Lab: Preparing Standard Test Negatives

Everything measured in the rest of Part IX is measured against what comes out of this session. Not the pictures — there are no pictures — but the batch: forty-odd identical strips of film, exposed from one geometry in one sitting, of which a few are developed today to find out how well the whole arrangement can repeat itself.

The strips are the cheap part. The discipline that keeps them identifiable is the content, and the test of this page is not whether you produce a negative today but whether, in a year, Part XXVII can pick a strip out of a sleeve and know exactly what was done to it.

Purpose

To build a fixed-geometry contact-exposure rig; to cut and notch a batch of film strips in darkness; to expose every strip in the part from that one rig in one sitting so that exposure is a constant rather than a variable; to process a control set in D-76 1+1 at 20 °C and read it; and to establish from that control set the resolution limit — the smallest difference the rest of the part is entitled to call real.

Learning objectives

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

• Set up a contact-printing geometry whose illumination is even to better than a tenth of a wedge step, and say why the lamp distance is what makes it so.
• Choose an exposure time by pilot bracket and correct it by a stated number of wedge steps, allowing for reciprocity where the exposure is longer than a second.
• Cut film to length and notch it by touch in total darkness, and explain why the identity code is applied later rather than now.
• Process a set of strips in a cylinder to a published time with a written agitation script.
• Read base plus fog, the threshold step and the scale length off a dried strip.
• State your own rig’s resolution limit as a number, in wedge steps.
• Label, sleeve and file a strip so that its identity survives without you.

Prerequisites

• Experimental design for the darkroom, which owns the readings, the replication arithmetic and the notebook fields used here.
• Lab: mixing D-23 and D-76, which produced the D-76 stock this session dilutes. A bought developer will work and will not be a control, because you will not know what is in it.
• Lab: processing your first film, for the clearing-time test, the wash and the drying, none of which is repeated here.
• Measurement and uncertainty and concentration and dilution.
• The SOPs for opening the laboratory, mixing from a stock and labelling a container, which this page cites rather than restates.

Safety classification

Level A: a standard home darkroom, with two hazards that are not chemical.

• Solutions only. Nothing is weighed out. The developer is diluted from a stock mixed in Part VIII, and the fixer and stop are proprietary liquids diluted to the maker’s figures. Handled by the hundred millilitres, with gloves and eye protection, that is squarely Level A, and it is the same handling as Part VI’s processing lab.
• Cutting in darkness is the real hazard on this page, and it is a mechanical one. Scissors or a blade, worked by touch, next to a bench you cannot see. It is controlled by laying the bench out before the light goes off and not changing it afterwards, by using a jig with a fixed stop so the cutting hand has a known path, and by keeping the other hand behind the blade.
• A mains lamp near liquids. The exposure rig runs on mains and the wet bench does not go near it. They are separated by the room’s wet and dry areas, not by care.
• Waste. Spent developer in one labelled container; the fixer and its first rinse, which are silver-bearing, in another.

What is not a hazard here, and why. There is no dust exposure at any point, because no powder is opened: the sensitisers metol and hydroquinone are already in solution and stay there, and the inhalation route that makes Part VIII’s weighing step a Level B operation simply does not exist on this page. There is no sulfur dioxide risk either, even though the developer carries a hundred grams of sulfite per litre of stock. Sulfite releases that gas on meeting an acid, and this session contains no acid at any point: Part IX uses a plain water rinse in place of a stop bath, for a reason given under Procedure, and the fixer is met only after that rinse and goes to its own container. The risk is real one bench along, in the waste bottle, which is why the developer and fixer wastes are never combined and why the incompatibilities page treats that separation as a control rather than a tidiness preference. And nothing here is heated: the warmest thing in the room is a water bath at 20 °C.

Hazards

Metol and hydroquinone in solution: skin sensitisation. Metol carries H317, may cause an allergic skin reaction, in every ECHA notification that classifies it, and hydroquinone carries it too. In solution the route is skin contact rather than inhalation, and it is met by gloves and by keeping fingers out of the vessels. Sensitisation does not reverse.

Rapid fixer: eye and skin irritation, and a smell that is not the hazard. Follow the supplier’s own safety data sheet for the product you have; the course does not restate a classification for a mixture whose composition it has not read.

Acid meeting sulfite waste. Not a hazard within the procedure, which uses no acid, and a real one in the waste bottle if an acid stop or an acid fixer from another session reaches it. Two containers, labelled, never combined.

Cutting by touch. Sharp edges worked blind. The film itself is a hazard in miniature: a freshly cut film edge will open a finger.

Wet floors and a dark room. The commonest injury in a darkroom has nothing to do with chemistry. Everything on the floor is moved before the light goes off.

Aquatic toxicity of the developer waste. Both agents are notified as very toxic to aquatic life with long-lasting effects, and a session that develops a handful of strips consumes almost none of them, so essentially all of what was weighed in Part VIII is still in the waste bottle.

Required PPE

• Single-use nitrile gloves, 0.2 mm, the splash-resistant grade HSE’s COSHH essentials sheet P1 specifies for manual film development. Changed when contaminated and thrown away at the end.
• Eye protection whenever a solution is being poured or agitated.
• An apron or overall kept for laboratory work.
• Dry, clean hands for the film itself. The Library of Congress’s handling guidance — freshly washed hands, or clean lint-free cotton or inert plastic gloves, and never a finger on the image area — is the control that protects the archive rather than you. Handle every strip by its edges, wet or dry, for the rest of the part.
• Dedicated, labelled utensils, never used for anything but photographic chemistry.

Ventilation

Ventilation is not being asked to remove a vapour here; nothing on the bench evaporates at 20 °C in a way that puts anything into the air. It is doing two other jobs, and HSE’s COSHH essentials sheet P1 sets the standard for both: general ventilation above five air changes an hour with a through draught, to keep the room’s air turning over during a three-hour session, and to carry away the ammonia smell of a rapid fixer, which is an amenity problem rather than a control failure but will drive you out of the room if the door stays shut.

The awkward part is that a darkroom must be light-tight and ventilated at once. The answer is a light-trapped vent or a baffled extractor rather than an open door, and it is Part II’s laboratory layout that owns it.

Materials

Item	Quantity	Note
Film, one emulsion batch	four 36-exposure 35 mm cassettes, or one 30.5 m bulk tin	ILFORD FP4 Plus is the course’s reference; the batch number goes in the notebook
Transmission step wedge	1	Stouffer T2115 or equivalent: 21 steps at a nominal 0.15, half a stop each, to a maximum density of 3.05
Opaque card	a strip 15 × 40 mm	The mask that gives every strip its own unexposed patch
Negative filing sheets or glassine envelopes	enough for 45 strips	Two 135 mm strips fit head to head in one 35 mm sleeve pocket
Card label slips	45	One per pocket, written in pencil or a pigment pen

Chemicals

Nothing is weighed. Every solution on this page is diluted from a stock or a concentrate, following the SOP for mixing from a stock.

Chemical	Quantity	Form
D-76 stock, from Part VIII’s lab — metol, hydroquinone, sodium sulfite, borax	250 ml	Solution, diluted 1+1 just before use and discarded after one batch, as Kodak’s J-78 sheet directs
Plain water rinse, at 20 °C	600 ml, in two changes	The course’s choice for the whole of Part IX, in place of a citric acid stop; ILFORD note that a water rinse may be substituted but increases the risk of processing marks and stains
Rapid fixer, ammonium thiosulfate type, or a sodium thiosulfate fixer	300 ml at 1+4	Fixed for twice the clearing time, measured on a scrap
Wetting agent	300 ml at 1+200	Final rinse; ILFORD warn that too little or too much both give uneven drying

Equipment

An exposure rig, a cutting jig, and the wet bench.

The exposure rig. A baseboard; a channel or a pair of rails 36 mm apart to locate the film; the wedge; a sheet of 3 mm glass to hold wedge and film in contact; a lamp on a stand at 1.00 m above the film plane, left burning throughout; and a card shutter — a piece of opaque card held over the wedge and lifted for the exposure. A stopclock reading to 0.1 s.

The cutting jig. A flat board with a straight cutting edge and a hard stop 135 mm from it; scissors or a film cutter; a nail clipper or a single-hole punch for the notches; a light-tight box or tin to receive the cut strips.

The wet bench. Six 100 ml measuring cylinders in a rack; a tray large enough to stand them in as a water bath; three shallow trays long enough to lay a 135 mm strip flat, for the rinse, the fixer and the wash; a thermometer reading to 0.1 °C, checked against a reference by the balance and thermometer SOP; tongs, one pair per solution and a separate pair for fixer; a drying line with pegs; a lightbox; a flatbed scanner.

Estimated cost

££. The film is the recurring cost and the wedge is the one-off. A 30.5 m bulk tin yields around 225 strips of 135 mm, which is five times what the whole of Part IX consumes, and works out far cheaper per strip than four cassettes while removing cassette-to-cassette variation at the same time. The planner carries the numbers and the shopping list; this page carries only the band.

!The course has not verified a UK price for a 21-step wedge

Stouffer’s own product page specifies the parts but the course has not confirmed a current price or a United Kingdom supplier, so no figure appears here or in the planner for it. Budget for it as an instrument rather than a consumable: it is bought once and used for the rest of the course.

Estimated consumables cost

Nothing is weighed on this page, so the consumables are film, four solutions diluted from stock, and the sleeves. The wedge is an instrument, not a consumable, and the course has not verified a United Kingdom price for one.

Consumed	This session	Sourced price	Cost this session
Film, one emulsion batch	four 36-exposure cassettes, or one 30.5 m bulk tin	£6.37–£11.40 per one 35 mm roll, 36 exposures	£25.48–£45.60
D-76 stock, from Part VIII	250 mL, diluted 1+1 and discarded after one batch	Costed in Part VIII’s mixing lab	—
Rapid fixer concentrate	60 mL, to make 300 mL at 1+4	£21.05–£25.98 per 1 L of ammonium thiosulfate concentrate, diluted 1+4 for film	£1.26–£1.56
Wetting agent	1.5 mL, for 300 mL at 1+200	£28.70 per 1 L of concentrate, diluted 1+200	£0.04
Negative filing sheets or glassine envelopes	enough for 45 strips	None. A named price gap: sleeving that passes the Photographic Activity Test	—
Card label slips and opaque card	45 slips, one card strip	None. notebook carries a cost band and no dated figure	—
Water for the rinse and wash	about 3 L	Metered supply; the planner prices no water	—

The priced rows come to £26.79 to £47.20 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: 2 of the 7 rows carry no dated price, so they are counted as nothing here and are certainly not free. A priced entry is a dated range to plan against, never a quotation.

The film row prices four cassettes because that is the option with a dated figure; a 30.5 m bulk tin yields around 225 strips of 135 mm, is far cheaper per strip and removes cassette-to-cassette variation, and the price file carries no bulk-tin figure, so the cheaper route is the one this section cannot cost. That is worth saying plainly rather than pricing the option nobody should take.

Waste streams

Three, kept apart, each labelled per the container SOP and routed per the general waste SOP.

1. Spent developer, alkaline, carrying almost all of the metol and hydroquinone that were weighed out in Part VIII, because almost no silver was reduced. Its own container.
2. Spent fixer and the first rinse after it, which are silver-bearing and go to the silver stream. This is the stream that matters environmentally and it is the one people tip away.
3. Rinse and wash water. The rinse that follows the developer carries developer with it and goes with stream 1; the first change of wash water after fixing goes with stream 2, and the rest with the general stream.

Alternative route

The session as written needs total darkness, because a panchromatic film has no safelight. FOMA’s FOMAPAN 100 sheet says the same in one line: infrared light, or total darkness.

The orthochromatic route. Run the whole part on ILFORD ORTHO Plus instead. ILFORD state that its blue and green sensitivity allows handling under a deep red safelight, and recommend the ILFORD 906 filter with a 15 W bulb at not less than 1.2 m. Cutting, notching, loading and allocating strips then happen in dim red light rather than blind, which removes most of the mechanical risk on this page and a good deal of the error.

Two things it costs. The film is not panchromatic, so nothing learned about it transfers to how a panchromatic film handles a coloured subject — irrelevant here, because every exposure in Part IX is made through a neutral wedge from one lamp and each strip is compared only with its own batch. And the development times are ORTHO Plus’s own, from its own sheet, so the published D-76 figures used below do not apply and must be replaced before you start. Whichever film you choose, choose it for the whole part: changing film halfway ends the batch.

Preparation

1. Open the laboratory to the SOP. Check the thermometer against a reference and write down the offset.

2. Check the room is light-tight. Sit in it for five minutes with the light off and look for leaks around the door and the vent, as ILFORD’s leaflet directs. A leak you cannot see after thirty seconds is one you will see after five minutes, and it will fog the batch.

3. Set the lamp height and prove the geometry. One metre from lamp to film plane. Here is why that number and not a convenient 300 mm: illumination falls off across the strip as the inverse square of the distance and as the fourth power of the cosine of the angle, so at the far end of a 127 mm wedge the two effects together give

   (1000/1002)² × cos⁴(3.6°) ≈ 0.99

   Falloff at the end of a 127 mm strip, lamp at 1.00 m

   about one per cent, which is 0.005 log units, a thirtieth of a wedge step. Bring the lamp down to 300 mm and the same arithmetic gives 0.88 — twelve per cent, 0.06 log units, four tenths of a step, across a strip whose whole reading is a step number. The geometry is not a detail.

4. Lay out the dark bench exactly as it will be used: film at the left, jig in the middle, receiving tin at the right, and nothing else on it. Rehearse the cut once with the light on.

5. Mix the wet bench and bring everything to 20 °C in the water bath. D-76 1+1 is made just before use and discarded after one batch. Measure the clearing time on a film scrap in normal room light, and set the fixing time at twice it.

Procedure

Stage 1 — the pilot bracket, in darkness

6. Cut six strips at 135 mm on the jig. Give each one a datum notch: a single square nip at what will be the top-left corner, which tells you by touch which end is the head and which way the emulsion faces. Film curls towards its emulsion; feel for it.
7. Load one strip at a time into the rig, emulsion up, wedge on top emulsion-down, glass over both, the opaque card mask covering the last 10 mm of film beyond the wedge.
8. With the lamp burning and warmed, expose five strips at 2, 4, 8, 16 and 32 seconds by lifting and replacing the card shutter against the stopclock. Leave the sixth strip unexposed. Notch each with its own count of nips, 1 to 5, and the unexposed one with none.
9. Develop all six together in D-76 1+1 at 20 °C for 11 minutes — ILFORD’s published time for FP4 Plus at EI 125 in a spiral tank with intermittent agitation. Stop, fix for twice the clearing time, wash briefly and look at them wet.

Stage 2 — choosing the exposure

10. Pick the strip whose threshold sits around step 17, which puts the film’s usable scale in the middle of the wedge with room at both ends. If none does, correct the best one arithmetically.

    t₂ = t₁ × 10^(0.15 n P)

    Correcting an exposure by n wedge steps, allowing for reciprocity

    n is the number of steps you want the threshold to move, positive for more exposure, and P is the film’s reciprocity exponent — ILFORD publish 1.26 for FP4 Plus and 1.25 for ORTHO Plus, and state that exposures of one second or less need no compensation, for which P is simply 1. Moving two steps at one second or less multiplies the time by 2.0, one stop; moving two steps at eight seconds multiplies it by 10^(0.30 × 1.26) = 2.4. That difference is the whole of why the bracket above is not a series of exact stops.

11. Write the chosen time in the notebook as the exposure batch, along with the lamp, its distance, the wedge’s part number, the film and its emulsion batch, and the date.

Stage 3 — the batch, in darkness

12. Cut the remainder of the film into 135 mm strips on the jig, datum-notching each one, and put them in the light-tight tin as you go. Expect ten or eleven per 36-exposure cassette; a 30.5 m bulk tin gives around 225.
13. Do not give them identity codes now. Until a strip is committed to a developer it is interchangeable with every other strip in the tin, and coding forty of them by touch would add forty chances of error and buy nothing. The identity nips go on at allocation, in the dark, at the start of each experiment, when there are only six or eight to distinguish.
14. Expose every strip at the chosen time, in the rig, without changing anything. Work steadily; the lamp stays on throughout so there is no warm-up to drift.
15. Set aside four strips for today: three exposed at the start of the run and one exposed last. Return the rest to the tin, close it, label it with the batch name and the date, and put it in the dark and cool.

Stage 4 — the control set

16. Develop the four strips together in D-76 1+1 at 20 °C for 11 minutes, each in its own 100 ml measuring cylinder standing in the water bath, with at least 80 ml of solution — enough to stand about 150 mm deep and cover a 135 mm strip with room to spare. Check the depth with a scrap and water before you commit developer to it.

17. Agitation script, written down and identical for every strip in the part: lower the strip in and move it gently up and down for the first 30 seconds, then lift, drain for two seconds and re-immerse once at the start of every subsequent minute. Stagger the four starts by 30 seconds so the lifts do not collide.

    📓This is not the agitation the published time assumes

    ILFORD’s 11 minutes is for a spiral tank with intermittent inversion agitation, and they add that continuous agitation, as in a dish, should shorten spiral-tank times by up to 15 per cent. A strip lifted in a cylinder is somewhere between the two, and the course has not measured where.

    That does not spoil anything, because every strip in Part IX gets the same script and the comparison is between strips. It does mean the control set is a first datum and not a correct development, and the notebook says so. Write the script out in full; a time without an agitation scheme is not a process.

18. Keep the temperature within 0.3 °C for the whole eleven minutes. That is not a round number chosen for tidiness: Kodak’s process-control publication states that a developer temperature varying by more than 0.3 °C affects process control and image quality, and the ILFORD time-temperature chart puts one degree near 20 °C at about nine per cent of the development time.

19. Rinse for one minute in two changes of plain water, fix for twice the clearing time, wash for 5 to 10 minutes in water within 5 °C of the developer, final-rinse in wetting agent at 1+200, and hang the four strips to dry in still, dust-free air. Do not squeegee a test strip: a drying mark on a step is read as density.

    📓Why Part IX rinses in water instead of using a stop bath

    Two of the developers coming later in the part are alkaline with sodium carbonate, and carbonate carried into an acid bath makes carbon dioxide inside a warm swollen gelatin layer; Part VIII draws what happens next. Treating those strips differently from the rest would put a second variable into the comparison, so every strip in Part IX gets the same plain water rinse, starting with this control set.

    The cost is named by ILFORD rather than hidden: a water rinse may be substituted for a stop bath but increases the risk of processing marks and stains. That is the trade — a small uniform risk of marks on every strip, against a large risk of blisters on a few and a confounded experiment either way.

20. When they are bone dry — not before — read them.

Expected observations

On the pilot bracket. Five strips forming an obvious progression, each one’s threshold a step or two further along than the last. If two adjacent members of the bracket look identical, suspect the shutter timing rather than the film.

On the control strips. A wedge image with a clear dense end, a run of separable greys, and a foot that fades into the masked patch. The masked patch itself should be very slightly denser than clear film base, and that difference is the chemical fog.

Between the control strips. They should look the same. Reading them will show that they are not quite, and by how much is the number this session exists to produce.

On the strip exposed last. It should match the three exposed first. If it does not, the lamp, the rig or the operator drifted during the run, and the whole batch inherits it.

What is happening chemically

Nothing new. This session is Part VIII’s chemistry run under a stopwatch, and the point of naming it again is to see which part of it the control is actually holding still.

The developer is an electron donor whose potential is enough to reduce silver ions at a latent image speck and not, in eleven minutes, on a bare crystal. Metol and hydroquinone act together at more than the sum of their separate rates — the superadditivity Part VIII spends a page on — with the borax holding the pH where that pairing works and the hundred grams of sulfite per litre of stock doing three jobs at once: taking the oxygen that would otherwise reach the agents, providing most of the alkalinity, and dissolving a little silver bromide as a solvent.

Dilute that stock 1+1 and every one of those is halved. There is half the agent, half the buffer, half the solvent and half the reserve against exhaustion, which is why Kodak’s own sheet says a 1+1 working solution is made just before use, used once and neither reused nor replenished. The control developer is therefore not “D-76” in general; it is one bottle, at one dilution, on one day, and the version number on it is what makes that statement checkable.

Two things are deliberately absent. There is no bromide in D-76 and none is added here, so the restrainer is whatever the film releases into the eighty millilitres as it develops — which is a real effect, is the reason the volume per strip is specified, and is the subject of an experiment two pages on. And there is no added alkali beyond the borax, so the working pH sits where Part VIII computes it rather than where a carbonate would put it.

⚗What the control represents, exactly

A control is not “a good negative”. It is a statement of the form: this film, from this emulsion batch, given this exposure from this geometry, developed in this version of this formula at this dilution, for this time, at this temperature, with this agitation, produced this threshold and this scale length.

Every clause is load-bearing. Drop the emulsion batch and a later disagreement might be the film. Drop the version number and it might be the mix. Drop the agitation and it might be your wrist. The reason the notebook fields look excessive is that a control with a missing clause is not a control, and you will not find out which clause you needed until the day the numbers disagree.

Data to record

Copy this into the notebook before the session, not after it.

Session header. Date; who; room temperature at start and end; the light and the lightbox you read by; every instrument used with its checked offset; the wash water temperature.

Exposure batch block, which every strip in Part IX will refer back to by name: film, format, emulsion batch number; lamp type and power; lamp-to-film distance, measured; wedge part number and whether it is a calibrated part; the pilot bracket times and what each one gave; the chosen exposure time; the number of strips cut and the number exposed; date and time of the run.

Developer block. The formula version of the D-76 stock, its mixing date, its measured pH and the temperature of that measurement; the dilution; the volume per cylinder; the time, the temperature at start, middle and end, and the agitation script in words.

Readings, one row per strip. Notch code; threshold step; scale length in steps; a description of the masked patch against clear base; matched densities if you took them; scanner code values with every scan setting written out.

Deviations. Everything that went differently from the plan. A strip dropped, a lift missed, a cylinder knocked, a thermometer found reading 0.4 °C low at the end.

Analysis

1. Read the four control strips blind. Have the notch codes assigned to random reading numbers by a shuffled set of cards, read all four in one sitting in random order, and only then open the key.
2. Tabulate threshold step and scale length for each. Take the spread — the difference between highest and lowest — for each quantity.
3. State your resolution limit. That spread, in steps, is the smallest difference the rest of Part IX may report as real. Write it at the front of the notebook where the next four sessions will see it. A spread of one step is a good rig. A spread of two steps is a stop of exposure and needs fixing before anything else is run.
4. Compare the strip exposed last with the three exposed first. If it sits inside the spread, the run was stable and the batch is one batch. If it does not, say so in the batch block, because every later session is about to assume it.
5. Read base plus fog on the masked patch of each strip against a piece of clear, fixed, unexposed film from the same batch. You cannot put a number on it without a densitometer; you can rank it and describe it, and you can scan it, and both are worth doing because this is the floor every later fog comparison moves against.
6. Convert scale length to an average gradient, and then distrust it. Ḡ = (D_max − D_min) / (0.15 × S) requires two densities you do not have. Compute it if you took matched densities; otherwise record S and leave the gradient alone, as the design lesson sets out.
7. Scan all four strips and the wedge in one pass with every automatic function off, and plot the wedge’s code values against its nominal densities. That curve is your scanner’s response, measured on the day, and it is the only thing that tells you how far up the density scale its numbers stay usable.

Troubleshooting

What you see	Likely cause	What to do
Every pilot strip is black to the last step	The lamp is far brighter than the bracket assumed	Halve the shortest time and re-bracket, or raise the lamp — but if you raise it, the geometry has changed and the falloff arithmetic must be redone
Every pilot strip is nearly blank	Too little light, or the film is fogged out at the other end	Check the lamp is actually reaching the film; then re-bracket upwards, remembering that the time factor for a stop is 2.4 and not 2 above one second
Strips fogged evenly, including the masked patch	A light leak, or the tin is not light-tight, or a safelight is on	Re-run the five-minute leak check. The masked patch is the diagnostic: it saw no lamp, so density on it is fog and not exposure
The masked patch is fogged but the film edges are clear	The mask moved during the exposure	Tape the mask to the glass rather than laying it on the film
The four control strips disagree by two steps or more	Shutter timing, film not flat against the wedge, or an inconsistent read	Check flatness first — it is the commonest and the cheapest to fix. Then time the shutter against the clock ten times and look at the spread
Strips show pale streaks running from the steps	Uneven agitation in the cylinder, or too little solution	Check the depth covers the strip with room; lift and drain to a consistent count
A milky or violet cast on the dried strips	Under-fixing, or an exhausted bath	Re-fix in fresh fixer. Do not archive an under-fixed strip: Part XXVII will read it in a year and by then the damage will be its own
Drying marks read as density	Squeegeed, or the wetting agent was too strong or too weak	Re-wash and re-dry without touching the surface. ILFORD warn that both too little and too much wetting agent give uneven drying

Clean-up

Pour each cylinder into its own waste container as you finish with it, rinse it twice into the same container and only then into the sink. Wash and dry the cylinders, the rack, the tray and the tongs, keeping developer and fixer utensils separate — Kodak’s troubleshooting publication names mixing equipment that has not been thoroughly cleaned as a cause of solution contamination, and a developer contaminated with fixer is a batch lost. Throw the gloves away. Close the laboratory to the SOP.

Storage

The unexposed film, if any is left, goes back in its packaging, cool and dark, with the batch number still legible.

The exposed, undeveloped strips go into the labelled light-tight tin. This is where the part’s one unavoidable compromise lives: a strip exposed today and developed in three weeks has had three weeks of latent image keeping, and it is not the same strip as one developed this evening. The course does not pretend otherwise. The mitigation is structural, and every later page uses it: each session develops a shared reference strip from this same batch under this same standard condition, so drift is measured rather than assumed. Store the tin cool and dry, and run the sessions as close together as you can.

The developed control strips are the first entries in the archive, and the archive is the deliverable of the whole part.

A sleeve pocket, and what has to be written on the slip inside it

1. 1Batch — film, emulsion batch, lamp, distance, exposure time, wedge, date
2. 2Strip — notch code and position in the batch
3. 3Arm and cell — which experiment, which condition, in words
4. 4Developer — formula version, dilution, addition in g/L, measured pH and its temperature
5. 5Development — time, temperature at start/middle/end, agitation script, vessel, volume
6. 6Finish — fixer and dilution, clearing time, fixing time, wash, drying
7. 7Readings — threshold step, scale length, base plus fog, and the date read
8. 8Provenance — notebook page and initials

The test the label has to pass: could somebody holding only this sleeve repeat the strip? Part XXVII will be that somebody, and it will not have you to ask.

Disposal considerations

Three containers, kept separate, each labelled with its contents and the date.

The developer waste carries almost all of the metol and hydroquinone it was mixed from, because a handful of strips reduces very little silver. Both agents are notified as very toxic to aquatic life with long-lasting effects. ILFORD’s advice to domestic users in the United Kingdom is to bottle each waste chemical separately, label it, and take it to a Household Waste and Recycling Centre.

The fixer and its first rinse are silver-bearing and go to the silver stream, per the silver-bearing waste SOP. Combining them with the developer gains nothing and spoils the recovery.

The rinse and the wash water are split: the rinse that follows the developer carries developer and goes with the developer container, and the first change of wash water after fixing carries fixer and goes with the silver stream. The rest goes with the general stream.

The route is not the course’s to decide. The disposal page sets out why the answer is jurisdictional and differs between authorities within one country. Check your local regulations; they govern.

Questions

1. Your control set gives thresholds of 17, 17, 18 and 17, and the strip exposed last reads 15. What has happened, and which of the four numbers is the one you should not average away?
2. You have 45 strips and the part needs about 41. Where would you spend a surplus of four, and why is the answer not “one more replicate in each cell”?
3. The masked patch on one strip is noticeably denser than on the other three, but the wedge image looks identical. Name two causes and say which reading would separate them.
4. A friend suggests halving the lamp distance to shorten the exposure and reduce reciprocity error. Work out what that does to the evenness across the strip, and say whether the trade is worth taking.
5. You cut the strips at 130 mm instead of 135 mm and the wedge overhangs the film by 3 mm at the tail. Which reading is affected, and is the batch still usable?
6. Why does this page insist the strips are read dry, when a wet strip is easier to handle and the session is already three hours long?

Further experiments

Time the shutter. Lift and replace the card ten times against the stopclock at your chosen exposure and take the spread. That number, converted through 10^(0.15 n P), tells you how many wedge steps of scatter your hand contributes, and it is very often the largest single term in the batch’s uncertainty.

Map the illumination. Expose four strips with the wedge placed at the centre, the two ends and one corner of the baseboard, all at the same time, and compare the thresholds. If they differ, the rig has a position dependence and every strip must be loaded in the same place.

A latent-image keeping series. Set aside five strips from this batch and develop one on day 0, one at a week, one at a month, one at three months and one at six, all under the standard condition. Nobody has published this for your film, your storage and your rig, the whole of Part XXVII’s argument rests on the answer being small, and five strips is a cheap way to find out whether it is.

Two wedges, one strip. If you can borrow a second wedge, expose one strip through each in turn on opposite halves and see whether the two nominal 0.15 increments agree. It is the only calibration check available without an instrument.

Check your understanding

Question 1. Why is the identity code applied to a strip at allocation, in the dark at the start of an experiment, rather than at cutting time?

• Because the notches would be damaged in storage
• Because until a strip meets a developer it is interchangeable with every other strip in the tin, so coding forty of them by touch adds forty chances of error and distinguishes nothing that needs distinguishing
• Because the code depends on the exposure time
• Because notching before development fogs the film at the cut edge

Show the answer and why

Answer: Because until a strip meets a developer it is interchangeable with every other strip in the tin, so coding forty of them by touch adds forty chances of error and distinguishes nothing that needs distinguishing

The design principle is that a label should carry only the information that exists at the moment it is written. At cutting time the only fact about a strip that matters is which end is the head and which way the emulsion faces, and the single datum notch records exactly that. Identity — this is the carbonate cell, that is the control — comes into existence when the strip is committed to a vessel, and at that moment there are six or eight to tell apart rather than forty, so a count of one to five nips does the whole job.

Question 2. The pilot bracket runs 2, 4, 8, 16 and 32 seconds. Why are those not five one-stop steps for FP4 Plus?

• Because the lamp is not stable enough for exact doublings
• Because above one second the reciprocity law fails, and ILFORD give corrected time as metered time raised to the power 1.26, so a doubling of the actual time is worth about 0.24 log units of effective exposure rather than 0.30
• Because the wedge attenuates the light unevenly across its length
• Because the film’s speed changes with exposure time

Show the answer and why

Answer: Because above one second the reciprocity law fails, and ILFORD give corrected time as metered time raised to the power 1.26, so a doubling of the actual time is worth about 0.24 log units of effective exposure rather than 0.30

ILFORD publish the relation as corrected time equals metered time raised to the exponent P, with 1.26 for FP4 Plus, and state that exposures of one second or less need no compensation. Inverting it, a doubling of actual time delivers an effective exposure factor of 2 to the power one over 1.26, about 1.71, which is 0.234 log units — roughly 1.6 wedge steps rather than 2. The practical consequence is in the correction formula: to move the threshold two steps at an eight-second exposure the time is multiplied by 2.4, not by 2.

Question 3. Why does each strip carry its own masked patch instead of the session using one unexposed strip as a shared base-plus-fog reference?

• Because it saves a strip
• Because base plus fog depends on the developer as well as the film, so a shared reference would import one cell’s developer into another cell’s reading — and fog is exactly what several experiments in the part are trying to measure
• Because an unexposed strip would be lost among the others
• Because the masked patch is easier to scan

Show the answer and why

Answer: Because base plus fog depends on the developer as well as the film, so a shared reference would import one cell’s developer into another cell’s reading — and fog is exactly what several experiments in the part are trying to measure

The floor is not a property of the film alone. Chemical fog is made by the developer — a higher pH, a longer time or no restrainer each raise it — so the carbonate cell and the bromide cell have genuinely different floors, and the whole point of the alkali and restrainer experiment is to see them move. A patch that went through the same 80 ml of the same developer as the wedge image beside it is the only floor that belongs to that reading. It also happens to be free: the mask costs a strip of card.

Question 4. ILFORD’s 11 minutes assumes a spiral tank with intermittent inversion agitation, and this page develops strips in a cylinder. Does that invalidate the control set?

• Yes, and a spiral tank must be used instead
• No, provided the same written script is used for every strip in the part and the control is treated as a first datum rather than a correct development, because every conclusion in Part IX is a comparison between strips of one batch
• No, because agitation does not affect development
• Yes, unless the time is shortened by 15 per cent

Show the answer and why

Answer: No, provided the same written script is used for every strip in the part and the control is treated as a first datum rather than a correct development, because every conclusion in Part IX is a comparison between strips of one batch

Agitation is one of the four factors Kodak’s workbook names as affecting contrast index, and ILFORD put the difference between intermittent and continuous agitation at up to 15 per cent of the time, so it is a large effect and cannot be waved away. What rescues the design is that it is held constant: an effect common to every strip cancels out of every comparison between strips. What it costs is the right to compare these strips with a manufacturer’s published curve, which is why the notebook records the script in words and the page calls the result a datum rather than a correct development.

Question 5. Your four control strips read thresholds of 16, 17, 18 and 17. What is the resolution limit, and what does it forbid?

• One step, because most of them agree
• Two steps, the full spread, which forbids reporting any experimental difference of one or two steps as a real effect until the rig is improved
• Half a step, because the mean is 17
• There is no limit until a densitometer is available

Show the answer and why

Answer: Two steps, the full spread, which forbids reporting any experimental difference of one or two steps as a real effect until the rig is improved

The spread across identically treated strips is the honest floor, and it is 18 minus 16, two steps. Two steps is 0.30 log units of exposure — a full stop — and it is larger than most of what Part IX sets out to measure, since an 8 per cent contrast change corresponds to about one step. Averaging to 17 and quoting a tighter figure would be borrowing precision the process has not demonstrated. The useful response is diagnostic rather than statistical: look at film flatness against the wedge, then shutter timing, then the reading method, and re-run the control set before an experiment is built on it.

Question 6. Why does the page specify a lamp distance of 1.00 m rather than a more convenient 300 mm?

• To keep the lamp away from the wet bench
• Because illumination falls off across the strip with the inverse square of distance and the fourth power of the cosine of the angle: at 1 m that is about 1 per cent across a 127 mm wedge, a thirtieth of a step, and at 300 mm it is about 12 per cent, four tenths of a step
• Because the lamp would overheat the film at 300 mm
• Because a longer exposure is always more repeatable

Show the answer and why

Answer: Because illumination falls off across the strip with the inverse square of distance and the fourth power of the cosine of the angle: at 1 m that is about 1 per cent across a 127 mm wedge, a thirtieth of a step, and at 300 mm it is about 12 per cent, four tenths of a step

The two geometric effects compound, and the arithmetic decides the rig. At one metre the far end of the wedge receives about 99 per cent of what the near end receives, which is 0.005 log units and disappears beneath every other error in the session. At 300 mm the same calculation gives 0.88, about 0.06 log units — four tenths of a wedge step of built-in gradient, running along the strip in the same direction as the wedge itself and therefore impossible to separate from it by looking. Electrical separation from the wet bench is a real requirement too, but it is a different one and it does not set the distance.

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