Capstone Stage 3: Exposing, Processing and Measuring

Purpose

To make the original negatives the portfolio will be printed from, process them in the solution you formulated and verified in Stage 2, and — the part that makes this a measurement rather than a session — attach a curve to every run, so that at the end you can say what the process did rather than what you meant it to do.

Requirements 3, 5 and 7 are all discharged here, and 7 is the one with teeth: a characteristic curve, a contrast index, a base-plus-fog figure, an effective exposure index, a clearing time with the capacity used, and a residual-thiosulfate result. Each with an uncertainty, each traceable to an instrument with a certificate.

This is the longest stage in the capstone — 480 minutes of time on task — and almost none of it is spent learning anything new. It is spent doing the same four things repeatedly and writing every one of them down.

Learning objectives

By the end of this stage you will be able to:

• run a shooting campaign as a planned sequence rather than a series of outings, with the technically riskiest subject taken first;
• work an exposure from a meter reading to a time given, through the effective f-number, your own fitted reciprocity trend and any filter factor, and say which term dominates;
• carry a control strip through the same tank as the film and read a curve from it;
• execute your own processing SOP and record a departure from it as a departure;
• derive contrast index, base plus fog and an exposure index from your own data, each under a named construction, and compare all three with your personal processing table;
• state which differences in your data are real and which are noise, using the two instrument certificates;
• run a residual-thiosulfate test and say precisely what it does and does not prove;
• diagnose a lost negative against Part XXVIII rather than guessing, and treat the failure record as a deliverable.

Prerequisites

Stage 1, with the instrument certificate and its operating notes, and Stage 2, with the developer verified and its version identifier issued.

From Part VI, pinhole exposure and reciprocity correction. From Part VII, the portfolio review, which is where your own reciprocity exponent and effective speed were fitted. From Part XII, your archival processing sequence and the wash-testing lab. From Part XIV, process control with control strips. From Part XV, the characterisation assignment, which owns the personal processing table. From Part XXVII, the development time series, which owns the contrast-index-against-time slope you will read a correction off.

The SOPs this stage executes: film processing, control-strip processing and charting, the clearing-time test, residual hypo and silver tests, loading a pinhole back and the outdoor or night exposure session.

Safety classification

Level A. This is ordinary film processing with the developer you formulated, a stop bath, a fixer and a wash, in a home darkroom or at a sink with a daylight tank: nitrile gloves and eye protection whenever solutions are handled, an openable window or an extractor rather than a sealed room, dedicated labelled utensils kept away from food and from food utensils, and the safety data sheet for every product to hand. The concentrated stock made in Stage 2 is diluted with the same precautions used to make it.

What is not a hazard here, and why. The bath the reader most often worries about — the fixer — is the least eventful thing on the bench at working dilution and room temperature. No step of this procedure heats anything, no step evolves a gas as written, and the acid and the thiosulfate meet only on the film, where the volumes are microlitres in a wet gelatin layer rather than the two litres in your waste corner. The reason that distinction holds is quantity and sequence, not the substances: the same stop bath poured into the same fixer bottle is the likeliest incompatibility accident in a home darkroom, and the difference between the safe case and the bad one is entirely which container they meet in.

Two things on this page sit at the top of Level A and are named here rather than in the procedure.

The residual-chemistry tests are a declared Level B step inside a Level A session, under the raised-step rule. The test solution is 1 per cent silver nitrate, and silver nitrate is Danger with H272, H290, H314, H318, H360D, H400 and H410 — an oxidiser that causes severe skin burns and serious eye damage. For that step and no other: sealed chemical splash goggles rather than spectacles, nitrile gloves changed the moment either solution touches them, an apron, its own labelled dropper bottle, the bench cleared of everything else, and the solution, its rinse and the tested strips collected as silver-bearing waste rather than rinsed away. Eyewash within reach before the bottle is opened. If you do not have those controls, the test is not performed here — it is carried in from Part XII’s wash-testing lab, which is a Level B session throughout, or it is recorded as not performed with the reason.

The shooting phase carries the ordinary field risks of a long-exposure project — working at night, near water, near traffic, on private land, alone — and they are real, are not chemical, and belong in the project plan’s assessment rather than here. A tripod standing on a pavement for forty minutes is a highway obstruction question before it is a photographic one.

Hazards

What	Why it matters at this bench
Developer, at working dilution	The developing agents are skin sensitisers; prolonged skin contact is the commonest darkroom dermatitis and gloves are the control
Stop bath, dilute acid	Eye irritant; and it must never reach the fixer bottle or the sulfite container
Fixer, at working dilution	Eye irritant; the spent bath is silver-bearing and is the stream that goes to recovery
Silver nitrate test solution, 1 per cent	Danger: H272, H290, H314, H318, H360D, H400, H410. Stains skin black, and the stain is the visible proof that a control failed
Sodium sulfide test solution, diluted 1+9	Its own encyclopaedia entry governs the stock, which is made once, elsewhere, as a separate operation; at this bench it exists only as a dosed solution, and no acid comes to this bench
Field work	Traffic, water, darkness, private land, cold. Not chemical, and the most likely thing to hurt you in this stage

Required PPE

Nitrile gloves and eye protection whenever a solution is handled, throughout. For the declared Level B step: sealed splash goggles, gloves changed on contact, and an apron. Tongs or a film clip rather than fingers for anything coming out of a bath. In the field, whatever the field needs — a torch you can work by, high-visibility clothing near a road, and somebody who knows where you are for a night session.

Ventilation

An openable window or an extractor running, because a stop bath and a fixer are open in the room for the length of the run. This is dilution ventilation for a low-level acid odour rather than control of a specific vapour, and it is the same provision Parts VI and XIX assume. For the residual test, the control is separation and containment rather than airflow: nothing here evolves a vapour, and the reason no acid comes to that bench is the sulfide, not the air.

Materials

Material	Quantity	Note
Film or plates, from one emulsion batch	The campaign’s total, with your own redundancy factor applied	One batch. A top-up from another batch is a different material and will sit inside your data looking like chemistry
Unexposed control sheets or strips	One per processing batch	For the residual tests; processed identically, in the same run
A 21-step transmission wedge	1	For the control strips
Negative sleeving	The campaign’s total	Named in the price file’s own gap list: sleeving that passes the Photographic Activity Test is unpriced
Contact proof paper	2 to 4 sheets	The working index for Stage 4

Chemicals

Chemical	Quantity per run	Form
Your formulated developer, by its version code	473 mL of stock per two 135-36 rolls at 1+1	Stock, diluted just before use
Citric acid or acetic acid stop bath	20 mL of concentrate	Working dilution per the product sheet
Ammonium thiosulfate rapid fixer	120 mL of concentrate, at 1+4 for film	Working solution, capacity logged
Wetting agent	3 mL	At 1+200 for the final rinse
Silver nitrate	1 g, as 100 mL of 1 per cent	The residual-thiosulfate reagent
Sodium sulfide stock, if the silver test is run	A few drops of the 1+9 dilution	Stock made once, elsewhere, under its own controls

Equipment

The instrument from Stage 1 with its certificate and operating notes; a meter; a tripod; the sensitometer and densitometer with their certificates; a daylight tank and reels, or a changing bag and tank; a thermometer you have verified; a stopwatch; drying clips; a loupe. None is consumed and none appears in the table below.

Estimated cost

££ on the planner’s bands, and the campaign’s dominant cost is film. The capital — tank, reels, thermometer, instruments — already exists by this point in the course, and the planner carries it. What follows is one processing run; a capstone will contain something like six to ten of them.

Estimated consumables cost

Every figure with a source is the planner’s own dated UK price and every quantity comes from the Materials and Chemicals sections. The run costed is two 135-36 films plus one control strip through one tank, developed in D-76 at 1+1 one-shot, with one residual-thiosulfate test at the end.

Consumed	This session	Sourced price	Cost this session
Film, one emulsion batch	2 rolls of 36	£6.37 to £11.40 a roll	£12.74 to £22.80
Formulated developer stock	473 mL, diluted 1+1 and discarded	£3.30 to £3.93 per litre of stock, from Stage 2’s own table	£1.56 to £1.86
Stop bath concentrate	20 mL	£10.66 to £12.18 per 500 mL	£0.43 to £0.49
Rapid fixer concentrate	120 mL, at 1+4	£21.05 to £25.98 per 1 L	£2.53 to £3.12
Wetting agent	3 mL	£28.70 per 1 L	£0.09
Silver nitrate, for the residual test	1 g, as 100 mL of 1 per cent	£59.95 for 25 g to £112.90 for 10 g	£2.40 to £11.29
Sodium sulfide stock, if the silver test is run	a few drops of the 1+9 dilution	The price file could not price it. Sodium sulfide is a gap it names, and the residual-silver test is one of the reasons it gives	—
Negative sleeving	2 to 4 sheets	Named in the price file’s own gap list as unpriced	—

The priced rows come to about £19.74 to £39.64 for one run, and that is a floor and not a total: two of the eight consumables have no sourced price, and the wide silver nitrate range is a pack-size artefact rather than a real spread — the 25 g jar is much cheaper per gram than the 10 g one, and one capstone uses a few grams. Multiply the film, developer, stop and fixer rows by the number of runs in your campaign; the silver nitrate row is bought once and used for years.

Waste streams

Spent developer, alkaline, one-shot at 1+1 and therefore discarded after each run, collected separately from anything acidic. Spent stop bath, acidic, kept away from the fixer and from the sulfite. Spent fixer, silver-bearing, retained for silver recovery and never combined with the developer. The silver nitrate test solution, its rinse and the tested strips, all silver-bearing, collected rather than drained. The sulfide test drops and their blotting paper, in a container of their own that has never held a stop bath or a fixing bath. Wash water carries the residue the wash removed and is the one stream with no separate container.

Local regulation governs disposal and this page gives no jurisdiction-specific instruction; read the disposal caveat.

Alternative route

No darkroom. A changing bag and a daylight tank run this entire stage. Film is loaded in the bag, processed at a sink with the lights on, and the control strip rides through the same tank exactly as it would in a darkroom. The sensitometer exposes strips in its own light-tight enclosure, so it needs no dark space either. Nothing in Stage 3 is lost, which is worth saying plainly because it is the last stage of which that is true: Stage 4’s enlargement is where the darkroom requirement becomes real.

No sensitometer. Substitute Part XIII’s enlarger exposure series, at a stated cost: the exposure axis becomes relative rather than absolute, so the contrast index survives intact and the exposure index becomes a figure comparable only with your own other measurements. Requirement 7 is still met — it asks for an effective exposure index under a named criterion, not for an absolute speed — but the record must say which axis it was measured on.

Unable to handle silver nitrate. The residual-thiosulfate result becomes unavailable and there is no substitute for it at this bench: the alternative reagents in the literature are a permanganate test whose blank against oxidisable organic matter the course has not verified, and instrumental methods that need a laboratory. Record the row as not testable, with the reason stated as a property of your circumstances rather than of the test, and carry that forward into Stage 6’s permanence statement, where the measured sentence will be missing and has to say so. The specification caps the accuracy criterion at band 3 for this substitution, and that is the honest price.

Preparation

Fix the run order before the first outing, and put the technically riskiest subject first. The riskiest is not the most difficult picture; it is the one whose failure you can least afford to discover late — the long night exposure, the tide that happens twice a month, the subject that needs a permission. Shooting it first buys you the option of repeating it, and a campaign planned the other way round routinely discovers in week seven that its keystone picture is unusable.

Open the exposure log with the campaign’s header: instrument, configuration, focal distance, hole diameter, film batch, and the certificate date under which the instrument’s numbers are being quoted.

Mix and label the working solutions on the day, dilute the developer just before use, and measure the fresh clearing time of the fixer on a film leader before the first film goes in. That figure is the reference every later capacity judgement is made against, and it cannot be recovered afterwards.

Set the resolution decision, in writing. Before the first strip is read: what is the smallest difference in contrast index that will count as a difference, the smallest shift in the speed point, and the smallest change in base plus fog. Take them from your two certificates, not from preference. Part XXVII owns the method, and its rule applies here unchanged: a limit chosen after the numbers are seen is not a limit.

Procedure

The shooting phase

1. One log entry per sheet or frame, written at the moment of exposure. Not afterwards, not from memory in the car. The log’s fields are the ones the exposure log sheet already carries, and the entry is made before the shutter closes on the next one.
2. Meter, and record the method with the reading. An incident reading and a reflected reading of the same scene are different numbers, and six weeks later the number without its method is a number you cannot use.
3. Work the exposure through in the order the arithmetic runs, and write down every intermediate value:

🧮DO THE MATHS: from a meter reading to a time given

Start with the metered time at a reference aperture, then correct for the effective f-number your Stage 1 calculation produced. Doubling the f-number multiplies the exposure by four; the relation is the square, and it is the largest single factor in a pinhole exposure.

Then the reciprocity correction, from your own fitted trend. The relation the course uses is ILFORD’s:

T_c = T_m^P

Reciprocity correction

T_m is the metered time in seconds, T_c the corrected time, and P the exponent. ILFORD state that exposures of one second or less need no compensation, which is what makes the power law usable — it is anchored at one second, where the correction is exactly one.

ILFORD publish P = 1.31 for HP5 Plus, and their own worked example is 10 seconds becoming 20.4. Your fitted exponent from Part VII is the one to use inside the range you fitted it over, and the generic table is what you fall back on outside it. Say which you used, every time.

Then the filter factor, if there is one, from the manufacturer’s published figure.

Then look at the three corrections together and say which dominates. At a metered 10 seconds and P = 1.31 the reciprocity term is a factor of 2; at a metered 1000 seconds it is a factor of 8.5, and at that point the correction is most of the exposure rather than a trim on it. That is the sentence the night pictures live by, and it is also why a fitted exponent known to ±0.08 matters more at the long end than anywhere else.

4. Bracket to a stated policy, and state it before the campaign rather than deciding sheet by sheet. A useful default: bracket the technically uncertain exposures by ±1 stop in half-stop steps, and do not bracket the ones your log already predicts confidently — because a bracket that always contains a good sheet tells you nothing about whether your arithmetic works. The bracket is an experiment about your own exposure model, and it only returns information if the middle sheet was a prediction.
5. Note the departures as they happen. The cloud that arrived, the tripod that moved, the exposure you cut short. These are the entries that make a failure diagnosable later.

The processing run

6. Expose a control strip on the same material in your sensitometer, and load it into the tank with the film. Same emulsion batch, same run, same everything. This is the step that turns processing into measurement: every negative in the run now has a curve attached to it.
7. Execute your own SOP as written, and where you depart from it, write the departure down as a departure rather than silently making the session match the document. A capstone whose SOP and whose run records agree perfectly for eight runs is a capstone whose run records were written from the SOP.
8. Hold the temperature and record it — the developer, the stop, the fixer and the wash — at the start and at the end of the run, not once at the start.
9. Agitate to a stated scheme, written in words rather than as “normal”. Agitation is one of the four factors that move contrast index, alongside time, temperature and the developer itself, and it is the only one of the four that is usually left undescribed.
10. Measure the clearing time again at the end of the run, on a leader from the same film. Under the Part XI criterion the bath is fit while a piece of the film clears in no more than twice the time it took in that bath when fresh, and material is fixed for twice the clearing time measured on the day. Log the sheet count against ILFORD’s published unreplenished capacity of 24 films of 135-36 per litre at 1+4, and retire on whichever comes first.
11. Wash to the SOP. For film in a spiral tank, ILFORD’s method is fill, invert five times, drain; refill, invert ten; refill, invert twenty; then the wetting-agent rinse at 1+200.
12. Dry without marks, hung in still, clean air, and cut and sleeve only when completely dry.

The measurement

13. Read all twenty-one steps of the control strip, plus the unexposed strip for base plus fog, on your densitometer, following the preflight routine its certificate specifies.
14. Plot density against log exposure, and derive the three numbers under their named constructions: contrast index under the course’s convention, base plus fog from the unexposed strip, and the exposure index under the course’s speed criterion.
15. Compare all three with your personal processing table, and decide.

The residual test

16. Run the residual-thiosulfate test on one negative from the run, or on the unexposed control sheet carried through with it, by the SOP, under the Level B controls named above. Kodak’s own instruction for film is a strip cut from the clear margin and immersed about three minutes, with a well-washed film showing very little or no discoloration — and the spot technique is not used on wet film, because the reagent spreads.
17. Record the reading in words, at the bench, against the untreated half of the same sheet. Keep the result: Stage 6’s permanence evaluation reads it.
18. Write down which reagent you mixed, by name, in the same entry. A plain 1 per cent silver nitrate immersion is Kodak Limited’s 1949 test and is not HT-2, which is acidified with acetic acid and read against a card this course does not hold. Stage 6 sets out the naming rule and why the two designations are not interchangeable; the discipline starts here, because this is the entry the permanence statement will quote.

Expected observations

On the negatives. A campaign shot at long exposures will look contrastier than your test negatives did, and that is not a processing fault — ILFORD state plainly that contrast is increased with long exposures and that pulling the development may be required. Expect it, and expect it to show up in the control strip as a higher contrast index than the same time gave in Stage 2, because the strip and the film went through the same tank but the strip was exposed at ordinary intensities and the film was not. That divergence is real information about your subject, not a discrepancy to be reconciled.

On the control strip. A recognisable characteristic curve: a toe, a straight section and a shoulder. Across a family of runs, the shape you already know from Part XV — the toe stays put while the straight line and the shoulder steepen.

On the clearing time. A fixer’s decline gives almost no warning. Two thirds of a bath’s life is spent in a region where the clearing time has changed by less than a fifth, which is inside the resolution of a stopwatch and an eye, and then it bends up sharply. Measuring every run is what catches the corner; waiting for something to look wrong does not.

What is happening chemically

Three mechanisms, all taught elsewhere, all governing something you will see.

Reciprocity failure is a competition between latent-image formation and its own thermal decay. At low intensity the silver atoms arriving at a sensitivity centre come slowly enough that a sub-latent speck can disperse before the next one arrives, so a longer exposure buys less than proportionally more developable grains. That is why the correction is a power law with an exponent above one rather than a constant factor, and why it vanishes at short exposures where the arrivals outrun the decay. Part IV owns the mechanism.

Development is a contrast control and only marginally a speed control, which is why the family of curves fans out from a nearly common toe. The speed point sits at a density only 0.10 above base — on the part of the curve that barely moves — while the straight line and the shoulder steepen with time. Your own data from Part XV is the evidence, and it is the reason step 15’s decision is usually about time rather than about anything else.

Fixing is complex formation and it goes in stages. Thiosulfate converts silver halide first to sparingly soluble complexes and then to soluble ones, and a film that has cleared has only reached the end of the visible part of that sequence. That is why material is fixed for twice the clearing time rather than until it clears, and it is the chemistry behind the whole residual-silver question that Stage 6 will return to. Part XI owns it.

Data to record

Into the exposure log, the lab notebook and the curve-plotting sheets, which between them already carry every field below.

Per exposure: identifier; date and time; subject; instrument and configuration; focal distance; hole; effective f-number; metered value and metering method; computed time; reciprocity correction with the exponent used and whether it was yours or published; filter factor; the time actually given; bracket position; and the conditions and departures.

Per run: the developer’s version code, dilution and temperature at the start and end; the agitation scheme in words; the fixer’s fresh and end-of-run clearing times and its running sheet count; the wash route; and every departure from the SOP with the reason.

Per control strip: the twenty-one densities with the reading method’s own resolution beside them; base plus fog from the unexposed strip; contrast index, exposure index and their constructions named; and the instrument serial and certificate date.

Per test: the residual reading in words, against the untreated half, with the light it was read in.

Analysis

The three numbers, and what to do with them

Contrast index against the table. The window is ±0.02, the figure Part XV adopted from Kodak’s process-control practice. Convert it to minutes through the slope of your own contrast-index-against-time plot before deciding anything: at 0.03 of contrast index per minute, ±0.02 is ±0.7 minutes, and a development time quoted to the nearest fifteen seconds is spurious.

Base plus fog against the table. A rise with normal contrast points at the bath or at the film rather than at the development, and the discriminating test is an unexposed strip from a second box.

Exposure index against the table. Under the course’s criterion, and written in the course’s form — “EI 320, measured under the criterion defined in Part XIII, which is modelled on ISO 6, on emulsion batch NNN in [version code] at 20 °C for N minutes, read on instrument serial NNN under its certificate of [date]”. Never “the ISO speed is 320”.

The uncertainty statement, which is what the numbers require

Where each term comes from, and the one legal bridge between the two axes

1. 1Log exposure terms, from the sensitometer certificateWedge step values, uniformity across the wedge, lamp and instrument drift, timing. These say where a step sits sideways.
2. 2Density terms, from the densitometer certificate, BY BANDRepeatability with the sample replaced, the wedge certificate, chain non-linearity, the stray-light residual. Not one figure for the instrument: the band where base plus fog sits and the band where the shoulder sits are different numbers.
3. 3The bridge: divide a density term by the local gradient GA spread of 0.03 in density is 0.05 in log exposure where the gradient is 0.6 and 0.20 where it has fallen to 0.15 on the shoulder. Write G down beside every conversion.
4. 4Never add across the gap0.02 in log exposure and 0.02 in density are not the same 0.02, and adding them because both are "about 0.02" is how a budget becomes fiction.
5. 5The sentence that comes outWhich differences in your data are real, and which are noise. It is a sentence, not a table, and it belongs in the chemistry report as well as here.

The figures are read off your own two certificates rather than restated here, because a number quoted from this page would be a number about somebody else's instrument.

Read the certificate rather than remembering a number from it. A densitometer certificate quotes its repeatability by density band, and the band matters: the same instrument that resolves 0.01 between 0.0 and 2.0 may be limited by its stray-light floor above 2.5, in which case a shoulder density is not quoted at all. If your certificate says an instrument may not be used to claim something, that is a statement about your data.

The decision that closes the stage

Three outcomes, and all three are legitimate.

1. The process is where you aimed it. Go on with the rest of the campaign unchanged, and keep measuring — the point of a control strip is the run after the one that was fine.
2. It is off, and time will reach it. Move the development time along your own slope, re-verify on the next run’s strip, and record the change with the run it took effect from. Every negative afterwards traces to the new time; every negative before it traces to the old one. That is why the run record exists.
3. It is off and time will not reach it. Something has changed that is not development: a new film batch, an exhausted fixer carrying over, a thermometer that has drifted, a developer past its keeping figures. Diagnose before remixing.

And then decide which negatives go forward. Read the contact proof sheet and the curve together: the proof says what is on the negative, the curve says whether the material was processed where you intended. A picture you like on a run whose contrast index came out 0.08 high is a printable negative with a known reason for being hard to print, and knowing the reason is worth more than the sheet.

Troubleshooting

Diagnose against Part XXVIII rather than guessing; this table is a signpost to it, not a replacement.

What you see	Where it is diagnosed	The discriminating evidence
Fog across whole frames, worse on longer exposures	Fog and where it comes from	A leak grows with exposure time; a fogged batch does not. Sort the affected sheets by exposure length
Streaks or marks following the sprockets or the reel	Uneven development and flow marks	The agitation scheme, and whether the marks move when it changes
A negative thinner than the log predicts, consistently	The exposure model, not the process — the control strip in the same tank will be normal	Compare the strip’s contrast index with the table. Normal strip plus thin film means exposure
Everything thin, strip included	Development: time, temperature, agitation or an exhausted bath	The version code and the run record. A one-shot dilution cannot be exhausted, so look at temperature first
Milky or opalescent negatives after fixing	Incomplete fixing	Clearing time at the end of the run against the fresh figure. Refix in fresh bath and record it
Drying marks	The wetting-agent rinse — too little and too much both give uneven drying	Measure the dilution rather than eyeing it, and do not agitate it hard, because it foams
The residual test yellows	The wash, not the fixing	Fixing, washing and stains, and rewash the batch
An unrepeatable, unexplained fault	Diagnosing unknown faults	Change one thing at a time, and keep the sheet

Clean-up

Discard the one-shot developer into its own container, the stop into its own, and the fixer into the silver-recovery container. Rinse the tank, the reels and the graduates in that order and dry the reels completely — a damp reel is the commonest reason a film will not load next time, and a film that jams in a changing bag is a film with a fold in it. Wipe the bench. The residual-test bench is cleared separately, with its own waste containers, and the dropper bottle goes back to its labelled place away from the working surfaces.

Storage

Negatives are the irreplaceable object in this whole project, and Stage 4 onwards depends on their being findable rather than merely kept.

Dry completely, then sleeve. Use enclosures chosen on the conservation criteria rather than on convenience — the Photographic Activity Test is what qualifies an enclosure material, and the price file names PAT-passing sleeving among the things it could not price, which is a supply problem rather than a permission to use anything. Label every sleeve so that the negative and its log entry cannot be separated: the run identifier, the frame identifier, the date, the developer version code and the control-strip reference. A negative whose sleeve carries only a date is a negative whose curve you will not find.

Store flat or hanging, cool, dry and dark, away from any room where sulfide toning is done. Make the contact proof sheet now, while the run is fresh, and index it to the log — it is the working document of Stage 4 and it is much cheaper to make in a batch than one strip at a time.

Disposal considerations

The developer stream is alkaline and carries the developing agents’ aquatic hazard classifications. The fixer stream is silver-bearing and goes to recovery, both because silver is a controlled discharge and because it is worth recovering. The stop bath is acidic and is the stream that must never meet either of the others in a container. The silver nitrate test solution, its rinse and the tested strips are silver-bearing waste; the sulfide drops go in their own container that has never held a stop bath or a fixing bath, because acid and sulfide give hydrogen sulfide.

Local regulation governs disposal, and this page gives no jurisdiction-specific instruction. What route your streams may take is a question for your water authority and your local authority, and the disposal page explains why the course states the chemistry and stops there. Check your local regulations; they govern.

Questions

1. Your metered time is 240 seconds and your fitted exponent is 1.22, fitted over the range 4 to 120 seconds. What time do you give, and what do you write in the log about the exponent?
2. A run’s control strip gives contrast index 0.64 where the table predicts 0.58, but the negatives from the same tank print easily at grade 2. Reconcile the two observations.
3. Your clearing time is 1.8 times the fresh figure after eighteen films through a litre. What does the Part XI criterion say, what does ILFORD’s published capacity say, and which governs?
4. The densitometer certificate gives repeatability of 0.008 in the 0.0 to 1.0 band and 0.025 above 2.5. You measure a shoulder density of 2.9. What may you claim about it?
5. Your residual-thiosulfate test on the control sheet shows no colour difference. Write the sentence that goes in the record, and one sentence saying what it does not establish.
6. You change the development time after run 4. What has to be recorded, and where, so that a reader in ten years can tell which negatives were processed under which time?

Further experiments

Fit your exponent again, on this campaign’s data. You fitted one in Part VII on paper negatives; this campaign is on film, and the exponent is a property of the material. Plot log of the time given against log of the metered time for every sheet you judged correctly exposed, and read the slope and the intercept. The slope is your exponent on this film; the intercept is a speed error. Compare with the manufacturer’s published factor and say what the difference is.

Measure the long-exposure contrast rise. Expose the same subject at a metered 1 second and at a metered 300 seconds, corrected so both should be equally exposed, and develop them in the same tank. Read both. ILFORD state that contrast rises with long exposures; this measures how much, on your film, and it is a number that will change how you develop the night pictures.

Test the control strip’s own stability between runs. Expose three strips in one sensitometer session, develop one in each of three runs across the campaign, and read all three. The spread is the combined drift of your sensitometer, your developer and your technique, and it is the honest floor for every between-run comparison you make.

Spend one film learning the fixer’s corner. Process one film at a time through a litre, measuring the clearing time each time, and plot it. You will see the flat region and the bend, and you will never again judge a fixer by looking at it.

Check your understanding

Question 1. Why must the control strip be developed in the same tank as the film rather than in a separate tank of the same developer at the same time?

• It need not be; two tanks of the same developer at the same temperature are equivalent
• Because the strip is the record of what that particular tank did — its temperature history, its agitation, its carry-over and its degree of exhaustion — and a strip from a different tank measures a different process however similar it looks
• Because a separate tank would need a second control strip
• Because film and strips must always be developed together for the fixer capacity to be logged correctly

Show the answer and why

Answer: Because the strip is the record of what that particular tank did — its temperature history, its agitation, its carry-over and its degree of exhaustion — and a strip from a different tank measures a different process however similar it looks

The strip exists to attach a curve to a specific run, and every one of the four factors that move contrast index — time, temperature, agitation and the developer itself — is a property of a tank rather than of a formula. Two tanks filled from one bottle diverge the moment one of them is agitated differently, warmed by a hand, or carries over more stop bath. Fixer capacity is logged from the sheet count and is unaffected either way, which makes the last option a plausible-sounding irrelevance.

Question 2. ILFORD publish P = 1.31 for HP5 Plus. You fitted P = 1.22 over the range 4 to 120 seconds from your own logs. Your next exposure meters at 900 seconds. Which do you use?

• Your own, because a personal fit always supersedes a generic table
• ILFORD's, because a manufacturer figure is a Tier 1 source and a personal fit is not
• Your own if you say so, but the honest position is that 900 seconds is far outside the range you fitted over, so the published factor is the better estimate there and the record states which was used and why
• Neither: above about 100 seconds the power law breaks down and only a bracket will do

Show the answer and why

Answer: Your own if you say so, but the honest position is that 900 seconds is far outside the range you fitted over, so the published factor is the better estimate there and the record states which was used and why

A fitted trend supersedes a generic table only inside the range it was fitted over, and 900 seconds is nearly an order of magnitude beyond 120. Extrapolating an exponent is exactly the error the two-point pH calibration makes at pH 8.6, in a different currency: the line may be fine, but nothing in your data says so. What the situation actually calls for is the published factor, a bracket wide enough to cover the disagreement between the two exponents at that duration — which is substantial — and a log entry that records both figures so the sheet becomes another point in your own fit.

Question 3. Your densitometer certificate quotes repeatability of ±0.008 between 0.0 and 1.0, and states that the scale above 2.5 is limited by stray light and is not quoted. Your control strip's highest step reads 2.9. What may you write?

• "Maximum density 2.9 ± 0.008"
• "Maximum density 2.9", since the repeatability figure applies to the instrument as a whole
• That the highest quoted step is the last one inside the certified range, and that the reading at 2.9 is outside what this instrument may be used to claim — recording it as an observation with that limitation attached rather than as a measurement
• Nothing: a reading outside the certified range must be discarded

Show the answer and why

Answer: That the highest quoted step is the last one inside the certified range, and that the reading at 2.9 is outside what this instrument may be used to claim — recording it as an observation with that limitation attached rather than as a measurement

A certificate that says what an instrument may not be used to claim is doing its most important job, and honouring that is what makes every other number on the page trustworthy. The reading is not worthless — it tells you the shoulder is up there — but it cannot carry an uncertainty, so it is an observation rather than a measurement and the record says so. Attaching the low-band repeatability figure to a high-band reading is the specific error the certificate's band structure exists to prevent, and discarding the number entirely throws away information you paid for.

Question 4. Your campaign is shot at exposures of several minutes. The control strips, exposed in the sensitometer at ordinary intensities, come out at the contrast index your table predicts — but the negatives are visibly contrastier than your test negatives were. What is the explanation, and is anything wrong?

• The sensitometer is out of calibration, since it and the film disagree
• Nothing is wrong: ILFORD state that contrast is increased with long exposures, so the film and the strip genuinely received different treatments before they met in the tank, and the remedy — if you want one — is to pull the development for the long-exposure runs
• The developer is exhausting between the strip and the film
• The negatives are over-exposed, and the reciprocity correction is too large

Show the answer and why

Answer: Nothing is wrong: ILFORD state that contrast is increased with long exposures, so the film and the strip genuinely received different treatments before they met in the tank, and the remedy — if you want one — is to pull the development for the long-exposure runs

The strip and the film went through the same tank, so development is not the variable — what differs is the exposure that preceded it, and reciprocity failure does not act uniformly across a negative's tonal range. ILFORD say so directly in the same document that gives the correction: contrast is increased with long exposures and pulling the development may be required. The right response is to treat it as information about the subject rather than as an instrument disagreement, and either to develop the long-exposure runs shorter or to print them at a lower grade, having recorded which runs were which. An over-exposure would raise density without preferentially raising contrast.

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