Lab: Dodging, Burning, Edge Work and Local Contrast

The previous lab produced a number. This one produces a print, and the difference between them is everything a printer does with their hands in the three minutes after the timer starts.

Local control is described as feel, as touch, the part that cannot be taught — and printers who work that way cannot say afterwards what they did. Almost none of it is ineffable. The softness of the edge a card leaves is a length you can calculate before you cut it; the size of a burn is a ratio; what a dodge costs in the shadows follows from the paper’s curve. Three hours, a dozen sheets and one negative, at the end of which you have a print and, more usefully, a printing map that will produce it again.

Purpose

To take one negative from the base exposure established in the previous lab to a finished interpretation, using dodging, burning, edge work and locally applied contrast; to express every move as a fraction of a stop rather than a number of seconds; to predict the softness of every edge from the enlarger’s own geometry before making it; and to finish with a map complete enough that the same print can be made from it three weeks later. It also settles, by measurement rather than assertion, how much of what printers call feathering is geometry and how much is the hand.

Learning objectives

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

• Derive the width of the soft edge a tool leaves from the aperture, the magnification and the tool’s height, and choose that height to get the edge you want.
• Say in numbers why a still tool leaves a boundary the eye finds at once, and how far and how fast a tool must move to hide it.
• Convert any local move into stops, add two burns on one area, and explain why half a stop plus half a stop is not one stop.
• Say what a dodge does to the local contrast of the area it lightens and a burn to the area it darkens, from the shape of the paper’s curve.
• Give a burn through a different filter from the rest of the print, and record it reproducibly.
• Separate an edge burn that is a decision from one that is a mannerism, and from the corner falloff your enlarger gave you for nothing.
• Run a printing session that converges, and write a map a stranger could follow.

Prerequisites

• Test strips, base exposure and the print’s black point, which produced the base exposure everything here is measured from and the ring-around you will judge against.
• Contrast filtration and split-grade printing, which owns what a filter does and establishes that two exposures on one sheet add.
• Reading the negative and making the work print, which produced the marked-up work print that is tonight’s brief.
• F-stop timing and the mathematics of print exposure, which owns the arithmetic of a burn and a dodge.
• Enlarger optics and design for the effective aperture and the corner falloff, and the contact printing frame for the penumbra relation this page re-applies.

Safety classification

Level A throughout, for the same reasons as the previous lab: three baths at tray dilution, at room temperature, nothing weighed, heated or mixed from powder. What differs tonight is the duration and the movement — three hours is long enough for tiredness to become the principal hazard, and the point of the session is that your hands are in the light path in the dark.

• The developer is alkaline and, if it is D-72 or another metol–hydroquinone paper developer, contains metol and hydroquinone, both skin sensitisers and eye hazards. Gloves and eye protection whenever a solution is handled; prints lifted with tongs.
• The enlarger is a mains appliance and you will be reaching under it in the dark, repeatedly. A cable across the bench, an open filter drawer, a foot switch trailing across the floor — each is a thing to catch a wrist on at the moment your eyes are on the easel.
• Wet hands under a hot lamp. A tungsten or halogen head runs hot enough to burn, and every dodge close to the lens brings a gloved hand wet with developer within centimetres of it. Find the lamphouse by touch before the lights go off.

What is not a hazard here, and why. There is no dust exposure: nothing is weighed and no jar of powder opened, so the argument that raises the developer-mixing lab to Level B is absent with the operation that created it. There is no sulfur dioxide route, because the acid stop and the sulfite-bearing developer meet nowhere. There is no concentrated silver: it is locked in hardened gelatin or dissolved in the fixer at an amateur bath’s concentrations. The same substances as dry powders are a different assessment entirely, and Part II makes it.

Hazards

Hazard	Where it arises	Control
Skin sensitisation from metol and hydroquinone	Developer tray; wet prints handled by hand	Nitrile gloves; tongs; a glove contaminated inside changed, not rinsed
Eye irritation from an alkaline splash	Pouring; rocking a dish for three hours	Eye protection from first pour to last rinse; rinse a splash at once and keep rinsing
Mains equipment and moving hands in darkness	Reaching under the lens with the lights off	Cables dressed away from the reach path; wet and dry sides separated; hands dried before any switch
Hot lamphouse	Dodging close to the lens on a tungsten or halogen head	Locate it by touch with the lights on; keep the dodger’s wire long enough that the hand stays low
Fatigue, and the errors it causes	The third hour, when prints are judged by hope	A break with the lights on at ninety minutes; the session ends when the map is written
Slips and knocks in near darkness	Carrying wet prints to a viewing light and back	Floor cleared with the lights on; one route, walked in advance
Blade injury	Cutting cards and apertures	Cut in the light, on a mat, free hand behind the blade line
Aquatic toxicity of every spent bath	Clean-up	Collect separately, never a drain; see Disposal considerations

Required PPE

Nitrile gloves for the wet half of the bench, changed when contaminated inside. Eye protection with side shields whenever a solution is poured or a dish rocked. One pair of tongs per bath, which ILFORD ask for explicitly, because a trace of fixer carried back into the developer gives inconsistent results or blank prints. Respiratory protection is not among the controls here for a specific reason rather than a reassuring one: nothing is a powder and nothing is heated, so the airborne route that justifies a mask on the mixing page is absent.

One item is unusual enough to name. The glove on your dodging hand is a printing tool as well as a control: a dark nitrile glove is a poor reflector, a pale one under the lens bounces light back onto the easel and lifts the shadow you were protecting. Use the same glove all evening.

Ventilation

An openable window or an extractor giving a through draught, checked with the ventilation check before the lights go off. The airflow is not a vapour control — no bath is heated, no solvent is present, and the most volatile thing on the bench is water. It keeps a closed room tolerable for three hours, which is what stops the last three decisions being made badly.

Materials

Item	Quantity	Note
Variable-contrast paper, 8 × 10 in, the final print’s surface and base	14 sheets	One cut into four strips, ten whole prints, three spare
The negative from the previous two sessions	1	Same frame, carrier and orientation
The marked-up work print	1	Tonight’s brief
Developer at the dilution your source gives	1 L working	Same developer, dilution and age bracket as the session that set the base
Stop bath concentrate	50 mL	1+19, 1 L working
Rapid fixer concentrate	200 mL	1+4, 1 L working, non-hardening
Wetting agent	5 mL	1+200 final rinse
Stiff opaque card, A4 or larger, matt black one side	3 sheets	One with its factory-straight edge, one torn, one for cutting apertures
Stiff wire, about 1.5 mm, 300 mm long	2	Dodger handles, black or blackened
Soft pencil and a fine permanent marker	1 each	Every print numbered on the back before it is wet
Ruler and a cutting mat	1 each	Tool geometry is measured, not judged

The tools are made in the light, before the session, to sizes you calculated; stage 2 gives the arithmetic, and a dodger cut to look about right is why a first attempt leaves a patch.

Chemicals

Nothing is mixed from powder on this page; the working baths come from stock or concentrate. The quantities below are what is in the tray for the D-72 route at 1+4 in 1 L of working solution, not what you weigh.

Chemical	Quantity in the tray	Form and role
Metol	0.62 g	Dissolved; the primary developing agent carried in by 200 mL of D-72 stock
Hydroquinone	2.44 g	Dissolved; the contrast agent of the same stock
Sodium sulfite	9.0 g	Dissolved, anhydrous; preservative
Sodium carbonate	13.5 g	Dissolved, anhydrous; alkali
Potassium bromide	0.38 g	Dissolved; restrainer
Citric acid	50 mL of concentrate	Made up as stop bath, 1+19, 1 L in the tray
Ammonium thiosulfate	200 mL of concentrate	Made up as rapid fixer, 1+4, 1 L in the tray, non-hardening

If you use a bought paper developer its composition is not published and this table does not describe it: use the maker’s dilution and time, record the product and batch, and note on the map that the developer is proprietary.

Equipment

Enlarger, aligned, warmed and with its illumination mapped, from the commissioning experiment — and tonight its falloff figures matter as much as its alignment, for reasons stage 6 gives. Timer capable of adding a fraction of a stop to a remembered base, from Part XVII. Easel. Full filter set or colour head, filters clean, because ILFORD state that marks from dust, rough handling or fingers reduce print contrast and degrade the image and tonight they are changed mid-exposure with wet hands nearby. Fog-tested safelight. Four dishes and a pair of tongs each. Thermometer. Drying rack. A viewing light, the same one every session, at the distance you judge finished prints from, with the previous lab’s dry ring-around beside it.

Estimated cost

Band ££. No capital is bought tonight: the enlarger, timer and dishes belong to Parts XVI and XVII, the developer to Part XVIII, and the tools are card and wire. The band records that the session is consumed rather than kept — fourteen sheets and three tray-fulls per negative. The planner holds the dated figures and the gaps.

Estimated consumables cost

Consumed	This session	Sourced price	Cost this session
RC paper, 8 × 10 in, variable contrast	14 sheets	£33.50 for 25 sheets to £96.18 for 100	£13.44 to £18.76
Fibre-base paper, if that is your paper	the same 14 sheets	£47.04 for 25 sheets to £150.28 for 100	£21.04 to £26.34
Paper developer concentrate or stock	200 mL of D-72 stock, or 100 mL of concentrate for 1 L at 1+9	£10.52 per 500 mL to £20.03 per 1 L, bought	£2.00 to £2.10
Stop bath concentrate	50 mL, for 1 L at 1+19	£10.66 to £12.18 per 500 mL	£1.07 to £1.22
Rapid fixer concentrate	200 mL, for 1 L at 1+4	£21.05 to £25.98 per 1 L	£4.21 to £5.20
Wetting agent for the final rinse	5 mL, for 1 L at 1+200	£28.70 per 1 L	about £0.14
Card and wire for the tools	about half an A4 sheet and 600 mm of wire	Household material; the price file holds no listing	—
Contrast filters, if you do not own a set	not consumed	None. Yellow, orange and red contrast filters are one of the gaps the price file names	—

The rows carrying numbers total about £21 to £27 on the resin-coated route, a floor rather than a total: high in one direction, because the stop and the fixer are charged whole to one evening while ILFORD state both can be used for more than one printing session; low in another, because the filter set has no sourced price in this course. The fibre row is an alternative to the RC row and not an addition to it, and taking it raises the paper line by about £8. Equipment is not in the table, because an enlarger is not consumed.

Fourteen sheets is the honest figure. A local-control session does not make one print; it makes a sequence differing by one decision each, and a marked-up work print usually carries six to ten decisions. Budget for one print and you will combine changes to save paper, which is the failure stage 8 exists to prevent.

Waste streams

Three, and they stay apart. Alkaline developer, about 1 L, carrying negligible silver on Kodak’s own figures and governed by its pH and aquatic classification. Acid stop, 1 L, in its own container. Silver-bearing: the spent fixer with the first wash, under the silver-bearing waste procedure. Solids bagged, because a processed print carries silver in hardened gelatin. All of it sits under the disposal caveat; check your local regulations.

Alternative route

The exposing half of this session needs a room that can be made dark, and there is no substitute. ILFORD are encouraging about how little that takes: print-making needs “just a room that can be blacked out”, and no running water, because washing happens in daylight.

Without an enlarger, almost all of this transfers to Part XVI’s contact frame, and with a lineage, since everything Abney describes in 1905 is contact work under a printing frame. What changes is the geometry: an enlarger’s source is a small aperture far away, so edges are hard and you soften them deliberately, while a contact frame’s is usually large and close, so everything is soft whether you wanted it or not and the tool has to sit on the glass. Run the stage 2 arithmetic for your own light box before cutting anything, because the numbers differ by an order of magnitude.

Without a timer that adds fractions of a stop, do the arithmetic on paper before the lights go off and run the moves on any clock with a second hand, writing the seconds on the map beside the stops they represent. The stops are what you keep; the seconds are tonight’s translation.

Without a second filter, everything except stage 7 survives and local contrast has to come from the size and placement of the burn and from the choice of paper. Record that the column was unavailable rather than unused.

Without any darkened space at all, the exposing work cannot be run and the substitute is not a smaller version of it. It is the arithmetic and the design: compute the penumbra for each intended tool at three heights on your own enlarger’s numbers, cut the tools, convert every marked area into a move in stops with its filter, and write the map with the local-move column complete and the base exposure blank. What you must not do is fill in results you did not observe, because a later reader cannot tell an estimate from a measurement once both are in ink.

Preparation

All of this with the lights on, and none of it is optional.

1. Switch the enlarger head on first. Part XVI’s warm-up rule matters more tonight than during the test strips, because tonight’s prints are compared with each other: a first print made cold and a fourth made warm can differ by a tenth of a stop for reasons unconnected with any decision in between, which is session exposure drift masquerading as progress.
2. Set the geometry to the numbers already on the map — lens, working aperture, magnification, easel blades — and focus at full aperture before stopping down. If the magnification moved, nothing tonight is comparable with the previous session, because the base exposure was measured at one.
3. Confirm the base exposure on one whole sheet, processed at the session’s fixed time, temperature and agitation, and dried. If it does not match the previous session’s sheet, find out why first: every move tonight is a fraction of that number.
4. Lay the marked-up work print beside the easel and read your notes back. Each mark becomes one map row before any paper is exposed: an area, a direction, a first estimate in stops and a filter. Estimates are allowed here; guesses in the results column later are not.
5. Cut the tools to the sizes stage 2 gives, on a mat, with a ruler, and blacken every shiny edge: a card cut from a glossy box lid reflects enough light to fog the area it was protecting.
6. Fill four dishes and bring the baths to temperature — 20 °C for the developer on both ILFORD paper sheets, 18 to 24 °C for stop and fixer — then fix the development time and agitation to the ones the base exposure was established under. ILFORD give one minute at 20 °C for MULTIGRADE RC papers in MULTIGRADE developer at 1+9 and 1:30 to 3:00 for MULTIGRADE FB CLASSIC, noting that FB development extends to six minutes without noticeable change in contrast or fog. A range is not permission to vary within it.
7. Clear the reach path with the lights on, and walk the route to the viewing light once. Put your hand where the dodger will go and find out now whether your wrist meets the filter drawer, the lamphouse or a cable.
8. Start the map sheet and number it before the room goes dark. A map that acquires its version numbers afterwards from memory is a diary.

📓The one field to fill in before anything else

The map’s intention field was written two lessons ago: one sentence saying what a viewer should notice. Read it before you start. Every decision tonight is a trade — a burn that holds the eye in the frame costs a tone somewhere — and a trade cannot be judged without a criterion. A printer who cannot say what the print is for makes a different print every time and believes each one is an improvement.

Procedure

Stage 1 — the tools, and what each one is actually for

ILFORD describe the whole apparatus in one clause: “using your hands or pieces of card to hold back light from or give extra light to selected areas of your print”. That is the complete inventory; what follows is why each shape exists.

Five tools, and the property of each that does the work

1. 1Card with a straight cut edge — A boundary that stays straight. Horizons, window reveals, the top of a wall
2. 2Card with a torn edge — The tear is 2 to 5 mm deep, so it softens the boundary along its length independently of the lens geometry. Tear it towards you so the fibres lift away from the paper
3. 3Aperture cut in card — A burn landing inside the picture with the rest of the sheet shielded. Cut it smaller than the area: the shadow of the card, and therefore the hole, is magnified
4. 4Dodger: a small blade on a long wire — The blade withholds; the wire does not, because at that height its own penumbra is wider than the wire
5. 5Two cards making an adjustable slot — A band of any width, from a slit to half the frame, without cutting a new tool

Plan views, drawn to show the shapes rather than to scale. The sizes that matter are computed in stage 2 from your own enlarger, not copied from a drawing.

Your hands are the best two tools you own, being infinitely adjustable and already attached to the moving arm: cupped they make a soft oval aperture, edge-on a straight-ish line, fingers spread a graded mask no card reproduces. What they cannot do is repeat, so the working method is to find the move with the hands and then cut a card that does the same thing.

The torn edge does something the geometry cannot. Every other softening here comes from the lens aperture’s angular size, which stage 2 shows is small; a tear lifts the card’s fibres out of the plane over two to five millimetres, so the shadow’s edge is ragged over that distance whatever the enlarger is doing. Wall’s 1912 dictionary reaches the same solution for vignetting, preferring sheet lead or tinfoil with the opening cut and its edges “slightly turned up” or serrated “so as to soften the outline”.

Stage 2 — how soft an edge will be, before you cut anything

This is the part usually left to feel, and it need not be. Two results the course already has are enough. From Part XVI’s contact frame, a source of width S at a distance D above an opaque edge casts, on a surface a gap g below that edge, a partial shadow of width S × g ÷ D — Ware’s blur equals gap times aspect value, from similar triangles. From Part XVI’s enlarger optics, the aperture diameter is S = f ÷ N and the lens sits at v = f(1 + m) above the paper.

Under an enlarger the tool may be a third of the way up to the lens rather than a hair’s breadth above the paper, so the aperture-to-tool distance is v − g and the relation must keep that distinction:

b = S × g ÷ (v − g)

Width of the soft edge a tool leaves

b is the width of the partial shadow on the paper, S the working aperture’s diameter, g the tool’s height and v the lens-to-paper distance. Substituting the two Part XVI relations gives the form worth remembering:

b = g ÷ (N(1 + m) − N g ÷ f)

The same thing, in the quantities marked on the enlarger

and for a tool low enough that g is small compared with v, that collapses to something you can do in your head: the softness of the edge is the tool’s height divided by the effective f-number, N(1 + m) — the same effective aperture Part XVI derived, and the one Rodenstock confirm in stating that a lens focused at about 1 to 1 has an effective aperture approximately two stops smaller than the nominal one.

Where the softness of an edge comes from

1. 1The working aperture, diameter S = f / N — The only source in the room. It is small and far away, which is why edges under an enlarger are hard by default
2. 2The tool, at height g above the paper — The single number you control at the easel. Everything else is set by the lens and the enlargement
3. 3Umbra: the aperture is completely hidden — Full shielding. A dodge here withholds the whole base exposure
4. 4Penumbra of width b, where part of the aperture is still visible — b = S g / (v - g). This is the soft edge, and it is the whole of what geometry gives you
5. 5The shadow is magnified by v / (v - g) — Raise a tool to soften its edge and its shadow grows in the same proportion, so the tool must be cut smaller

A section, drawn to show the construction rather than to scale: a real enlarger's aperture is a few millimetres across and its lens-to-paper distance a few hundred, so the two triangles are far more slender than they are drawn here.

Run it for three formats, all at f/8, all printing to a full 8 × 10 in sheet. These are the course’s own arithmetic from the two Part XVI relations, not figures from a manufacturer.

Enlarger	S	v	b at g = 50 mm	at 100 mm	at 200 mm	at 300 mm
50 mm lens, 35 mm negative, m = 6.7	6.25 mm	385 mm	0.9 mm	2.2 mm	6.8 mm	22 mm
80 mm lens, 6 × 6 cm negative, m = 3.6	10.0 mm	368 mm	1.6 mm	3.7 mm	11.9 mm	44 mm
150 mm lens, 4 × 5 in negative, m = 2	18.75 mm	450 mm	2.3 mm	5.4 mm	15.0 mm	38 mm

Three things fall out of that table, and all three are useful at the easel.

A card near the paper leaves a hard edge, and the number says how hard. Ware puts the eye’s resolution at about 0.1 mm at its near point of 250 mm and takes 0.3 mm of blur as the onset of a visibly soft image. A card 50 mm above an 8 × 10 print leaves a transition one to two millimetres wide, ten to twenty times that limit: not blurred but fully resolved, and a resolved ramp with a third of a stop across it is “you can see the card”.

Raising the tool is the only geometric softener you have, and it costs size. Multiply g by four and b grows by more than four, because v − g shrinks as g grows — but the shadow is magnified by v ÷ (v − g) too. A dodger at 200 mm on the 50 mm enlarger above casts a shadow 2.1 times its own size, so a 45 mm oval on the print needs a 21 mm blade.

Opening the lens softens every edge at once, and Rodenstock say what it costs. b is inversely proportional to N, so f/5.6 gives edges about 40 per cent softer than f/8 — but Rodenstock recommend stopping their general-purpose enlarging lenses down two to three stops for optimal contrast and sharpness into the corners. Buying soft edges by opening up is buying them with definition: a legitimate trade that goes on the map, because a later print at f/11 will not have the same edges.

Stage 3 — motion, and what it actually contributes

If the geometry gives two millimetres and the picture needs twenty-five, the other twenty-three come from moving the tool. This is where the vocabulary goes vague — “keep it moving”, “feather it” — and where a little analysis pays for itself.

Motion adds its excursion to the transition. Sweep the tool through a peak-to-peak distance p measured at the paper and the boundary is smeared across p, so the transition is about p + b wide. The motion is magnified by the same v ÷ (v − g) as the shadow: a hand moving 10 mm at 200 mm on the 50 mm enlarger moves the shadow 21 mm, which with b = 6.8 mm gives a transition near 28 mm — reached with a ruler, not a feeling.

What the motion does to the tones inside the band is a matter of how long each point spent covered. A point in the middle is covered for part of the exposure and not the rest, and the covered fraction varies smoothly from nothing at one end of the sweep to everything at the other. That is the ramp, and three consequences follow, stated as the course’s own analysis of the geometry rather than as anybody’s published rule:

• One traverse already produces a ramp. Keeping the card “constantly moving” is not what produces a gradient; a single steady pass gives one.
• What several traverses buy is averaging. With one pass, position is perfectly correlated with time, so a wobble in hand speed or a drift in the lamp prints as a change in the gradient; with several, those errors spread across the band instead of being recorded in it. Two or three complete traverses during the shortest move you make is a working minimum — a judgement, not a measurement.
• A hand that slows at each end of its sweep is right; one that stops is not. Decelerating into a turn leaves the extreme positions covered slightly longer, which rounds the ends of the ramp and gives the transition no findable beginning. A pause holds one position for a measurable slice of the exposure and prints a step, which looks like a faint line inside an otherwise soft gradient and is the commonest reason a burn “nearly works”.

Wall’s dictionary reaches the practical half of this in 1912 twice over: for combination printing the mask “may be gently moved up and down near the sensitive surface”, and a vignetter in front of the lens is “gently moved backwards and forwards an inch or two during exposure”. An inch or two, gently, is an excursion and a speed.

✦The burn that is too short to move

A quarter-stop burn on a 12 second base adds 12 × (2^0.25 − 1) = 2.2 seconds, and two traverses in 2.2 seconds is a hurried, jerky sweep. The fix is not a faster hand: stop the lens down one stop and double the base, which turns the same quarter of a stop into 4.5 seconds of unhurried movement and incidentally hardens every edge by a factor of two, which you then compensate by raising the tool. Both changes go on the map.

Stage 4 — every move in stops, and the arithmetic of adding them

Part XVII owns the two expressions and this page uses them without re-deriving them.

Δt = t × (2^s − 1)

Extra time for a burn of s stops

Δt = t × (1 − 2^(−s))

Time withheld for a dodge of s stops

t is the base exposure and s the size of the move. The asymmetry is real: one stop of burn adds the whole base time again, one stop of dodge withholds only half of it.

The course’s convention, so that a map is unambiguous: every increment is a fraction of the base exposure, never of what that area happened to receive. Without that rule, a map carrying both a dodge and a burn on one area cannot be read, because “burn it half a stop” would mean two different times depending on the order. With the convention fixed, an area given the base exposure and then two burns of s₁ and s₂ has received

t_total = t × (2^s₁ + 2^s₂ − 1)

Two burns on the same area

🧮Why half a stop plus half a stop is not one stop

Two burns of half a stop each, on a base of 12.0 s. Each adds 12 × (2^0.5 − 1) = 4.97 s, so the area receives 12 + 4.97 + 4.97 = 21.94 s. In stops that is log₂(21.94 ÷ 12) = 0.87 stops, not 1.00.

The second burn is measured against the base, not against what the area already had. Three times gives log₂(3 × 1.414 − 2) = 1.16 stops rather than 1.50: the returns diminish, and a printer adding half-stops to a stubborn sky is climbing a curve that flattens.

Now the case that catches everybody. Dodge an area half a stop during the base and burn it half a stop afterwards: it receives 12 × 2^(−0.5) = 8.49 s of base plus 4.97 s of burn, which is 13.46 s — 0.165 stops darker than the base, not back where it started. That is the arithmetical reason the printing map keeps the two as separate rows and never nets them off.

Where the stops earn their keep is next month. Half a stop of burn is 5.0 s on a 12 second base and 9.9 s on the 24 second base one more enlargement asks for. The instruction did not change; the seconds did.

Stage 5 — the first dodge and the first burn, and what each one costs

Now make prints. Take one marked area, give it one move, process, dry, number and look. Dodges come first, because a dodge happens during the base exposure and constrains what follows.

9. Dodge. Start the base exposure, bring the blade in at the height stage 2 computed, keep it moving through its planned excursion, and withdraw it. The withheld time comes off the base, so a half-stop dodge on 12.0 s covers that area for 12 × (1 − 2^(−0.5)) = 3.5 s of the twelve.
10. Burn. After the base exposure ends, set the timer for the increment, shield everything but the target area, and give the extra. Two thirds of a stop on 12.0 s adds 12 × (2^0.667 − 1) = 7.0 s.
11. Number every print on the back in pencil before it goes in the developer — print number, base exposure, filter and the single change — then process and dry it. Reading a local move wet is the same error as reading a base exposure wet, and worse here, because dry-down acts most on exactly the light tones a dodge was protecting.

📷What a dodge costs, and why it is not free

A dodged area receives less exposure, so it sits lower on the paper’s characteristic curve, nearer the toe, where the slope is shallower. A shallower slope means less density difference for the same exposure difference, so the tones inside a dodged area come out less separated than before you touched them. That is the mechanism behind a dodged shadow going “flat” or “muddy”: you did not remove detail, you moved it onto a part of the curve that renders detail weakly. Push further and the area lands on the flat foot of the toe, where a range of negative densities maps to one paper tone — the grey hole, a patch of featureless light grey where the picture needed a black.

A dodge buys visibility in a shadow and pays in separation within it. Half a stop is usually invisible as a cost; a stop and a half rarely is. When the cost becomes unacceptable the answer is not a smaller dodge but a locally harder exposure, which is stage 7.

📷Why some burns darken and others darken convincingly

A burned highlight moves the other way — up out of the toe onto the straight line, where the slope is greatest. So where the negative holds separation, a burn does not merely darken the highlight, it increases the separation, and the sky acquires clouds it appeared not to have.

Where the negative holds none, nothing appears: burning a highlight that is blank on the film delivers an even grey that gets more emphatically even the more you give it. That is the difference between darkening an area and darkening it convincingly, and it is decided on the negative rather than at the easel — blocked highlights has the diagnosis. There is a ceiling at the other end too: burn far enough and the area climbs onto the shoulder, where the slope falls away and everything compresses towards maximum black.

Skies and windows both take the straight-edged card, and what separates them is where the transition may lie. A sky has no boundary of its own, so the transition can be as wide as you like; a window is bounded by a frame the viewer can see, so the burn lands inside that line and the softness has to fit within it. Feathering across a window frame reads as a mistake rather than a gradient.

Faces and hands are the hardest case, because the transition falls across a shape the viewer already knows. Two rules follow from stage 2 rather than from taste: work high, so that b is large before you have moved at all, and use a tool whose shadow is smaller than the area, moved generously, rather than one the size of the area held still.

Stage 6 — edges, and the falloff you already had

An edge burn darkens the margins so that the eye, which follows brightness, turns back into the picture instead of running off it — a reason that is not modern. Abney’s 1905 manual states it as a principle: where a secondary object “attracts the eye by the brilliancy of its high lights”, and “the object of all artistic photography is to cause the eye primarily to dwell on the most important point”, the bright area “should be sunned down by shading all the print except that particular part” through a brown-paper mask cut to shape. Wall defines vignetting in 1912 as “shading off the margins of a picture, so as to cause the figure or subject to gradually fade away”, adding that “the farther the vignetting shape is placed from the negative the larger the vignette and the softer the outline” — stage 2’s relation, a century early.

12. Read your enlarger’s certificate before you burn an edge. The corners are already darker than the centre from the lens’s own falloff, and Part XVI puts a number on the geometric floor: at 4× with a 50 mm lens the cos⁴ reference alone puts the corner about one third of a stop down, roughly 0.20 in reflection density on a mid-grey, and Rodenstock publish their measured falloff against that reference curve. An enlarger hands you a third of a stop of edge burn for nothing.
13. Give the edge burn as a measured sweep, not a wave of the hand. Hold a card at the computed height, sweep it in from each side in turn, and give each side the increment on the map. Corners take two sweeps and so roughly twice the added time, which by stage 4’s arithmetic is not twice the stops: a quarter of a stop on each of two sides leaves the corner log₂(2 × 1.189 − 1) = 0.46 stops darker, not 0.5.
14. Judge it dry, at the distance the print will be seen from. Dry-down deepens an edge burn like everything else: a burn that was a whisper in the tray is a band on the dry sheet.

Decision or mannerism: the course’s position, stated as a position. An edge burn is a decision when you can write what it is for in the map’s intention field, and a mannerism when the honest sentence is “I always do this”. Two tests are more useful than the sentence. Can you find its boundary on the dry print at viewing distance? A burn whose edge you can point at has become a frame drawn on the picture. And is it symmetrical because the picture asked, or because the sheet is a rectangle? No measurement stands behind either test, and the course does not pretend one does.

Stage 7 — local contrast, given through a second filter

The one thing filtration can do and geometry cannot is change the slope inside a bounded area — that is, local contrast. ILFORD name it in the same sentence as dodging and burning, among the simple techniques that can be used to great effect: “using different contrasts for different areas of the print”.

The mechanism is the previous lesson’s and is used rather than re-argued. A variable-contrast paper carries emulsion components sharing a blue speed and differing in green speed, and a magenta filter absorbs green while a yellow one absorbs blue. A burn through magenta therefore delivers a blue-weighted increment, which the components answer to together over a short exposure range, so inside the burned area the tones separate more steeply — while the rest of the print is untouched, because it received none of that light. A burn through yellow does the reverse: it darkens the area while reducing the separation in it, which is what a sky wants when it is already contrasty enough and merely too bright.

15. Give the base exposure at the print’s own filtration, then change the filter, shield everything but the target area, and give the increment.
16. Expect to need more time than the same increment at the print’s own grade. ILFORD state that grades 00 to 3.5 are speed matched and need little or no adjustment between them, while grades 4 and 5 “will generally require more exposure, in practice between 0.5 and 1 stop depending on the product”; their contrast-control sheet says filters 4 to 5 need double the time. Neither is a universal constant — Foma publish their own lengthening factors for the same ILFORD filters on Foma papers, and they differ again.
17. Record the move so that it can be repeated. A two-filter local move needs four things on the map, not three: the area, the filter, the increment as a fraction of the base exposure, and the exposure factor you used for that filter on that paper. The fourth is the one that gets left off, and without it the row describes an evening.

!Where a locally hard burn beats a harder print, and where it does not

A global grade change moves the whole scale. If the problem is that two mid-tones in one region are a tenth of a stop apart, going a grade harder separates them and simultaneously drives the shadow past maximum black and the highlight off the top — a poor trade for one region. A locally harder burn separates them and leaves the ends of the scale where they were, which is the strongest argument for owning a filter set rather than a single grade.

What it cannot do is invent separation. Where two tones have the same density on the negative, no filter and no exposure produces a difference between them; filtration redistributes what the negative holds, and no technique on this page moves that limit.

Stage 8 — one change per print, and the versions you keep

18. Change one thing per sheet, which is the rule Part IX applies to developers: a print that changes three things teaches nothing, because a visible difference cannot be attributed to any of them. A session that changes one thing per print converges; one that reacts to whatever looks worst oscillates.
19. Number every print, keep them all and dry them all, the number going on in pencil before the print is wet, with the change it embodies. A print with no number is a picture; a numbered print is data.
20. Compare dry against dry, side by side, under the same viewing light, with the ring-around beside them. A wet print and a dry one are different materials.
21. Accept that the fourth print is not reliably better than the second. A run of three sheets that each looked like an improvement can end somewhere worse than it started, because each was judged against the one before rather than against the intention. Lay the sequence out, read the intention again, and choose. Sometimes the answer is number 2.

=The two failures that end a local-control session badly

Chasing. A boundary shows, so the next print gets a bigger move to bury it, which shows more, so the next gets a different tool. That is not a printing problem; it is stage 2 arithmetic never done. Stop, measure the tool height, compute b, and cut a tool to size.

Compounding. The sky needs a third of a stop, so does the corner, so does the foreground, and by print six the effective base is half a stop longer than the one on the map — the print keeps getting darker while every individual decision was to lighten something. Total the increments as stage 4 does, and if the whole print is a third of a stop dark the honest fix is a shorter base exposure, not seven small dodges.

Stage 9 — closing the map, and the repeat test

The course's own notation for a printing map's local moves

1. ASky, +2/3 stop, filter 5, card at 180 mm, after the base — A hard burn: darkens and separates at once
2. BFace, -1/3 stop, print filter, 20 mm blade at 200 mm, during the base — A dodge is always during the base, which is why it has an order
3. CLower left corner, +1/3 stop, print filter, card at 120 mm, after — Check the enlarger certificate first: the corner may already be a third of a stop down
4. DRight edge, +1/4 stop, print filter, card at 150 mm, after — Given as one sweep per side, so the corner where D meets C gets both

No manufacturer document in this course's corpus gives a notation for recording local moves. This one is the course's own, and it is defined here so that the maps in this part can be read by somebody who did not write them.

22. Fill the map completely before you leave: the base exposure with everything it depends on (aperture, magnification, filter, lamp warm-up state, developer and its age, time, temperature, agitation); every local move as a row of the notation above; the dry-down correction; the paper, its surface and its box and batch; and the version number of the print you chose.
23. Then do the repeat test. Put the map away for three weeks, come back, make the print from the map alone without looking at the original, and compare them dry, side by side.

⁇What the repeat test can honestly promise, and what it cannot

The test is a test of the map, not of the paper, and the two manufacturer statements in this corpus disagree about how much the paper contributes.

ILFORD’s ILFOBROM GALERIE FB sheet states that the paper’s deep blacks, brilliant whites and neutral image colour “can be relied upon from print-to-print and batch-to-batch”. Foma’s FOMATONE MG Classic sheet runs the other way: selected emulsion batches suit the lith process, and because of the interactions involved “it is necessary to test each emulsion lot separately (especially the modification of the exposure and developing time)”. One is a graded fibre paper and a general claim; the other a warm-tone variable-contrast paper and a warning about one demanding process. Neither is a tolerance, and no maker in this corpus publishes a batch-to-batch variation in stops for enlarging paper, so the course states none.

What follows for the test. Run it on paper from the same box wherever you can, and the local moves should reproduce to about the resolution your ladder had — a third of a stop, the unit the map’s increments were chosen in. Where the box has changed, re-establish the rebate anchor first and carry the map’s stops rather than its seconds: the moves are ratios and survive a speed change, the base exposure is an absolute and does not. If the two prints differ in overall density with the local relationships intact, that is the paper and the map was right; if the local relationships differ, that is the map.

Expected observations

Stage 2. A card 50 mm above the paper leaves an edge you can find with a fingertip on the dry print; at 200 mm it leaves one you have to look for. The change is larger than the factor of four suggests, because the shadow grows with it.

Stage 3. A single unhurried traverse gives a usable gradient. A hand that pauses at a turn leaves a faint line there, and a burn under about three seconds usually shows the tool.

Stage 5. A half-stop dodge is usually invisible as a move and visible as a slight loss of snap inside the area. A two-thirds-stop burn on a sky with separation on the negative brings out structure; on a blank sky it produces flat grey and gets flatter the more you give it.

Stage 6. The edge burn looks smaller in the tray and larger on the dry sheet, and corners come out darker than asked for by roughly the falloff on your certificate.

Stage 8. The sequence will not improve monotonically.

What is happening chemically

Nothing here is a new reaction. It is the chain Parts IV and XVIII established — photon → electron → latent image centre → development to metallic silver — applied to an exposure delivered in pieces instead of all at once, and three of its consequences carry the session.

Exposures add, and the corpus supports treating them as additive here. A burn is a second instalment of light on a sheet that already holds a latent image, and ILFORD state that no significant change in picture quality is seen when MULTIGRADE RC papers are left 24 hours between exposure and processing — latent-image fading measured over a period four orders of magnitude longer than the pause while you fetch a card. The classical intermittency caveat, and the reasoning that disposes of it, belong to the split-grade lesson.

The paper’s curve converts a local exposure change into a local tonal change, and its slope is not the same everywhere. That is the mechanism behind both callouts in stage 5: the same third of a stop moves a toe tone hardly at all, a straight-line tone a great deal, and a shoulder tone hardly at all again. A printer who thinks in stops and is surprised by the result is meeting the curve, and the curve is Part XIII’s.

Development is to completion, which is what makes any of this repeatable. Once every crystal carrying a latent image centre has been reduced, more time adds no image density, so the print is a map of exposure and nothing else and a local move means the same thing on every sheet. Pull a print early because it “looked right” and printing by inspection has made density a function of exposure and time, turning every number on the map into a number about one sheet. That is why FB development extends to six minutes with no noticeable change in contrast or fog: past completion, time has stopped being a variable.

Data to record

The chain and the geometry, once, in the previous lab’s wording so the two records read as one document: paper, box and batch; developer, dilution, temperature and sheets through the tray; development time to the second and agitation in words; drying method and the delay before reading; enlarger, lens, aperture, magnification, filtration and warm-up state.

Every print, in a numbered row: number, the single change from the one before, the exposure arithmetic in full, and what you saw on the dry sheet — a description, not a verdict. “Sky better, corner now heavy” is data; “worse” is not.

Every tool, with its geometry: what it is, the height, the excursion swept and the computed b. A dodger labelled “20 mm blade, 200 mm, sweeps 10 mm, b = 6.8 mm at f/8 and m = 6.7” is equipment; an unlabelled oval on a wire is a piece of wire.

The moves that failed, with the reason: a record of the successful print alone sends its next reader down the same wrong road.

Analysis

Total the increments and check them against the base. Add every burn as stage 4 does and ask what the average addition over the sheet is. More than about a third of a stop and the base exposure is probably wrong: re-anchor rather than adding a twelfth move.

Test the geometry against the print. Measure a deliberate transition on a dry print and compare it with p + b computed from the height and excursion you recorded. Consistently wider means your hand sweeps further than you think; narrower, check the aperture.

Say which decisions were judgements. Every number here is measured, computed or chosen: the base exposure measured, b computed, the size of every move chosen. Marking the third is what lets a later reader know where to look when the print does not work.

Troubleshooting

What you see	Where to look
A findable line at the boundary of a burn or dodge	The tool was too low, or held still. Compute b, raise it, sweep it
A faint line inside an otherwise soft transition	A pause at a turning point. Sweep without stopping, and stop the lens down to lengthen a move under about three seconds
The dodged shadow is open but dead	The cost stage 5 names: the area is on the toe. Use a locally harder exposure, not a bigger dodge
A burned sky is grey and featureless however much you give it	Nothing to separate: blocked highlights or a flat negative
Corners much heavier than the increment you gave	Two sweeps overlapped, plus the enlarger’s own falloff: read the commissioning certificate
The whole print drifts darker across the session	Compounding increments, or a cold head: session exposure drift
A pale patch exactly where the dodger was	Reflection off a shiny blade or a bare wire. Blacken it
Prints from the second hour lighter than the first	The developer is working: check the sheet count on your running total
Whites not white anywhere, including the margin	Safelight fog or paper storage fog; a packet open for three hours is the usual cause
A move right on the strip and wrong on the print	The strip was judged wet, or the dry-down correction was applied twice
Parallel marks reading as density	Squeegee lines. Squeegee everything or nothing, identically

Clean-up

Dishes and tongs washed in the order developer, stop, fixer, rinsed between and dried face down, each pair with its own dish. Easel wiped and its blades checked. Filters wiped and returned to their envelopes, which ILFORD ask for specifically because marks from dust, rough handling or fingers reduce print contrast and degrade the image — and tonight they were handled wet. Lens capped. Run lab closing and darkroom closing.

Storage

The tools are kept and labelled, in an envelope with the map, marked with the height they were used at and the enlarger they were computed for: a dodger is reusable only if its geometry travels with it. The whole print sequence is kept too, numbered, flat and out of light with the map — the evidence for every claim on it, and what makes the repeat test meaningful.

The developer goes back in its bottle only if it never went into a tray. Neither ILFORD nor Kodak publishes a route by which a tray of paper developer returns to stock, and a bath topped back into a bottle is a bottle of unknown bromide. The stop and the fixer are a different case and ILFORD say so: both can be used for more than one printing session. Bottle them labelled and dated, with the sheet count on the label.

Disposal considerations

Three streams, apart from the moment they leave the trays. Alkaline developer carries negligible silver on Kodak’s own figures for photoprocessing solutions, so what governs it is pH and aquatic classification. Acid stop goes in its own container and not the developer’s, because combining an acid with a sulfite-bearing alkali is how a tray becomes a source of sulfur dioxide. Spent fixer and the first wash hold dissolved silver thiosulfate complexes and belong to Part XII’s silver stream under the silver-bearing waste procedure.

Keep each stream separate, labelled and closed, and take it to a facility that accepts it. Local regulation governs and differs by jurisdiction; check your local regulations and read the disposal caveat before acting on anything above.

Questions

1. An 80 mm lens at f/8, a 6 × 6 cm negative at m = 3.6, and a transition about 30 mm wide wanted across a horizon. Give a tool height and an excursion that deliver it, and say how big the card’s shadow will be compared with the card.
2. A sky is burned two thirds of a stop and, on the next print, another third on top. What is its total exposure in stops above the base, and why is it not one stop?
3. An area is dodged half a stop and later burned half a stop. Where does it end up relative to the base, and what does that imply for the map?
4. A print’s corners look a full stop heavier than the quarter-stop edge burn you gave. Name three contributions and say how you would separate them.
5. Why does a burn through a magenta filter separate tones inside the burned area, while the same increment at the print’s own grade mostly just darkens it?
6. A print repeated from its map three weeks later, on paper from a different box, comes out evenly a third of a stop dark with every local relationship intact. What went wrong, what did not, and what do you change?

Further experiments

Measure the penumbra instead of computing it. Tape a straight-edged card at a measured height, give a one-stop burn without moving it, and measure the transition on the dry print with a loupe and a rule, at four heights and two apertures. Plot the measured widths against the computed S g ÷ (v − g): a consistent offset is telling you something about flare.

Find your own threshold for a visible boundary. No source in this corpus gives the width at which a tonal transition stops being findable. Make one-stop steps with transitions of 1, 2, 5, 10, 20 and 40 mm, dry them, find the width at which you can no longer locate the boundary, and publish the viewing distance and density step with the answer.

Test the intermittency assumption for a burn. Give one sheet its base plus a two-thirds-stop burn over the whole frame as two exposures, and another the same total in one — same bath, same evening, same drying. The course treats additivity as sound on published reasoning rather than on a measurement of modern paper, and a careful measurement published with its method would be a real contribution.

Recap

• Local control is mostly geometry and arithmetic, and only then taste. The soft edge a tool leaves is b = S g ÷ (v − g), Part XVI’s penumbra relation applied to the enlarger’s own aperture; for a low tool it is the height divided by the effective f-number N(1 + m).
• A card near the paper leaves a hard edge: one to two millimetres on an 8 × 10 print, against an eye that resolves about 0.1 mm at its near point. Geometry will not hide a boundary, so motion supplies the rest. One steady traverse already gives a gradient; several average out an unsteady hand; a decelerating turn rounds the ends of the ramp; a pause prints a step, and that faint line inside a soft transition is the session’s most diagnostic mark.
• Every increment is a fraction of the base exposure, never of what the area received. So half a stop plus half a stop is 0.87 stops, and a half-stop dodge followed by a half-stop burn leaves the area 0.165 stops darker than the base — which is why dodges and burns are separate rows, never netted off.
• A dodge buys shadow visibility and pays in separation, because the area moves onto the shallow toe; overdone, it is a grey hole. A burn moves a highlight up onto the straight line, so it can darken and separate — but only where the negative holds separation to begin with.
• Edge burning has a documented rationale and an undocumented dose. Abney gives the reason in 1905 and Wall the geometry in 1912; neither gives an amount, and this course will not invent one. What it adds is that your enlarger already contributed about a third of a stop at the corner.
• A locally hard or soft burn is the one move filtration can make and geometry cannot, and ILFORD list different contrasts for different areas among the techniques a printer should know. Record the filter and the exposure factor, or the row is unrepeatable.
• One change per print, every print numbered, kept and judged dry side by side. The fourth print is not reliably better than the second.
• The map is the deliverable. No manufacturer in this corpus publishes a notation for it, so the course defines its own and says so: area, size in stops, filter, tool and height, order. Where the paper box has changed, carry its stops rather than its seconds — no maker publishes a batch-to-batch tolerance and this course will not supply one.

Check your understanding

Question 1. You are printing a 35 mm negative at m = 6.7 with a 50 mm lens at f/8, so the lens sits 385 mm above the paper and its aperture is 6.25 mm across. You hold a card 100 mm above the paper. Roughly how wide is the soft edge it leaves, and what happens to the card’s shadow?

• About 0.3 mm, and the shadow is the same size as the card
• About 2.2 mm, and the shadow is about 1.35 times the size of the card
• About 6.25 mm, because the penumbra equals the aperture diameter
• It cannot be calculated without knowing the paper’s contrast grade

Show the answer and why

Answer: About 2.2 mm, and the shadow is about 1.35 times the size of the card

b = S g / (v − g) = 6.25 × 100 / (385 − 100) = 2.19 mm, and the shadow is magnified by v / (v − g) = 385 / 285 = 1.35. Both come from the same pair of similar triangles, which is why they move together: raising a tool to soften its edge also enlarges what it covers, so a tool cut to the size of the area it is meant to shield will over-shield it. The 2.2 mm figure is the useful one at the easel — against an eye that resolves about 0.1 mm at its near point, a 2 mm transition is fully resolved, so the boundary is findable and the rest of the softening has to come from moving the card.

Question 2. A printer burns a sky half a stop, looks at the dry print, and burns the same sky another half a stop on the next sheet. How much darker than the base is that sky, and why?

• One stop, because half a stop plus half a stop is one stop
• About 0.87 stops, because each increment is measured against the base exposure rather than against what the sky had already received
• Two stops, because the burns multiply
• It depends on the paper grade and cannot be calculated

Show the answer and why

Answer: About 0.87 stops, because each increment is measured against the base exposure rather than against what the sky had already received

Each half-stop burn adds t(2^0.5 − 1) = 0.414 t, so the sky receives t(1 + 0.414 + 0.414) = 1.828 t, which is log2(1.828) = 0.87 stops. The convention that every increment is a fraction of the base — not of what the area actually got — is what makes a map readable, and this is its arithmetical consequence: successive burns show diminishing returns, and a printer adding half-stops to a stubborn sky is climbing a curve that flattens. The same arithmetic shows that a half-stop dodge followed by a half-stop burn does not cancel but leaves the area 0.165 stops darker than the base, which is why the two are recorded as separate rows with an order.

Question 3. A dodged shadow opens up as intended, but the detail inside it looks weak and flat. What has happened?

• The developer is exhausted and needs replacing
• The dodge withheld exposure, so the area now sits nearer the toe of the paper’s curve, where the slope is shallower and the same negative density differences render as smaller density differences on the print
• The dodger was held too high, so the edge is soft
• The negative has no detail in that shadow and the dodge revealed it

Show the answer and why

Answer: The dodge withheld exposure, so the area now sits nearer the toe of the paper’s curve, where the slope is shallower and the same negative density differences render as smaller density differences on the print

This is the cost of dodging and it is structural rather than a fault: less exposure means a lower point on the characteristic curve, and the toe is where the curve is shallowest, so tonal separation inside the dodged area falls even though its average lightness rose. Overdone, the area lands on the flat foot of the toe and a range of negative densities collapses into one light grey — the grey hole where the picture wanted a black. The last option is worth ruling out too, and the test is the negative rather than the print; but if the shadow does hold detail, the answer is not a smaller dodge, it is a locally harder exposure, which separates the tones instead of merely raising them.

Question 4. Why does the course say that no manufacturer notation for a printing map exists, rather than simply giving one?

• Because manufacturers regard the notation as a trade secret
• Because the corpus was searched and none was found: ILFORD name dodging and burning in a single clause of a beginner sheet, Kodak’s printing guides do not mention them at all, and the historical manuals describe the operations without any written notation — so the course defines its own and labels it as its own
• Because notation is a matter of personal taste and cannot be standardised
• Because the course prefers to record everything in seconds

Show the answer and why

Answer: Because the corpus was searched and none was found: ILFORD name dodging and burning in a single clause of a beginner sheet, Kodak’s printing guides do not mention them at all, and the historical manuals describe the operations without any written notation — so the course defines its own and labels it as its own

Rule 7 asks that fact and interpretation be kept apart, and a convention presented as though a manufacturer published it would fail that test. What the corpus actually holds is the technique without the paperwork: ILFORD describe using hands or card to hold back or add light, and name different contrasts for different areas as a further technique; Abney in 1905 and Wall in 1912 describe shading, sunning down and vignetting in detail, including the observation that the farther the mask sits from the negative the softer the outline. None of them writes a move down in a reproducible form. So the notation on this page — area, size in stops, filter, tool and height, order — is the course’s own, and saying so is what allows a reader to disagree with it.

Question 5. Three weeks later you make the print again from its map alone, on paper from a new box. Every local relationship is intact but the whole sheet is about a third of a stop dark. What is the right conclusion?

• The map is wrong and every local move needs re-measuring
• The map is sound; the absolute base exposure did not travel across a paper change, so re-anchor the base and keep the moves, which are ratios
• The paper is faulty and should be returned
• The developer must have been mixed at the wrong dilution

Show the answer and why

Answer: The map is sound; the absolute base exposure did not travel across a paper change, so re-anchor the base and keep the moves, which are ratios

The local moves are expressed as fractions of the base exposure, so they are ratios and survive a change in paper speed; the base exposure is an absolute number in seconds and does not. An even overall shift with the internal relationships preserved is therefore the signature of a speed change rather than of a bad map. No manufacturer in this corpus publishes a batch-to-batch tolerance in stops — ILFORD claim print-to-print and batch-to-batch reliability for one graded fibre paper, Foma warn that each emulsion lot needs testing separately for lith — so the course states no tolerance and gives a procedure instead: re-establish the anchor on the new box, keep the stops, and note the new batch on the map.

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