Part XVI Overview: Build the Darkroom

Every part before this one worked around not having a darkroom. Part II commissioned a temporary laboratory, Part IV ran a session in it, and Part VI’s camera had to be light-tight precisely because the room was not. Eight later parts stop working around it: printing, toning, the alternative processes and the capstone all assume a room that goes dark on demand, a lamp you can see by that does not touch the paper, a way of putting light through a negative and a way of enlarging it.

This part builds those, and one rule governs it.

The rule of the part

A lamp is not safe because it is red, and a light box is not even because it looks even. Every performance claim on these pages is a measurement with a date on it, made by you, on your room, with your material.

Kodak’s own guide states it in the negative: no safelight protects a material for an indefinite period, filters fade as they are used, and poor safelight conditions degrade highlights and lower print contrast before visible fog appears anywhere a reader would think to look. ILFORD define a safelight as the illumination that causes no significant visible change during use, and add that the word safe is relative. Neither can be satisfied by choosing a colour; both are satisfied by a number, and a number needs a test.

The four instruments, and what each must deliver

Instrument	Must deliver	Proved by
The room	Darkness sufficient for the material handled, and air	A leak test on paper, repeated on film
The safelight	A measured safe working time at a stated distance and setting	The before-and-after fog test
The contact printer	Even light over the printing area, and true contact	A uniformity map in density units
The UVA unit	A known dose, an even field and an interlock	Dose calibration against a step wedge
The enlarger	Three parallel planes and even illumination	Alignment measurement and a falloff map

Five rows for four instruments: the room is not an instrument, and everything else depends on it.

The order, and why it is that order

Room, then the light you work by, then contact printing, then the UV unit, then the enlarger. Not a preference: it is the order in which each build stops being untestable. You cannot test a safelight in a room that leaks, because you cannot tell which light fogged the sheet, and you cannot commission an enlarger without a safelight to work under. Contact printing comes before enlarging because it needs no enlarger — which is also the printing parts’ assignment path, from photogram to enlarged print.

The electrical rule, carried and not renegotiated

Everything you build here runs at 12 to 24 V or from USB, from a certified, enclosed supply, as Part XIV established. HSE’s reason is the course’s: limit the supply voltage to the lowest that will do the job, because 230 V AC can kill and the risk is greatest in wet surroundings — which is what a darkroom is.

No page in this part wires, modifies, re-terminates or opens anything at mains potential. Where a build meets a mains appliance — the donor enlarger’s lamphouse — the mains parts come out complete and are discarded, not rewired. Where a mains appliance must be switched, the plug-in route is specified and the fixed-wiring route is named as work for a competent person. Switched mains output was Part XVII’s subject until its survey of 5 September 2026 found no certified appliance switch to do it with; the timer that part builds therefore has one low-voltage output, and this part’s plug-in route is the only one there is.

Safety framing

Level A for the room, the safelight, the contact printer, the fog test and the enlarger commissioning; Level B for the UVA unit and the enlarger head conversion. The hazards that earn those letters are glass, working at height, ultraviolet radiation to eye and skin, and heat from a high-output emitter. The chemistry is the ordinary print sequence, Level A throughout.

What can be bought instead of built

Almost all of it: a commercial safelight, a used enlarger, a bought UV unit, a bought contact frame, sunlight instead of an array. Buying changes nothing about the tests. A twenty-year-old enlarger with an unknown history is not a certificate, and a bought safelight is a lamp whose safe working time in your room is still unmeasured. Each page carries its bought route beside its built one.

What you need first

Part IV’s spectral sensitivity, because the room is tested against a material rather than in the abstract. Part XIII for the curve the fog lands on. Part XIV’s electronics primer, assumed in full and never re-taught. Part XV’s densitometer for the quantitative half of every test here.

Cost, and what the planner cannot tell you

The builds sit in the planner’s stage 3, contact printing, and stage 4, the enlarger and timer. Stage 4 is the stage the planner records as unsettled, waiting on this part, and it carries one traceable item, an optional enlarger at £1,549. The planner prices no blackout fabric, no foam board, no door seal, no deep-red emitter and no enclosure hardware. Every page below names its own unpriced lines and reads its subtotal as a floor.

Alternative route

This is the part most likely to be read by somebody who cannot do all of it — a rented flat, a shared bathroom, no plumbing, no space, no permission to fix anything to a wall. Every page states its minimum viable version, not only its good one, and those minima are real routes rather than consolation: a reversible blackout that leaves no mark, a changing bag or tent instead of a dark room, night working, a daylight tank, a bought lamp tested rather than a built one, sunlight instead of a UV array, a contact frame instead of an enlarger. What none of them substitutes is the test. A reader with a temporary blackout still measures their safe working time, and the number is as real as anyone’s.

!One honest limit before you start

A room that passes the leak test on photographic paper may still fog panchromatic film, which is slow and red-blind against fast and sensitive to everything. Kodak’s list of materials to be handled in total darkness begins with panchromatic film. Nothing here makes a room safe for material that has no safelight; it makes a room whose limits you know.

The pages of this part

Part16 of 28Level3 — AdvancedPages11Estimated time25.5 hoursHighest safety levelLevel B

✱7 of 11 pages in this part need a darkroom, a UV source or mains-powered equipment, marked below. Each says what can be improvised and, where one exists, gives an alternative route.

0 / 11 lessons in this part completed

• BuildBuild: Making a Room Dark and Proving ItA✱ Darkroom150 min
• LessonSafelight: Spectra, Distance, Duration and the Fog Limit60 min
• BuildBuild: An LED SafelightA150 min
• ExperimentExperiment: The Safelight Fog TestA✱ Darkroom120 min
• BuildBuild: The Contact Printing Frame and Its Light SourceA✱ Darkroom180 min
• LessonUltraviolet for the Alternative Processes: Sources, Dose, Uniformity and HazardB60 min
• BuildBuild: The UVA Exposure UnitB✱ UV240 min
• LessonEnlarger Optics: Condenser, Diffusion, Lens, Alignment and Falloff75 min
• BuildBuild: An LED Enlarger HeadB✱ Darkroom240 min
• ExperimentExperiment: Commissioning the EnlargerA✱ Darkroom180 min
• Break/fixBreak/Fix: The Room That Fogs and the Light That Is Not EvenA✱ Darkroom75 min