Standard operating procedures

A lesson explains. A procedure is followed — by somebody who has already read the lesson, who is now doing the thing, possibly in a hurry, possibly with wet hands, and who needs the next step rather than the argument for it. Those are different documents and this course keeps them apart.

Everything here is written for the second case. The steps are imperative and numbered. Nothing is explained; where a step depends on a mechanism, the page that teaches the mechanism is linked and the procedure moves on. Every one of them is short enough to print.

What an entry contains

Seven sections, in the same order every time, so that a reader looking for one of them knows where to look.

Section	What it holds
Purpose	What following this leaves you with. One or two sentences.
When to use it	The moment it is run — and, where it matters, when it does not apply.
Before you start	What you must already be able to do, and what has to be on the bench.
Procedure	Numbered imperative steps, running consecutively from 1.
How you know it worked	The conditions that are true at the end. A procedure with no completion test is a wish.
If a step fails	What to do when a step does not work, keyed to the step number.
What to record	The notebook line, the label, or the log entry the procedure produces.

!A procedure is not a licence

Every entry carries a safety level from the classification rubric, and the level is an assessment of that procedure, not of the substances in it. Following the steps does not make an operation acceptable in a room that does not meet the level’s controls. If you do not have those controls, the procedure is not classified for you, whatever its letter — and no procedure here is Level D, because Level D is historical study and gives no steps at all.

Where the steps come from

Every entry names, in its front matter and again in its Before you start section, the written course pages whose practice it records. That is not decoration: a build-time check fails if one of those pages does not exist, so a procedure cannot outlive the lesson it came from, and a part that is rewritten cannot leave a stale procedure behind it.

The rule the library is built on is the same one the safety library uses. A page cites rather than restates. Where a lab needs a reader to open the laboratory, it links opening the laboratory; it does not write its own version of the list, because two versions of one list is one version too many and nobody can tell which is current.

The review clock

Each entry carries two dates: when it was last read against the pages it records, and when it must be read against them again. The second is what makes the first mean anything. An overdue entry is reported by the build, so the library says out loud when it has stopped being maintained rather than going quietly stale — which is what happens to every procedure folder that has no clock on it.

Reading an entry again means checking each step against the page it came from, not skimming it for typographical errors. Where the lesson has changed, the procedure changes or it is retired.

What is not here yet

The library is deliberately short. A procedure is written when the part that owns the practice has been written, and not before: an SOP assembled from a lesson that does not exist yet would be this course inventing practice and then teaching it back to itself. The toning procedures, the printing line’s set-up and shut-down, the session log, the whole-room fog audit and everything the alternative processes need all belong here, and each is waiting on the part that owns it.

The procedures

Bench operations

• Adjusting pH with a concentrated alkaliBRun Whenever a bath's pH is moved, or an alkaline concentrate is made upReview due 2027-09-08Alkali into water and never the reverse, dosed from a dilute stock rather than a jar of pellets, read on a meter bracketed by two buffers, and written down as a change to a named bath rather than as an experiment on pH.
• Dedicating tools to one processARun Whenever two alternative processes share a room, a bench or a cupboardReview due 2027-09-08One brush, one tray, one pair of tongs and one funnel per process, marked so that a tired hand in dim light cannot pick up the wrong one, with the rod as the single shared implement because it is the only one that can be got genuinely clean.
• Glass handling, cutting and breakage responseARun Any time glass is carried, dressed, cut or broken in the darkroomReview due 2027-09-05Carrying, dressing and cutting glass so that it does not cut you, and the order of work after a sheet breaks — the person first, the liquid second, the pieces third, and a labelled sharps box rather than a bin bag.
• Hand-coating a sheet with a rod and with a brushBRun Whenever a sensitiser is put onto paper by handReview due 2027-09-08Tape the sheet level, mark the negative's corners, pour a measured volume, draw it out in a counted number of passes, blot the bead, rinse the rod at once, and dry in the dark without a hairdryer.
• Handling and storing a deliberately faulty reference specimenARun Whenever a fault is reproduced on purpose and the result is keptReview due 2027-09-08A specimen made on purpose is calibrated evidence and an unstable object at the same time — made with its own control, labelled with the conditions that produced it, sleeved on its own, and kept where it cannot reach finished work.
• Keeping the printing session logARun Every printing evening, opened before the first sheet and closed before you leaveReview due 2027-09-08One line per batch recording what the print was made in rather than what was done to it, so that a repeat print a year later has a short list of candidate causes instead of an unbounded one.
• Labelling a containerARun Before any container is filled, including a waste containerReview due 2027-09-04The fields every filled container carries — substance, strength, dates, hazard wording, initials and family, with four more for a waste container — written before the container is filled rather than afterwards.
• Loading paper and sheet film into a pinhole backARun Every time a sheet goes into a pinhole back, and every time one comes outReview due 2027-09-05Getting a sheet into a pinhole back and out again with no exposure it did not earn — the room proved dark, the emulsion side settled in the light beforehand, the sheet flat behind the stops, and the shutter shut before the dark slide moves.
• Measuring a clearing timeARun Before fixing anything you care about, and on the schedule the capacity log setsReview due 2027-09-05The drop-on-a-scrap test that decides how long to fix and when to retire the bath — the reference spot, three readings rather than one, the doubling rule, and the retirement criterion measured against the figure taken when the bath was fresh.
• Mixing a developer from raw chemicalsARun Whenever a developer is made up from weighed solids rather than from a packetReview due 2027-09-05A developer made from weighed solids — the version code assigned before anything is weighed, the weighing step worked at higher controls than the rest of the session, the order of dissolution the formula gives, and the bottle filled full and labelled with its measured pH.
• Mixing a fixerARun Whenever a fixing bath is made up, from solids or from a concentrateReview due 2027-09-05Making a fixing bath from solids or from a concentrate — the hydrate arithmetic checked before anything is weighed, the addition order that keeps acid away from undissolved thiosulfate, the alum last and cold, and the fresh clearing time that goes on the label.
• Mixing a solution to a final volumeARun Whenever a formula reads "water to" a stated volumeReview due 2027-09-05Dissolve in about three-quarters of the volume, transfer with the rinsings, top up to the mark at eye level, and calculate the strength from the mass and the volume you actually achieved rather than the ones you set out for.
• Mixing a working solution from a stockARun Whenever a page asks you to dilute a stock or a concentrateReview due 2027-09-04How to get from a bottle of stock to a stated volume of working solution at a stated strength — the calculation, the independent check, the make-up-to-volume habit, and the record of what you actually made rather than what you meant to make.
• Mounting a print and putting it in an enclosureARun When a dry, tested print is ready to be finished and storedReview due 2027-09-08Flatten a damp print rather than forcing a dry one, trim and spot it, attach it by a method that can be undone, buy the board against a standard rather than an adjective, and write the label nobody else can reconstruct.
• Opening and handling photographic paper in dim lightARun Every time a packet of photographic paper is opened and a sheet taken outReview due 2027-09-05Getting a sheet out of the packet and back again without giving it exposure you did not intend — the room checked first, the bag closed behind you, the sheet kept face down, and the clock running from the moment the packet opens.
• Recording a batch in the inventoryARun When a container arrives, when one is mixed, and when one is opened or finishedReview due 2027-09-05One line per container, carrying the identity fields that survive a change of supplier, the three dates that are three different clocks, the storage group, and the column that pays — which pages of the course use it.
• Recording a daylight exposureARun Every exposure made in daylight, from ruling the row up to filing it after processingReview due 2027-09-05The row that turns a sheet exposed in sunlight into a repeatable result — written before the card comes off, in fixed units and a fixed vocabulary for the sky, with every number either measured or naming where it came from.
• Refrigerated emulsion labelling and food separationARun Whenever emulsion goes into cold store, and once when the refrigerator is set upReview due 2027-09-05What goes on an emulsion before it enters cold store — batch code, stage, date in, a use-by date rather than a range, and the remelt count — and how the cold store is kept apart from anything anybody eats.
• Residual hypo and residual silver testsBRun After the final wash, on the control sheet carried through with the batchReview due 2027-09-05The two spot tests that separate a washing failure from a fixing failure — three minutes in one per cent silver nitrate read wet against the sheet's own untreated half, and a drop of diluted sulfide read against a reference spot on a print known to be well fixed.
• Running a two-bath fixing rotationARun Anything you intend to keep, and every fibre-base printReview due 2027-09-05Two baths of the same fixer, half the time in each, and the rotation that keeps the last bath a material meets close to fresh — with the promotion rule, the relabelling it forces, and the short-in-fresh rule that governs fibre prints.
• Stop bath preparationARun Whenever a stop bath is made up, from a solid acid, a dilute liquid or a concentrateReview due 2027-09-05Making up a working stop bath — the article on the jar read before the mass is weighed, the acid added to the water and never the reverse, the starting pH recorded, and the bath's capacity written on the label as a count of work rather than a date.
• Storage rotation and shelf separationARun When anything joins the shelf, and every time a container goes back on itReview due 2027-09-05Where a container goes when it arrives and where it goes back when you have finished with it — sorted by separation group rather than alphabetically, corrosives low, silver nitrate alone, oldest to the front, and a tray under everything that pours.
• Storing unfixed prints for later fixingARun When a print leaves the exposure unfixed and has to be kept before it can be fixedReview due 2027-09-05Sealing a print that has never been in a fixing bath so that it stops changing as far as it can — scanned first, labelled in pencil, inside a photo-safe enclosure inside a light-tight one, and logged every time it is opened.
• The acid exclusion rule at a hexacyanoferrate or thiocyanate benchBRun Whenever a ferricyanide or a thiocyanate is open, in a tray, or in a waste containerReview due 2027-09-08No acid enters the room, the bench or the waste bottle while a ferricyanide or a thiocyanate is out — with the one deliberate, dilute weak-acid exception the published processes call for, and the container discipline that is where the rule is actually broken.
• The stock check, and retiring a chemicalARun Once a quarter, and at the start of any part that introduces new chemistryReview due 2027-09-05The quarterly walk along the shelf with the inventory in hand — five questions of every container, one honest criterion for retiring one, and the note that turns a retirement into a measurement of your own storage.
• Versioning a formulaARun Before anything is weighed, whenever a batch is mixed or a variant is proposedReview due 2027-09-05Issue the code before anything is weighed — stem, initials, sequence — open the record it points at, keep the number out of a second bottle, and put the code rather than the recipe on everything the batch produces.
• Weighing a solidARun Whenever a formula gives a mass rather than a volumeReview due 2027-09-05Tare, add slowly, weigh by difference where the substance demands it, record the reading you got rather than the one you wanted, and rinse the weighing vessel into the batch so that what you weighed is what ends up in the solution.

Handling a substance

• Ammoniacal silver quench and prohibitionBRun Any moment an ammoniacal silver solution exists, by design or by accidentReview due 2027-09-05Destroying a diammine silver solution the moment it has done its job — the brine beaker charged before the ammonia bottle is opened, the immediate pour, the double rinse, the silver-bearing route — and the one finding at which this course stops and gives no procedure at all.
• Handling a selenium toner and its wasteBRun Any session in which a selenium toner concentrate is opened, worked or bottledReview due 2027-09-08A bought concentrate decanted once, worked in a dilute alkaline bath with no acid in the room, lifted with tongs rather than fingers, bottled rather than discarded, and routed to a collection point rather than a drain.
• Handling a sulphide toner and its wasteBRun Any session in which a sulphide toner bath exists in the roomReview due 2027-09-08The stock made on another day or bought ready made, the bath mixed last and discarded at the end of the session, the paper and every acid out of the room before the bottle is opened, and three waste containers that never share a funnel.
• Handling silver nitrateBRun Every time the silver nitrate bottle is openedReview due 2027-09-04Weighing, dissolving, using and putting away silver nitrate so that all of it ends where you intended — the tared glass vessel, the dedicated spatula, distilled water only, amber glass, and every rinse into the silver waste container.
• Recording a safety data sheetARun When a substance arrives, and again whenever the supplier or the packaging changesReview due 2027-09-05Get the sheet for the product actually in your hand, read the six sections that change what you do, record source, version, revision date and date read, file the dated file, and copy the hazard wording onto the label.
• Silver nitrate at the coating benchBRun Any session in which paper is sensitised with a silver nitrate solutionReview due 2027-09-08An extension of the Part II handling procedure for the bench where wet sheets are lifted dripping at face height — sealed goggles rather than spectacles, nothing metal, a drying line that is not over a walkway, and every drop collected.
• Weighing and handling developing agentsBRun Whenever a developing agent is weighed as a powderReview due 2027-09-08A Level B extension of the weighing procedure for the agents that are skin sensitisers and fine powders — the tray, the still air, one jar open at a time, the mask, and the wet clean-up, with the staining agents' alternative route named before the balance is switched on.

Incident response

• Checking and using the eyewashARun Once before every session, and the second anything reaches an eyeReview due 2027-09-05The tap is your eyewash, so it is proved before every session and reached with your eyes shut when it matters — water in, lid held open, kept running past the point where it feels better, and somebody else on the telephone.
• Handling a container found unlabelled or undatedARun You pick up a container and cannot say what is in it or how old it isReview due 2027-09-05The commonest real failure in a home darkroom, and the one procedure that never involves opening the bottle — put it down, write UNIDENTIFIED on it, decide whether you have lost the identity or only the date, and retire what you cannot state.
• Responding to a silver nitrate spillBRun Silver nitrate, solid or in solution, outside the vessel it belongs inReview due 2027-09-05Collected rather than mopped, never left to dry in a cloth, never into an open bin and never towards the drain, because this spill is an oxidiser sitting in whatever it landed on and a stain that will not show for hours.
• Responding to a spillBRun The moment something is on the bench or the floor that should not beReview due 2027-09-05Stop, decide whether this is yours to clean, protect yourself with new gloves, contain from the edge inwards or collect a solid dry, lift, wash, route what you collected, and write it down.
• Responding to a spilled solidARun A powder or crystal is on the bench, the floor or a garmentReview due 2027-09-05A powder on the bench is an inhalation hazard the moment anyone disturbs it, so it is lifted dry and slowly, never brushed and never wetted, and the residue is taken up damp only after the bulk has gone.
• Responding to an acid spillBRun Any acid on a surface, from a working stop bath to an opened concentrateReview due 2027-09-05An acid spill is a race between you and whatever salt of a weak acid it is running towards, so the first move after protecting yourself is to get the sulfite, the fixer and the waste containers out of its path.
• Responding to an alkali spillBRun Caustic solid, alkaline stock or ammonia solution outside its vesselReview due 2027-09-05A caustic spill is lifted dry if it is a solid, kept away from aluminium and never neutralised where it lies, because every shortcut that sounds clever here adds heat to a surface you are leaning over.

Instruments and calibration

• Blackout leak test after any change to the roomARun After any change to the room, its blackout, its material class or the seasonReview due 2027-09-05The re-test a room needs after anything about it changes — twenty minutes dark-adapted for the hunt, then a sheet of paper and its control left at the working position for twice the measured handling time, and a verdict written against a named material rather than against the word "dark".
• Calibrating a pH meterARun Before any session in which a pH reading will be recordedReview due 2027-09-04Two-point calibration at pH 7.00 and 4.01, a verification against a standard the calibration never saw, a closing drift check, and the electrode back in its storage solution before anything is written up.
• Calibrating the darkroom timerBRun At commissioning, after a firmware change, a repair, or a change of headReview due 2027-09-08Six arms that separate what the instrument commanded from what the lamp delivered and what the paper received, with the correction constant removed before the first reading and refitted before you leave the bench.
• Checking the balance and verifying the thermometerARun At commissioning, at your own stated interval, and after any knock or moveReview due 2027-09-04Drift, repeatability, trueness and off-centre loading for the balance; the ice point for the thermometer; an action written for each; and the deviation written on the instrument itself so it travels with it.
• Control strip processing and chartingARun Every processing run, once the aim and the limits have been establishedReview due 2027-09-05One pre-exposed strip in every tank, three numbers read from it, the deviation from aim plotted against the run date, the events written on the chart beside the points, and the rules for reading it without over-controlling a process that is only making noise.
• Densitometer daily five-minute checkARun At the start of every session, before the first reading anyone will useReview due 2027-09-05Warm up for the time your own drift curve set, take a dark and a zero, read the calibration step, and either work or recalibrate — plus the reflection anchors, the placement tolerance, and the band the reading is allowed to be quoted in.
• Enlarger alignment and uniformity checkARun After any move, knock, lens or carrier change, and at your own stated intervalReview due 2027-09-05The mirror null in two axes at both stages, a nine-point map read as density at two apertures, the two criteria that are a pass and the one number that is only ever recorded — run after any move, knock, lens or carrier change.
• Laser pointer use for pinhole measurement (Class 2 only)ARun Whenever a pointer is switched on to measure or inspect a pinhole by diffractionReview due 2027-09-05The diffraction measurement run as a procedure — the pointer read off its own label, the beam clamped below eye level and terminated on a matt wall, the first dark ring measured twice, and the diameter computed from a throw, a ring and a wavelength.
• Sensitometer exposure sessionARun Any session that exposes strips in the sensitometer for a measurementReview due 2027-09-05Warm the instrument for the time its own certificate states, load film and wedge against the fences with the wedge emulsion down, expose at a fixed cadence with the monitor logged, and report every log H with the two uncertainties the calibration measured.
• Testing a safelightARun After any change to the lamp, its bulb, its filter or its position, and yearlyReview due 2027-09-05The published before-and-after test that gives a safe time rather than an impression — a grey-tone exposure at each end of the strip, timed safelight steps at the brightest point in the room, and the verdict recorded against the geometry it applies to.
• Verifying volumetric glassware by weighing waterARun At commissioning, and for any new or unmarked vessel before it measures anythingReview due 2027-09-05Fill to the mark, pour, drain for five seconds, weigh what came out, and write the delivered volume on the vessel — the one check that tests the graduate you actually own rather than the tolerance class printed on a box.
• Whole-room fog auditARun Yearly, and whenever anything in the room changes what it emitsReview due 2027-09-05Every light in the room measured on the same paper, with the same grey-tone exposure and the same step series — one sheet per emitter, one sheet with everything on at once, and a fix-first order that comes out of the numbers rather than out of suspicion.

Opening and closing a session

• An emulsion preparation sessionBRun Making an emulsion, from the weighing to the coated sheet set to dryReview due 2027-09-05A plain-silver make from the weighing to a coated sheet — the salted gelatin brought to temperature, the silver added at the published rate, the hold, the set overnight, the noodle wash in ice water, the ripen, the finals and the coat, with every silver-bearing stream collected.
• Checking the ventilation before a sessionARun Before any session that opens a powder, an acid, a fixer or a warm bathReview due 2027-09-05Air in at the clean end and out where the vapour is made, proved with a torn strip of paper rather than assumed — with the arithmetic done once, the trays covered before a fan is bought, and a rule that ends the session if the direction cannot be made right.
• Clearing an iron-silver print and testing it for residual ironBRun Every Van Dyke and kallitype print, after development and before fixingReview due 2027-09-08Rinse neutral, clear in the order the pH argument sets, judge the end point on the masked border rather than the clock, and run the ferricyanide spot test at a station no acid can reach.
• Closing the laboratoryARun At the end of every session, before the room becomes a room againReview due 2027-09-05The pack-down run at the end of every session — waste routed and sealed, vessels washed in family order, the first rinse off anything silver-bearing collected, surfaces wiped, gloves off by the sequence, and the notebook entry written while it is still in front of you.
• Darkroom opening and closing for a printing sessionARun At the start and the end of every printing session in a darkened roomReview due 2027-09-05The light half of a printing session — the room's certificate read first, the air path opened before the blackout goes up, every stray emitter killed, twenty minutes adapted and the white-paper check passed before the paper box opens, and the reverse at the end.
• Donning, changing and removing protective equipmentARun Before the first cap comes off, whenever a glove is compromised, and at the endReview due 2027-09-05The order that keeps a contaminated outer surface away from skin — apron and eye protection first, gloves last and before the first cap comes off, changed on contact rather than on a schedule, and peeled off so that no bare finger ever touches an outside.
• Night exposure sessionARun Every exposure made after dark, from setting the leave time to being back indoorsReview due 2027-09-05Working after dark with an exposure you computed at home — the leave time fixed before you go, permission asked in daylight, the tripod clear of the passing width, the torch off from the moment the shutter opens, and somebody told when you are back.
• Opening the laboratoryARun At the start of every session, before the first container is openedReview due 2027-09-05The check run at the start of every session before the first container is opened — air, bench, containment, water, vessels, waste, eyewash, spill kit, data sheets, and protective equipment on before the first cap comes off.
• Outdoor exposure sessionARun Every exposure made outdoors in daylight, from leaving the bench to coming back to itReview due 2027-09-05Taking light-sensitive material out into daylight and bringing it back — the hour chosen against the shadow rule, the sun kept off you and out of the optic, the card lifted and replaced around a timer, and the sky written down in words you will use again.
• Plate coating and dryingBRun Coating a bed of prepared glass plates from a melted emulsion and drying themReview due 2027-09-05A bed of prepared glass taken from the melted emulsion to a labelled box — levelled by a puddle of water, fifteen millilitres spread in one pass of a round-bowled spoon, the dry layer cut rather than pulled apart, and the plates dried cool, slow and dust-free.
• Preparing and coating albumen paperARun When a batch of albumen is made, and again a week later when paper is floated on itReview due 2027-09-08Separate the whites completely, salt before beating, whip to froth, rest a day, strain, refrigerate a week — then float, blot the runoff while it dries, and mark the low corner so the second coat can cancel the first one's gradient.
• Print processing: the archival sequenceARun Every print you intend to keep, from the developer tray to dryReview due 2027-09-05A print from the developer tray to dry, at the times and temperatures the makers publish for permanence — short fixing in fresh fixer, the optimum-permanence wash for fibre base, the thirty seconds for resin-coated, and the unexposed control sheet the tests are read on.
• Processing a filmARun Every exposed film, from loading the tank to hanging the dry negativeReview due 2027-09-05One film from a dry reel to a hanging negative — the maker's time, the maker's agitation scheme, the clearing time measured today, the published wash, and the four waste streams the session leaves behind.
• Running a platinum or palladium sessionBRun Coating, exposing, developing and clearing a platinum-group printReview due 2027-09-08Bought solutions only, a dropper calibrated today, equal volumes of iron and metal mixed for one sheet at a time, the developer poured rather than the print lowered, three clearing baths in the order the pH argument sets, and the masked margin read before the wash.
• Running a toning sessionBRun Any evening on which a finished print will be put into a tonerReview due 2027-09-08A matched set printed for the toner, fixed twice in a non-hardening bath and proved washed before anything is toned, then run against an untoned control kept wet beside the tray, with the endpoint recorded rather than remembered.
• Setting up and shutting down the print processing lineARun The first and last twenty minutes of every printing eveningReview due 2027-09-08Five positions laid out in a fixed order with their own tongs, brought into the band and logged before the first sheet, and struck down at the end into labelled containers with the two clocks read and written.
• Solargraph camera placement and retrievalARun Siting a sealed solargraph camera outdoors, and opening it weeks or months laterReview due 2027-09-05Leaving a sealed can outdoors for a season and getting it back — permission asked in daylight, the aim computed from your own latitude, the tape tab logged as the start of the exposure, and the sheet scanned before room light finishes it.
• The printing-out processing lineBRun Every salted-paper, albumen or other printing-out sheet, from the frame to dryReview due 2027-09-08Expose past the point where it looks right, wash until the cloud stops, tone before fixing, fix weak, brief, plain and alkaline, then wash to a sequence and prove it — with no acid anywhere near a thiocyanate toner.
• The student's project SOPBRun Written at the capstone review gate, before the first bath is mixedReview due 2027-09-08The one procedure assembled rather than written — a whole-project hazard assessment, a waste plan, a schedule with its waits, and a contingency rule per failure, all decided at the review gate before the first bath is mixed.
• UV unit operating procedureBRun Every session that energises a UVA exposure unit, from cold to cool-downReview due 2027-09-05One exposure from cold — the label read, the hours counter noted, the interlock proved before anything is coated, the warm-up run, the frame in its battens, the print inspected with the array dark, and the dose logged before the unit is put away.

Waste

• Collecting and segregating waste across a multi-run sessionARun Any session that runs more than one developer, or the same one many times overReview due 2027-09-08Four or five streams from an evening that develops the same film four ways — the alkaline developers apart from the acidic silver-bearing fixer, a staining developer apart from both, and a container per stream standing open from the first pour.
• Routing chromium(III) from the coating stationARun Any session in which chrome alum went into an emulsion or into a dipReview due 2027-09-05Where every rinse goes when chrome alum has been in the session — the syringe that measures nothing else, the dip that is not tipped, the processing water that carries the hardener out of the layer, and the word that has to appear on the label.
• Routing general chemical wasteARun Whenever a spent solution leaves a tray, a tank or a bottleReview due 2027-09-04Getting each spent solution into the container for its own stream — naming the liquid first, keeping acid apart from sulfite and thiosulfate, leaving headspace, topping up the volume line, and taking the route you looked up and dated.
• Routing silver-bearing wasteARun Every session in which silver is dissolved, coated, fixed or washedReview due 2027-09-04Keeping every gram of silver a session produces in one labelled container and out of the drain — spent fixer, the first wash, every rinse off a silver vessel, failed solutions, and the solids that carry silver.
• Segregating alternative-process wasteARun Every alternative-process session, from before the first tray is filledReview due 2027-09-08Five or six streams from one bench, each in its own labelled container with its own funnel, kept apart because two of them are an incompatible pair and two more are worth recovering.