the film comes out.

Working in total darkness. Trip hazards, spills and cut fingers. Lay the room out with the lights on, do not change it in the dark, and know where the light switch is.

Required PPE

• Nitrile gloves whenever a solution is being mixed or poured. HSE’s COSHH essentials sheet for manual film and plate development takes single-use nitrile as splash protection where the SDS gives nothing more specific.
• Eye protection from before the first cap comes off.
• An apron or overall.
• Dedicated utensils, never shared with anything used for food preparation, and stored apart from it. ILFORD state this directly, as does HSE’s general COSHH guidance.

Ventilation

The control here is ordinary room ventilation: an openable window or an extractor, and not a sealed cupboard. Extraction is not among the controls on this page, because none of the four baths generates a vapour that would need it — the solutions are cold, dilute and aqueous, the stop is citric rather than acetic, and the tank is closed during agitation. What air movement is actually for is that a person shut in a small unventilated room with four trays for two hours stops concentrating, and this procedure is a sequence of timed steps that does not tolerate a lapse of attention.

Materials

Item	Quantity	Notes
The exposed film	1 sheet or 1 roll	With its exposure-log row already written.
A scrap of the same unexposed film	a corner, or a 35 mm leader	For the clearing-time test. Cut it in the dark from the same box.
A second sheet of the same film, unexposed	1	The control, for the light-tightness re-test in the preparation stage.
Negative sleeves or a folder	—	Cellulose triacetate, polyester or a pH-neutral paper; ILFORD name all three for storage.
Pencil, and a printed lab-notebook page	—
A step wedge, or a strip of your own film given a stepped exposure	1	See the reading section.

Chemicals

Chemical	Quantity	Form
Film developer concentrate	60–120 mL	Diluted to the maker’s ratio for the film in the tank. The worked example uses ILFOTEC DD-X at 1+4, which ILFORD specify for one-shot use.
Stop bath concentrate	15–30 mL	Diluted 1+19. ILFOSTOP is a citric acid stop bath with an indicator dye.
Rapid fixer concentrate	60–120 mL	Diluted 1+4; ILFORD state that for all film fixing applications their rapid fixer is diluted 1+4, where for RC paper 1+9 is also offered. It is an ammonium thiosulfate fixer.
Wetting agent	2–3 mL	At 1+200: 5 mL per litre of final rinse water.
Water	about 10 L	Dilution and washing.

A note on which developer. The worked example uses a liquid concentrate because it needs no weighing and no dissolving, and because ILFORD publish a complete beginner’s procedure for it. Powder developers such as ID-11 or D-76 are cheaper per film and are what Part VIII will have you mix from raw chemicals; a powder is dissolved to a stock solution first and then diluted, which is one more step and one more thing to get wrong on a first film.

Equipment

A developing tank with the spiral or sheet-film holders for your format; a changing bag or a room that can be made dark; three or four graduates, one per solution and never swapped, ideally in different colours; a mixing jug; a thermometer reading to 0.5 °C; a timer; a washing-up bowl to serve as a water bath; film clips, one plain and one weighted; a squeegee or a clean chamois; scissors; a light box or a bright window; and a loupe.

Estimated cost

Cost band ££, and it is the tank that puts it there. A developing tank with reels, or a tank with sheet-film holders, is the one substantial purchase in this part; a changing bag, a thermometer and a set of graduates are modest; the three chemistry concentrates will each process many films. Dated UK prices live in the laboratory planner rather than in this text.

Estimated consumables cost

The tank is what puts the band above at ££ and the tank is equipment. Per film, this session consumes one roll, four solutions and a sleeve — and the three concentrates will each do many more films.

Consumed	This session	Sourced price	Cost this session
Black-and-white film, 35 mm	1 roll, plus a scrap for the clearing test	£6.37–£11.40 per one 35 mm roll, 36 exposures	£6.37–£11.40
Film developer concentrate	60–120 mL at 1+4, one-shot	£33.28–£41.08 per 1 L of liquid concentrate, diluted 1+4 one-shot	£3.00–£3.70
Stop bath concentrate	15–30 mL, diluted 1+19	£10.66–£12.18 per 500 ml of citric acid concentrate, diluted 1+19	£0.47–£0.54
Rapid fixer concentrate	60–120 mL, diluted 1+4	£21.05–£25.98 per 1 L of ammonium thiosulfate concentrate, diluted 1+4 for film	£1.89–£2.34
Wetting agent	2–3 mL at 1+200	£28.70 per 1 L of concentrate, diluted 1+200	£0.07
Negative sleeves	one strip-sleeve page	None. A named price gap: sleeving that passes the Photographic Activity Test	—
Water	about 10 L	Metered supply; the planner prices no water	—

The priced rows come to £11.80 to £18.04 for one run of this session, at the retail ranges read on 5 September 2026 and recorded in the laboratory planner. That is a floor, not a total: 1 of the 7 rows carries no dated price, so it is counted as nothing here and is certainly not free. A priced entry is a dated range to plan against, never a quotation.

The developer is priced at the mid-point of the 60–120 mL range the page gives, because it is used one-shot and thrown away; the stop and the fixer are re-used within a session and the figures below are for one film’s worth of concentrate. Sleeving that passes the Photographic Activity Test is a named price gap, which is worth knowing before you buy the cheap sleeves.

Waste streams

Used fixer is the stream that is collected, into the labelled silver-bearing container Part II established, together with the first change of wash water. ILFORD note that a film fixing bath can tolerate 8 to 10 g of silver per litre before it misbehaves, which is a measure of how much silver a working bath accumulates and therefore of why it must not be discharged.

Used developer and used stop carry no silver. Local regulation governs their disposal and it differs between authorities, even within the United Kingdom. ILFORD’s guidance for UK domestic users is that local authorities usually accept small quantities of chemical waste at Household Waste and Recycling Centres, bottled separately and clearly labelled, and that different wastes should never be combined for disposal; Kodak publish similar environmental guidance for amateurs. Find out what your authority accepts before the session.

Alternative route

No darkroom: a changing bag. Everything up to closing the tank lid happens inside it, and the rest happens in daylight. ILFORD’s own leaflet names the changing bag as the alternative to blacking out a room. Practise with a spoiled film first, because a bag is more awkward than a dark room, not less.

No tank: tray processing, in total darkness, described as route C below. It is how sheet film was processed for a century and it works; it also scratches film and gives uneven density more readily than a tank, which is why the tank is preferred as soon as one can be afforded.

No pinhole camera, or no sheet film: route B, a roll of 35 mm or 120 from any film camera. The two routes rejoin at “start development” and everything after that is identical.

No running water: the ten changes of standing water that ILFORD publish as an alternative to a running wash, each lasting one minute, or the five-ten-twenty inversion sequence given for spiral tanks.

The five baths, drawn to scale, with the part that owns each

DELTA 100 in DD-X 1+4, 35 mm tank

Develop 12 min — Parts IV and VIIIStop 10 s — XFix 3 min — XIWash 5-10 min — XIIRinse + dry

FOMAPAN 100 in ID-11 stock, 4 x 5 sheet

Develop 6-7 minRinse 10 sFix 3-10 minWash 15 min above 15 °CRinse + dry

010 min20 min30 min

Two published sequences to the same scale. Development is the only step whose length is critical to a fraction of a minute; the stop is the shortest and the wash the longest, and both are specified by their makers rather than judged. Every block is a manufacturer's own figure for that film or that chemical.

Preparation

1. Re-test the camera with a film holder in it

The commissioning page proved the camera light-tight with the paper back on. A sheet-film holder is a different back and a different set of joints: the design lesson has the holder sealing itself on its own light-trap ridge while the camera’s spring frame only holds it square. That is a different seal, so it needs its own test, and film is not the material to discover a leak on.

Load an unexposed sheet into a holder, fit the holder, withdraw the dark slide, keep the shutter closed, and stand the camera in full sun for thirty minutes exactly as on the commissioning page. Process it with everything else, alongside a second unexposed sheet that never left the box. If the two match, the film back passes.

While the holder is in the camera, measure the film-plane distance if you have not already: push a rod or a strip of stiff card through the pinhole until it touches the septum where the film will lie, mark it flush with the outer face of the pinhole plate, withdraw and read, then subtract the plate thickness. The course gives no figure for this, because it has not obtained a manufacturer’s drawing or a published standard for the 4 × 5 inch holder pattern; yours is the only number that is true of your camera.

2. Practise loading in the light

ILFORD’s instruction is explicit and it is the single best predictor of whether a first film survives: practise threading the spiral in daylight with a spoiled film until it goes easily, then with your eyes closed, and only then in the dark with the real one. They add the detail that matters most and is easiest to overlook: the spiral must be completely dry. A reel that feels dry and is not will jam half way, in the dark, with the film already out of its cassette.

For sheet film, do the same with a spare sheet and the holder: find the notch, seat the sheet under both rails, and close the slide, twice, with your eyes shut.

3. Lay the bench out and mix the solutions

Set out, left to right and in the order you will use them, everything you will touch in the dark, and do not move anything afterwards. Then mix.

🧮C₁V₁ = C₂V₂, applied to a dilution written as 1+n

A dilution written 1+n means one part concentrate to n parts water, so the working solution is one part in (n+1). Treating the concentrate as 100 per cent:

C₁V₁ = C₂V₂, with C₂ = C₁/(n+1), so V₁ = V₂/(n+1)

Dilution to a fixed final volume

V₂ is the volume the tank needs, V₁ the volume of concentrate, and the water is the difference.

ILFORD’s own worked example, from the beginners’ leaflet, for one 35 mm film: 60 mL of ILFOTEC DD-X into 240 mL of water gives 300 mL at 1+4. Check it: 300/(4+1) = 60. ✓ They mix the stop the same way, 15 mL of ILFOSTOP into 285 mL for 300 mL at 1+19 — 300/20 = 15 ✓ — and the fixer as 60 mL into 240 mL.

Now for your tank. Read the capacity off the tank itself; this course has not obtained a tank manufacturer’s data sheet and quotes no capacity figure, and tanks of the same nominal format differ. Suppose yours takes 600 mL:

Dilution	Concentrate	Water	Check
1+4	120 mL	480 mL	600/5 = 120
1+9	60 mL	540 mL	600/10 = 60
1+19	30 mL	570 mL	600/20 = 30
1+200	3 mL	597 mL	600/201 = 2.99

Two practical cautions from the makers. ILFORD advise against measuring less than 10 mL of DD-X concentrate at a time, because the proportional error in a very small measurement is large — which is Part II’s measurement-uncertainty lesson arriving in a bottle. And for the wetting agent they warn that too much is as bad as too little, both giving uneven drying, so 3 mL means 3 mL and not a splash.

Stand the mixed solutions in a bowl of water a couple of degrees warmer than the working temperature — ILFORD’s own instruction — and let them come to 20 °C together. Measure with the thermometer; do not judge by hand.

4. Find your time in the maker’s table

Look up your film, in your developer, at your dilution, in the sheet published for that film. Some figures, all quoted from their makers’ current sheets, to show what the table looks like:

Film	Developer and dilution	Time at 20 °C	Published where
DELTA 100 Professional (35 mm)	ILFOTEC DD-X 1+4	12 min	ILFORD’s beginners’ leaflet
FP4 Plus (35 mm and roll)	ILFOTEC DD-X 1+4 at EI 125	10 min	FP4 Plus sheet
FP4 Plus (35 mm and roll)	ID-11 stock at EI 125	8½ min	FP4 Plus sheet
HP5 Plus (35 mm and roll)	ID-11 stock at EI 400	7½ min	HP5 Plus sheet
FOMAPAN 100 Classic (all formats)	ID-11 or D-76 stock	6–7 min	FOMAPAN 100 sheet

📓A gap in the published data, and what to do about it

Read the headings on those tables. ILFORD’s development-time tables for FP4 Plus and HP5 Plus are headed “35mm and Roll Film”, and ILFORD publish no separate sheet-film development time for either. What they do publish for sheet film is the agitation instruction — continuous agitation by rocking the dish or tray — together with the general note that where continuous agitation is used, the tabulated times should be reduced by up to 15 per cent.

So a tray-processed 4 × 5 sheet of FP4 Plus in ID-11 stock works out at about 7¼ minutes — the tabulated 8½ less 15 per cent — and you should record it as the course’s arithmetic on ILFORD’s stated reduction, not as a figure ILFORD printed. FOMA are different in a way worth reading carefully: their FOMAPAN 100 sheet gives one development table with no format qualification on it at all, and lists 4 × 5 inch among the sheet-film sizes the film is sold in, so the 6-to-7-minute figure for ID-11 or D-76 stock is not excluded for a sheet — but the table is stated to be for a spiral developing tank with FOMA’s own agitation, and FOMA give no tray instruction anywhere. So there is no maker’s tray time for a FOMAPAN sheet, and no maker’s statement that the tank time covers sheet film either.

Neither gap is a reason to guess. It is a reason to write in the notebook exactly which number you used and where it came from, so that when the negative is thin you can tell a wrong time from a wrong exposure.

Procedure

Three loading routes, then one common sequence.

Loading in the dark: the notch, the emulsion, and the two containers

1. 1Find the notch — FOMA state the notch is at the right upper corner of the short side; with the notch at the top right, the emulsion faces you. Confirm against the diagram on your own box
2. 2Sheet into the holder — under both rails, emulsion outwards; dark slide home with its unexposed face showing
3. 3Roll onto the reel — lugs towards you, 5 cm into the first channel, then rotate the halves back and forth; the reel must be bone dry

One decision governs everything else in the dark: which side is the emulsion. On sheet film it is a notch you can feel; on roll film it is the curl, because the emulsion is always on the inside of the curve.

Route A — Sheet film into a tank’s holders, in total darkness

1. Lights off. Wait until your eyes have adjusted enough to be sure the room is dark; ILFORD’s test for a room is five minutes in it.
2. Open the film box. Take one sheet, find the notch, and check its position: FOMA state that the notch is at the right upper corner of the short side of the format, so with the notch at the top right the emulsion faces you. Confirm this against the diagram on your own box before the session — ILFORD and Kodak both state the emulsion orientation with a figure, and this course read their sheets as text and could not see it, so it does not claim the convention is universal.
3. Slide the sheet into its holder in the tank, emulsion facing the way the holder’s instructions require, and check it is seated at both edges.
4. Cut a small corner off a second, unexposed sheet and put it in a light-tight pot; that is the clearing-time coupon.
5. Close the tank, fit the lid, and only then turn on the light.

Route B — 35 mm or 120 onto a reel, in total darkness

Follow ILFORD’s own step-by-step, which this page does not improve on. For 35 mm: lever the cap off the cassette, slide the spool part way out and slot the leader through the light trap so that the film does not fall on the floor; pull the leader clear of the cassette lips and cut it off square; find the two projecting lugs on the spiral, line them up towards you, push about 5 cm of film into the first channel between them, then rotate the two halves of the reel back and forth to wind the film in; cut the film from the spool at the end and give a few extra turns; put the spiral in the tank, fit the sealing ring and the lid, and put the light on.

For 120 there is no cassette: peel the backing paper away from the film and start the film alone into the reel.

Route C — Tray processing, in total darkness, when there is no tank

The old method, and the one that needs the most practice.

1. Four trays, laid out and filled before the light goes off: developer, stop, fixer, wash.
2. Work a small batch — four sheets at most for a first attempt, one if you can afford the time.
3. Continuous agitation, which for a tray means shuffling: take the bottom sheet, lift it, and lay it on top, over and over, so that every sheet spends the same time face down and face up. Kodak’s instruction for tray processing of sheets is continuous agitation, with the sheets rotated 90 degrees as they are interleaved, and they add that pre-wetting sheet film may improve tray uniformity. ILFORD, by contrast, state that a pre-rinse is not recommended for their films because it can lead to uneven processing. The two makers disagree, for their own products, and you follow the one whose film is in your hand.
4. Reduce the time. Continuous agitation develops faster than the intermittent scheme the tables assume; ILFORD’s instruction is to reduce by up to 15 per cent.
5. Expect scratches on a first attempt. Emulsion is soft when wet, fingernails are hard, and four sheets sliding over one another is four chances per shuffle.

The common sequence

Step 1 — Bring everything to temperature. All four solutions, and the wash water, at 20 °C, or at whatever temperature you have chosen and can hold. ILFORD’s rule is that development temperature is controlled tightly and the later baths should be within 5 °C of the developer; their fixer sheet repeats it, and their beginners’ leaflet puts a preferred band of 15 to 25 °C on the stop.

!Why all four baths, what drift does, and the one claim this page will not repeat

The developer’s temperature is the one that changes the picture. Development is a chemical reaction and its rate rises with temperature, as Part III establishes; the compensation chart above puts a number on it, and the number is steep — three degrees is worth about a quarter of the development time. A developer two degrees warm and a correctly timed clock give an over-developed, contrasty negative, and nothing in the wash will take it back off.

The other three baths matter for a different reason, and the makers give a rule rather than a mechanism. ILFORD’s instruction, repeated on the beginners’ leaflet, on the fixer sheet and on each film’s own sheet, is that all process solutions be kept at the same temperature or at least within 5 °C of the developer. Each bath also has its own published working range — ILFOSTOP 18 to 24 °C, ILFORD RAPID FIXER 18 to 40 °C, FOMA’s fixing 18 to 25 °C — and outside those ranges the published times are not doing what they say. The wash water counts as a bath: ILFORD specify it within 5 °C of the process temperature too.

And then there is reticulation, which this page will not overstate. Reticulation is a network of cracks in the emulsion, produced when swollen gelatin is shocked by a large change of temperature or pH and contracts faster than the layer can accommodate. It is a mechanical failure of the gelatin and it is unmistakable under magnification once you have seen it.

What this course cannot tell you is the temperature gap at which a modern film reticulates, because no manufacturer sheet it has read warns that a home darkroom’s temperature differences will do it, and none gives a threshold. What the makers publish is the 5 °C rule, with no failure mode attached to breaking it. Modern films are hardened during manufacture, and the honest position is therefore this: follow the 5 °C rule because it is published and because the reaction rates alone justify it, not because of a folk warning about cracked emulsion. Clumped grain from a badly chosen developer is misdiagnosed as reticulation far more often than reticulation actually occurs, and Part XXVIII owns telling the two apart. If you want the answer, the experiment is cheap and it is yours to run: two identical films, one processed with all four baths matched and one with a deliberately large gap between them, and a loupe.

Step 2 — Start development. Pour the developer in smoothly but as quickly as you can and start the clock as you finish pouring.

Step 3 — Agitate to the published scheme, exactly. For a spiral tank, ILFORD’s scheme is: four inversions during the first ten seconds, then four inversions again during the first ten seconds of every further minute, tapping the tank on the bench after each set to dislodge air bubbles. FOMA’s scheme for their films is different — continuous agitation for the first 30 seconds, then during the first 10 seconds of every minute — and their table was drawn up with that scheme. Use the one that belongs to the film in the tank, and write down which.

The agitation scheme against the development clock

1. 1ILFORD, spiral tank — four inversions in the first 10 s, then four inversions in the first 10 s of every further minute; tap the tank after each set
2. 2FOMA, their own films — continuous for the first 30 s, then the first 10 s of every minute — a different scheme, matched to a different table
3. 3Pour out — begin pouring 15 seconds before the nominal time, so the clock reaches the mark as the tank empties

Agitation is a variable of the same standing as time and temperature. An unrecorded scheme makes the other two unrepeatable, which is why the makers specify it and why Parts IX and XXVII can vary it deliberately.

Step 4 — End development at the right instant. ILFORD’s own detail: start pouring the developer out fifteen seconds before the nominal time, so that the timer reaches the mark as the tank finishes emptying. Development does not stop when you decide it has; it stops when the developer leaves.

Step 5 — Stop. Pour in the stop bath, invert the tank twice, and after ten seconds pour it out. ILFORD’s published time is 10 seconds at 1+19 in the range 18–24 °C, and they add that the time is a minimum rather than a target.

Step 6 — Measure the clearing time, then fix. Do the clearing test before you fix if you can, or in parallel; it takes a minute and it is the only honest way to know how long to fix.

The clearing-time test, in three stages, and what it decides

1. 1The reference spot — one drop of working fixer on the emulsion, left 30-60 s, gives a clear spot to compare against
2. 2Immerse and time — drop the scrap into the bath and start the clock; the milk fades from the whole piece
3. 3Clearing time — stop when the whole piece matches the spot — fix for twice this; discard the bath when it exceeds twice the fresh-bath time

Clearing is not the end of fixing: the silver-thiosulfate complexes still have to diffuse out of the gelatin, which is why the published rule is twice the clearing time and not one times it.

ILFORD’s method, in their words and in this order: put a drop of working-strength fixer on a small part of the emulsion side of a scrap of unprocessed film and leave it until the emulsion under the drop is a clear spot, which should take about 30 to 60 seconds; immerse the piece in the fixer bath and time how long the rest takes to match that spot; fix for twice that time; and discard the bath once the clearing time in the used fixer exceeds twice the clearing time in fresh fixer. As a cross-check, their published fixing time for general-purpose film at 1+4 is 2 to 5 minutes, so a clearing time that gives an answer outside that band is telling you something about the bath.

Agitate during fixing the same way you agitated during development. Then pour the fixer into its storage bottle, because unlike the developer it is used again — and note on the bottle how many films it has now done.

Step 7 — Wash. ILFORD publish two routes for a spiral tank and both are complete specifications rather than “run some water through it”:

• Running water, 5 to 10 minutes, at a temperature within 5 °C of the process temperature.
• The inversion sequence, which uses far less water: fill the tank with water at the process temperature, invert five times, drain; refill, invert ten times, drain; refill, invert twenty times, drain.

FOMA’s published wash for their films is different again — running water for 15 minutes above 15 °C, or 30 minutes below 15 °C — and it belongs to their film, not to ILFORD’s. If a wash aid is used, ILFORD publish a film sequence for their own: a one-minute first wash, 2 to 3 minutes in WASHAID at 1+4, then a five-minute final wash. Why running water alone is not a specification: it names neither a duration, nor a temperature, nor a flow, and all three change the result. Part XII owns the chemistry of what is being removed and how fast.

Step 8 — Final rinse and dry. Add wetting agent to the final rinse water at the published dilution — 5 mL per litre, which is 1+200 — and measure it, because the maker warns that too much and too little both give uneven drying. Lift the film out, attach a clip, run a clean squeegee or chamois down it once, and hang it with a weighted clip at the bottom in still, dust-free air, high enough that the bottom of the film is clear of the floor. A hair dryer on a low setting, kept moving and about 30 cm away, speeds it up; ILFORD publish a cabinet temperature of 30 to 40 °C as the alternative for their films. Sheet film wants a weight too, or it curls as it dries.

Do not touch the emulsion at any point while it is wet. Wet gelatin is swollen and soft, and a fingerprint in it is permanent.

Expected observations

During development you see nothing, because the tank is closed. That is normal and it is why the scheme is followed by the clock rather than by eye.

When the tank is opened after fixing, the film should be clear where it was never exposed — the rebates on a roll, the edges under the holder’s rails on a sheet — and dense where the highlights were. ILFORD describe a correctly exposed and processed negative as having a full range of tones, with some parts almost clear, like the rebates, and other parts so dense that print is only just readable through them. That is a usable standard by eye and it is the one to hold this negative to.

A milky look after fixing means fixing was not finished. Put it back in the fixer; nothing is lost if you catch it before it dries.

As it dries, watch for water running unevenly down the film — the sign that the wetting agent was too weak, too strong, or absent.

What is happening chemically

The short version, with every mechanism pointed forward to the part that owns it.

Development. The exposed crystals carry a few atoms of silver at a trap site, and the developer reduces the whole crystal wherever such a centre exists:

AgBr + e⁻ → Ag + Br⁻

Chemical development, per formula unit: the silver stays as the image, the bromide goes into the solution

The electron comes from the developing agent, which is oxidised in the process. Which agents, in what alkali, with what preservative and what restrainer, and why two agents together beat either alone, is Part VIII.

Why agitation is not stirring. Nothing stirs inside the gelatin. The developer travels into the layer and its products travel out by diffusion, which Part III owns. What agitation does is thin the stagnant boundary layer of liquid clinging to the emulsion surface, where developer has been consumed and bromide has built up. Leave the film still and that layer becomes locally exhausted, and its composition then depends on which way up the film is and where the dense areas are — which is exactly how streaks form below a dense area, as developer products sink. Agitate to a fixed scheme and the surface is renewed at fixed intervals, so the result is repeatable. The scheme is a variable in the same class as time and temperature, which is why the makers specify it and why Part IX and Part XXVII vary it on purpose.

Stopping. Development is an alkaline reaction and its rate depends steeply on pH. A dilute acid bath drops the pH and the reaction essentially ceases; a water rinse only dilutes it, so it slows down over an uncertain time. ILFORD note the second consequence of stopping properly: the acid neutralises carried-over alkaline developer, which protects the fixer’s pH and prolongs its life. Part X.

Fixing. Two thiosulfate ions complex a silver ion and take it into solution, so the unexposed halide leaves the film and only the developed silver remains:

AgBr + 2 S₂O₃²⁻ → [Ag(S₂O₃)₂]³⁻ + Br⁻

Fixing: the bis(thiosulfato) complex, and the reason spent fixer is silver-bearing waste

Clearing marks the point at which the solid halide has gone. The complexes are still inside the gelatin, and they still have to diffuse out, which is why the published rule is to fix for twice the clearing time. Part XI.

Washing. What is being removed is residual thiosulfate and its silver complexes, by diffusion out of a swollen gelatin layer into water. Leave them in and they decompose over years into silver sulfide, which stains and fades the image. Part XII, which also owns the recovery of the silver from the bottle you have just filled.

Data to record

One lab-notebook entry, written as you go, not afterwards.

Field	Example
Date and session	2026-09-04, evening
Film, format, batch or expiry	FOMAPAN 100 Classic, 4 × 5 sheet, exp. 2028-03
Exposure index used	ISO 100, box speed
Developer, dilution, batch	ID-11 stock, mixed 2026-08-30
Volume, and how it was mixed	600 mL; stock as supplied
Temperature at start / end	20.2 °C / 20.0 °C
Time, and where the time came from	6 min 30 s; FOMAPAN 100 sheet, ID-11 stock, 6–7 min at 20 °C
Agitation scheme, named	FOMA: continuous 30 s, then 10 s each minute
Stop: product, dilution, time	ILFOSTOP 1+19, 10 s
Fixer: product, dilution, clearing time, fixing time	RAPID FIXER 1+4; cleared in 50 s; fixed 2 min
Films through this fixer to date	7
Wash: method, temperature, duration	Running, 19 °C, 15 min
Wetting agent and dilution	ILFOTOL 1+200, 3 mL in 600 mL
Drying: where, how long	Bathroom, hung, weighted, 2 h
Result, in the vocabulary below	Slightly thin; good separation in the highlights
One change for next time	Expose half a stop more, hold the time

And close the exposure-log row the commissioning page opened for this sheet: its processing fields and its result. A log entry that stops at the exposure is half an experiment.

Analysis

Reading the dry negative

Put the dry film on a light box, or hold it against a white wall lit by a window, and lay a step wedge beside it.

With a step wedge. Stouffer’s T2115 is 21 steps at a density increment of 0.15 — half a stop per step — running to a maximum density of 3.05, with the target density of each step published. It is a transmission wedge, so it is the right instrument for film. Find which step your densest highlight matches and which your thinnest shadow matches; the number of steps between them is the negative’s range, in half-stops.

Without one, make a substitute: give a strip of the same film a stepped exposure in daylight, process it with the real film, and use it as a ladder calibrated in stops of exposure rather than in density. Less good, free, and it tells you where your own film sits.

Then use the four words, which are not interchangeable. Getting these apart is the whole point of the exercise, and Part XXVIII will assume you have them.

Word	What it describes	Usual cause	What it is not
Thin	All densities too low; the shadows are at or barely above the clear rebate and hold nothing	Under-exposure	Not flat. A thin negative can be perfectly contrasty
Dense	All densities too high; even the shadows are grey and the highlights are hard to see through	Over-exposure, or over-development	Not contrasty
Flat	The difference between highest and lowest is too small; everything sits in a narrow band	Under-development, exhausted developer, or flare at exposure	Not thin. A flat negative can be dense
Contrasty	The difference is too large; highlights block, shadows empty	Over-development, or a very high-contrast subject	Not dense

Four negatives beside a step wedge, and where to look on each

1. 1Correct — shadow a little above the clear rebate, highlight short of the densest step; the whole subject inside the wedge
2. 2Thin — both readings near the clear end; the shadow is indistinguishable from the rebate. Under-exposure
3. 3Dense — both readings near the opaque end; the highlight runs off the top. Over-exposure, or over-development
4. 4Flat — the two readings only a few steps apart, wherever they sit. Under-development, exhausted developer, or flare

Two readings, taken from one comparison: where the pair sits on the wedge is density, and exposure moves it; how far apart the pair is is contrast, and development moves that. Confusing the two is the commonest first-film misdiagnosis.

Density is not contrast. Density is where the whole scale sits; contrast is how far apart its ends are. They have different causes and different remedies, and the commonest failure of a first diagnosis is to give the remedy for one to the other. Exposure moves density; development moves contrast — that is the rule of thumb the sensitometry of Part XIII will make exact.

The temperature you can actually hold

You will not always be able to work at 20 °C, and the correct response is the maker’s chart rather than arithmetic of your own.

ILFORD's published temperature-compensation chart, read off for three development times

• 12 min at 20 °C
• 9 min at 20 °C
• 6 min at 20 °C

Show the numbers behind this plot

Three falling curves of compensated development time against temperature, read directly from ILFORD's published film development time and temperature compensation chart. The top curve is for a film whose recommended time is 12 minutes at 20 degrees C: it reads 14 minutes 45 seconds at 18 degrees, 13 minutes 15 at 19, 12 at 20, 10 minutes 45 at 21, 9 minutes 45 at 22, 8 minutes 15 at 24, 7 minutes 30 at 25 and 6 minutes 30 at 27. The middle curve is for a recommended 9 minutes at 20 degrees: 11 minutes 15 at 18, 10 at 19, 9 at 20, 8 at 21, 7 minutes 15 at 22, 6 minutes 15 at 24, 5 minutes 45 at 25 and 5 minutes at 27. The bottom curve is for a recommended 6 minutes at 20 degrees: 7 minutes 15 at 18, 6 minutes 30 at 19, 6 at 20, 5 minutes 30 at 21, 5 at 22, 4 minutes at 24 and 3 minutes 45 at 25, and the chart prints no value at 27 degrees for this row. A horizontal reference line is drawn at five minutes, because the chart carries a printed warning that development times below five minutes are not recommended owing to the risk of uneven development: the six-minute curve crosses that line between 22 and 24 degrees, so the chart will hand you a number that the same sheet tells you not to use. The chart's own worked example is that eight minutes at 20 degrees becomes five minutes thirty at 24.

Series	Processing temperature, °C	Development time, minutes
12 min at 20 °C	18.00	14.75
12 min at 20 °C	19.00	13.25
12 min at 20 °C	20.00	12.00
12 min at 20 °C	21.00	10.75
12 min at 20 °C	22.00	9.75
12 min at 20 °C	24.00	8.25
12 min at 20 °C	25.00	7.50
12 min at 20 °C	27.00	6.50
9 min at 20 °C	18.00	11.25
9 min at 20 °C	19.00	10.00
9 min at 20 °C	20.00	9.00
9 min at 20 °C	21.00	8.00
9 min at 20 °C	22.00	7.25
9 min at 20 °C	24.00	6.25
9 min at 20 °C	25.00	5.75
9 min at 20 °C	27.00	5.00
6 min at 20 °C	18.00	7.25
6 min at 20 °C	19.00	6.50
6 min at 20 °C	20.00	6.00
6 min at 20 °C	21.00	5.50
6 min at 20 °C	22.00	5.00
6 min at 20 °C	24.00	4.00
6 min at 20 °C	25.00	3.75

Points read from ILFORD's published compensation chart (April 2002), whose times are rounded to the nearest 15 seconds. This is published data, not a drawn shape. Note that the chart covers 18 to 27 °C only, and that it is offered as a guide for all film and developer combinations — where a film's own sheet gives its own compensation graph, as FP4 Plus does, that one belongs to that film and wins.

Three things to take from it. The slope is steep: three degrees is worth about a quarter of the development time, which is why a thermometer beats a guess. The chart stops at 27 °C and starts at 18 °C, so outside that band it offers nothing and neither does this course. And the chart will hand you a number it also tells you not to use — the six-minute row falls below five minutes above about 23 °C, and the same sheet warns that times under five minutes risk uneven development. When that happens, change the dilution or the developer rather than the temperature.

Reconciling with the exposure log

Look at the negative beside the row you wrote before you opened the shutter. If it is thin, was the exposure short, the development short, the developer old, or the temperature low? Each leaves a different trace, and only one of them is visible on the rebate: the rebate and the frame edges were never exposed, so their density is base plus fog and it is independent of the exposure entirely. A thin picture with a normal rebate is an exposure fault. A thin picture and a thin rebate is a processing fault. That single comparison resolves more first-film arguments than any other, and it is free.

Troubleshooting

What you see	Most likely cause	Confirming check	What to do
Film completely clear, no frame numbers or rebate markings	Never exposed, or fixed before development, or the film was fogged blank	Look for edge printing: an ILFORD roll carries frame numbers whatever the exposure	If the edge printing is absent too, the film went into the fixer first
Film uniformly black	Exposed to light before development	Rebates black as well	Check the loading routine and the tank lid
Thin picture, normal rebate density	Under-exposure	The exposure-log row	Give more exposure; the time was fine
Thin picture, thin rebate	Under-development: time short, temperature low, or developer exhausted	Temperature record and the developer’s age	Re-check the table and the thermometer; mix fresh
Milky or cloudy after fixing	Under-fixed	Clearing test on a scrap of the same film	Re-fix in fresh fixer; measure clearing time and double it
Clear streaks running down from dense areas	Insufficient or irregular agitation	Whether the pattern follows the frame’s dense areas	Follow the published scheme exactly; tap the tank
Circular clear spots	Air bubbles held against the emulsion at the start	Position is random rather than image-related	Tap the tank after each set of inversions, as ILFORD instruct
Runs and streaks appearing only after drying	Wetting agent wrong, or the film was wiped with something gritty	Whether the marks follow the direction of drainage	Measure the wetting agent; both too much and too little cause this
Straight scratches along the length	Reel, squeegee or grit	Whether they run in the direction of travel	Check the squeegee; consider hanging without wiping
Sheet film with density along two edges only	Held in the holder rails, so those strips were shielded	It will be perfectly straight and exactly rail-width	Not a fault; that is the rail shadow, and it is your unexposed reference
Uneven density across a tray-processed sheet	Shuffling too slow or too regular	Whether the pattern is a broad gradient	Shuffle faster; rotate the sheets 90 degrees as Kodak instruct

Clean-up

Used developer goes according to local rules. Used stop the same. Used fixer goes into the labelled silver-bearing container, and so does the first change of wash water. Rinse every graduate, the tank, the reel and the thermometer in running water and stand them to dry — the reel especially, because a damp reel is the commonest cause of a jam next time and it takes hours to dry properly.

Wipe the bench, then wash your hands even though you wore gloves.

Storage

Negatives. Sleeved, flat, dark, cool and dry. ILFORD name cellulose triacetate, Mylar, pH 6.5 to 7.5 paper and inert polyester as suitable sleeve materials, and they recommend storing processed negatives at 10 to 20 °C in the dark. Number the sleeve to match the notebook entry and the exposure-log row, on the day, in pencil.

Solutions. The developer in the worked example is a one-shot: ILFORD’s instruction for DD-X at 1+4 is that it is used once and poured away, and they add that working-strength solutions of it should not be kept more than 24 hours. Working-strength stop and fixer are kept and reused, with the fixer’s life judged by the clearing test rather than by the calendar. Date every bottle and write the number of films it has done on the label.

Unexposed film goes back in a cool, dry place in its original packaging, and exposed film is processed as soon as is practical.

Disposal considerations

The one stream that must not be discharged is the spent fixer, because the thiosulfate complex has put the silver into solution and silver is toxic to aquatic life. That is the reaction above, and the reason for the container. Kodak’s environmental guidance for amateur photographers and ILFORD’s own health-and-safety sheet both point domestic users to collection rather than discharge, and Part XII teaches recovering the silver from it rather than merely handing it over.

Developer and stop carry no silver. The developer is alkaline and contains a sensitiser; the stop is a weak organic acid. Both are usually accepted in small domestic quantities at a Household Waste and Recycling Centre, bottled and labelled separately and never mixed together.

Local regulation governs, and it differs between authorities even within the United Kingdom. Check what yours accepts. The sentence is not a formality: an authority that takes photographic waste and one that does not are a mile apart and both exist.

Questions

1. Your developer is supplied as a concentrate to be used at 1+9 and your tank holds 600 mL. State the concentrate and water volumes. Then restate them for 1+4 in the same tank, and say which of the two ILFORD’s minimum-measurement advice would make you more confident about.
2. A fixer cleared a scrap of film in 45 seconds when it was fresh. Two months later the same test on the same film takes 2 minutes 30 seconds. What does that tell you, what should the fixing time now be, and what should you actually do?
3. Your negatives are evenly thin across the whole sheet including the rebate. Distinguish under-exposure, under-development, exhausted developer and a temperature below the table, and say which single piece of evidence separates the first from the other three.
4. Your film’s sheet gives 9 minutes at 20 °C but the room and the water are at 24 °C. What time does ILFORD’s compensation chart give, and what would you have to check before using it?
5. Why does ILFORD tell you to start pouring the developer out fifteen seconds before the nominal development time, and what would you have to change if your tank took forty seconds to empty?
6. You process four sheets in a tray with continuous agitation, using the time from a table drawn up for a spiral tank with intermittent agitation. Which way will the negatives be wrong, by roughly how much, and what does the maker say to do about it?

Further experiments

Process a second film at a different temperature, using the chart. Same film, same developer, same agitation, same exposure, one at 20 °C and one at 24 °C with the compensated time. If the chart is right the two negatives should match. Any difference is the chart’s error on your combination, which is worth knowing before you rely on it in a cold winter darkroom.

Run the clearing test every session for a season and plot it. Clearing time against the number of films the bath has done is an exhaustion curve you measured yourself, and it will tell you your fixer’s real capacity, which is not necessarily the published one.

Process one film with no stop bath, using a water rinse instead. ILFORD state that this increases the risk of processing marks and stains and shortens the fixer’s life; see whether you can find either effect, and record honestly if you cannot. One film proves nothing, which is itself the lesson.

Deliberately break the agitation scheme on a spare film: agitate continuously throughout, and compare with one agitated to the published scheme at the same time and temperature. The continuously agitated film should be denser and more contrasty, and this is the experiment Part IX builds on.

Weigh the wash. Run the inversion sequence with a measuring jug under the tank and record the water used, then do the same for a ten-minute running wash. The ratio is the argument for the sequence, and it is the beginning of Part XII’s water-economy lesson.

Check your understanding

Question 1. Your developer is supplied as a concentrate for use at 1+9, and your tank holds 600 mL. How much concentrate and how much water, and how much concentrate would the same tank need at 1+4?

• 60 mL concentrate and 600 mL water; then 120 mL and 600 mL
• 60 mL concentrate and 540 mL water; then 120 mL and 480 mL
• 66 mL concentrate and 534 mL water; then 150 mL and 450 mL
• 54 mL concentrate and 546 mL water; then 100 mL and 500 mL

Show the answer and why

Answer: 60 mL concentrate and 540 mL water; then 120 mL and 480 mL

1+9 means one part concentrate to nine parts water, so the working solution is one part in ten, not one part in nine — that off-by-one is the commonest error in the whole of darkroom arithmetic. V₁ = V₂/(n+1) = 600/10 = 60 mL of concentrate, and the water is the remainder, 540 mL, so that the total is the 600 mL the tank actually holds. At 1+4 it is 600/5 = 120 mL of concentrate and 480 mL of water. Option 1 makes the classic mistake of adding the water to the full tank volume, which gives 660 and 720 mL and overflows the tank; option 3 divides by 9 and 4 rather than by 10 and 5. Note also which of the two answers is the more reliable in practice: ILFORD advise against measuring less than 10 mL of concentrate at a time, and both of these are comfortably above that, but a 1+50 developer in a 300 mL tank would need under 6 mL and the proportional error in measuring it starts to matter.

Question 2. A fixer bath cleared a scrap of film in 45 seconds when it was freshly mixed. Later in the same working session the test takes 2 minutes 30 seconds. What does that indicate and what is the correct action?

• The bath is fine; fix for 5 minutes from now on
• The bath is exhausted by the published rule, because the clearing time now exceeds twice the fresh figure of 45 seconds; mix a fresh bath rather than lengthening the fixing time
• The film is different from the one used for the first test; repeat with the original film
• The temperature has dropped; warm the bath and retest

Show the answer and why

Answer: The bath is exhausted by the published rule, because the clearing time now exceeds twice the fresh figure of 45 seconds; mix a fresh bath rather than lengthening the fixing time

ILFORD publish two separate rules that both come from the same measurement, and this question turns on the second. The first rule sets the fixing time: fix for twice the clearing time. The second rule retires the bath: discard the fixer once the clearing time in used fixer exceeds twice the clearing time in fresh fixer. Ninety seconds is that threshold here, and 2 minutes 30 is well past it. Doubling to a five-minute fixing time would be following the first rule while ignoring the second, and it does not work — the problem is not that fixing is slow but that the bath is loaded with silver and its by-products, and a film fixed in an exhausted bath retains complexes that washing cannot remove and that turn to silver sulfide over years. Note the useful cross-check: ILFORD publish 2 to 5 minutes as the fixing time for general-purpose film in fresh fixer at 1+4, so a clearing test implying five minutes is already at the far edge of their own range. Pour the old bath into the silver-bearing container, mix fresh, and measure the new clearing time as your next reference.

Question 3. A whole sheet comes back evenly thin, and the strip along the edge that was under the holder rail — which was never exposed to anything — is thin too. What does that rule out?

• It rules out under-development
• It rules out under-exposure, because the rail strip received no image light at all and its density therefore depends only on the processing
• It rules out an exhausted fixer
• It rules out a wrong development temperature

Show the answer and why

Answer: It rules out under-exposure, because the rail strip received no image light at all and its density therefore depends only on the processing

The rail strip is a built-in control, and it is free. It was covered throughout the exposure, so no image light reached it and its density is base plus fog: whatever the film and the processing produce with no exposure at all. That density is completely independent of how long the shutter was open. If the picture is thin and the rail strip is normal, the processing did what it always does and the fault is in the exposure. If the picture is thin and the rail strip is thin as well, something in the processing was short of what it should have been — the time, the temperature, the developer's strength or its age — and the exposure may have been perfect. This is the first move in reading any negative as evidence, and Part XXVIII builds a whole method on it: always find the part of the film that was not exposed and read that first.

Question 4. ILFORD publish a development time of 8½ minutes for FP4 Plus in ID-11 stock, and their table is headed "35mm and Roll Film". You are tray-processing a 4 × 5 sheet of FP4 Plus with continuous agitation. What time should you use, and how should you record it?

• 8½ minutes, recorded as ILFORD's published sheet-film time
• About 7¼ minutes — the tabulated time less the up-to-15-per-cent reduction ILFORD state for continuous agitation — recorded as the course's arithmetic on ILFORD's stated reduction, because ILFORD publish no sheet-film time of their own
• 12 minutes, because a tray develops more slowly than a tank
• Whatever a forum recommends for that combination

Show the answer and why

Answer: About 7¼ minutes — the tabulated time less the up-to-15-per-cent reduction ILFORD state for continuous agitation — recorded as the course's arithmetic on ILFORD's stated reduction, because ILFORD publish no sheet-film time of their own

Two separate facts have to be held apart. ILFORD publish a table for FP4 Plus, and its heading says which formats it covers: 35 mm and roll film. They publish no separate sheet-film development time. What they do publish that bears on your case is the instruction that where continuous agitation is used for manual processing, as in a dish or tray, the tabulated times should be reduced by up to 15 per cent — and separately, that continuous agitation by rocking the tray is what they recommend for sheet film. Applying their stated reduction to their tabulated time gives about 7¼ minutes, and that is a defensible number. What makes it honest is the record: it is your arithmetic on their instruction, not a figure they printed, and writing it that way means that when the negative comes out flat you will know which of the two to doubt. Option 3 has the direction backwards: continuous agitation develops faster, not slower, which is exactly why the reduction exists.

Question 5. Your film needs 9 minutes at 20 °C but everything in the room is at 24 °C. Using ILFORD's compensation chart, what time does it give, and what should you check before using it?

• 6¼ minutes, and check that this is not below the five-minute floor the same chart warns about, and that your film's own sheet does not publish its own compensation graph, which would take precedence
• 9 minutes, because the chart is only a guide
• 11¼ minutes, because a warmer developer needs longer
• 4 minutes, halving for every four degrees

Show the answer and why

Answer: 6¼ minutes, and check that this is not below the five-minute floor the same chart warns about, and that your film's own sheet does not publish its own compensation graph, which would take precedence

Read the chart rather than calculating: the row that gives 9 minutes at 20 °C gives 6 minutes 15 seconds at 24 °C. Two checks follow. First, the chart carries a printed warning that development times below five minutes are not recommended because of the risk of uneven development, and 6¼ minutes clears that comfortably — but a film needing 6 minutes at 20 °C would fall to 4 minutes at 24 °C, and the chart hands you that number without stopping you from using it. Second, ILFORD offer this chart as a general guide for all film and developer combinations, while some individual film sheets — FP4 Plus among them — publish their own compensation graph. A figure from the film's own sheet is more specific than a figure from a general chart, and where the two differ the specific one wins. Option 3 has the physics backwards: development is a chemical reaction, its rate rises with temperature, and warmer therefore means shorter.

Question 6. Why does an unspecified agitation scheme make a development time meaningless, even when the time and the temperature are both exact?

• Because agitation warms the developer
• Because agitation stirs the developer inside the emulsion layer
• Because agitation renews the exhausted, bromide-rich boundary layer at the emulsion surface, so how often it happens changes how much developing agent reaches the crystals — making it a third variable of the same standing as time and temperature
• Because inverting the tank exposes the film to light

Show the answer and why

Answer: Because agitation renews the exhausted, bromide-rich boundary layer at the emulsion surface, so how often it happens changes how much developing agent reaches the crystals — making it a third variable of the same standing as time and temperature

Nothing stirs inside the gelatin: the developer arrives at the crystals by diffusion, and its products leave the same way. What lies between the bulk solution and the layer is a thin stagnant film of liquid that becomes locally depleted of developing agent and locally loaded with the bromide released by development. Agitation sweeps that layer away and replaces it. Agitate more often and the crystals see fresher developer for more of the time, so density and contrast rise; agitate less often and both fall, and the depleted layer starts to drift under gravity, which is how streaks appear below dense areas. That is why every maker specifies a scheme alongside the time — ILFORD four inversions in the first ten seconds of each minute, FOMA continuous for thirty seconds then ten seconds a minute — and why the two schemes come with two different tables. Record the scheme you used, in words, every time: it is the variable most often left out of a notebook and most often responsible for two sessions that "did the same thing" and did not.

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