Stop baths compared

Three baths that all do the same job — neutralise the alkali a print or a film carries out of the developer — and differ in the acid, its concentration and its physical form. It is the smallest matrix in this product and the one where the axes do the most work, because two of the three are the same formula at two strengths and the third is the course’s own substitution.

⁇One of these three is not a published formula

The citric bath is this course’s own variant of Kodak’s SB-1, matched proton for proton rather than gram for gram, and it is labelled as a variant everywhere it appears — here, in the formulary and in its own front matter. No manufacturer’s composition is reconstructed in it and nothing on its page tells you anything about any commercial citric stop bath. Where it is scored, the score rests on the same published constants as the arithmetic that produced it; where the course has not tested it, the cell is empty and says so, which is why its capacity and its keeping are both blank.

Stop baths

Kodak's SB-1, its three-times-strength sibling for Reflex plates, and this course's own citric variant, compared on acid load, capacity, keeping, vapour and what each one is published for.

3 subjects on 10 axes. 25 of the 30 cells carry a score with its reasoning and its source; 5 are not established, of which 2 say why for that subject in particular and 3 are answered by their column's own note.

What is in this matrix, and what is not

Three baths that all do one job - neutralise the alkali the material carries out of the developer - and differ in the acid, its concentration and its physical form. Two are Kodak formulas and the third is the course's own variant of SB-1, matched proton for proton rather than gram for gram, and it is marked as a variant everywhere it appears. Nothing here is taken from, or tells you anything about, any commercial stop bath, though the price file prices one and this matrix says where.

Stop baths: every axis against every subject. Each score links to the section that argues it.

Axis	SB-1Kodak, 1949	SB-1afor Reflex plates	Citric variantthe course's own
The acid	Glacial acetic acid	Glacial acetic acid	Citric acid
Acid load	SB-1's load1/2	Three times SB-12/2	SB-1's load1/2
Published capacity	High3/3	Low1/3	—not established
Keeping	Indefinite5/5	Indefinite5/5	—not established
Acid vapour in the room	Yes	Yes	No
Materials it is published for	Film, plates and paper	Film and plates	Film, plates and paper
Complexity	Simple1/4	Simple1/4	Simple1/4
Safety classification	Level B2/4	Level B2/4	Level A1/4
Waste stream	Stop bath stream	Stop bath stream	Stop bath stream
Cost	—not established	—not established	—not established

— not established: the column's own note, or the cell's, says what is missing. * an inference by this course from something a source states, rather than a statement a source makes. Every score in the grid is a link to the paragraph that argues it. 1 of the 10 axes are empty for every subject (Cost), and each of them says why in its own section.

The acid

The question Which acid does the work, and does it arrive as a liquid to be poured or a solid to be weighed?

The scale: The acid, a set of alternatives with no ordering

Which acid does the work, and in what physical form it arrives in the darkroom. It is the axis on which the course's own variant differs from the formula it is based on.

1. Glacial acetic acidA volatile liquid, measured by volume and diluted. The 1928 primer argues it is the best acid for the purpose because its acidity is low for its neutralising capacity.
2. Citric acidA solid, weighed. Three ionisable protons rather than one, so the same acid capacity arrives in a fifth of the moles.

Where a cell is empty The formula does not name its acid, which would make it not a stop bath formula.

SB-1Kodak, 1949

Glacial acetic acidstated by the source

17 mL of glacial acetic acid, about 99.5 per cent, in 1000 mL of water. The 1928 primer argues the choice rather than asserting it: what matters in a stop bath is how much alkali the acid can neutralise, which depends on the total hydrogen present, while the acidity depends on how much of that hydrogen is dissociated - and acetic acid is therefore the best acid for the purpose.

Sources:Kodak Limited, 1949§ Kodak formula SB-1, acid stop bath for papers, plates and films, metric column · Eastman Kodak Company, 1928§ Chapter IV, the design rule that acidity depends on dissociated hydrogen while neutralising capacity depends on total hydrogen

Argued in:SB-1, function of every ingredient

SB-1afor Reflex plates

Glacial acetic acidstated by the source

The same glacial acetic acid at 50 mL a litre. Kodak changes the concentration and not the acid, which is what makes SB-1 and SB-1a a controlled pair: everything that differs between them is the quantity.

Sources:Kodak Limited, 1949§ Kodak formula SB-1A, acid stop bath for Reflex plates, metric column

Argued in:SB-1a, function of every ingredient

Citric variantthe course's own

Citric acidstated by the source

19.2 g of anhydrous citric acid made up to a litre - a solid that is weighed rather than a volatile liquid that is poured. The substitution is the course's own and is published as a variant with its arithmetic shown, not attributed to any manufacturer.

Sources:Prepared by an international group of experts on behalf of the International Labour Organization and the World Health Organization, with the financial assistance of the European Commission, 1998§ Molecular mass 192.1; solubility 59 g per 100 mL of water at 20 degrees C; chemical dangers · International Union of Pure and Applied Chemistry, Dissociation Constants project; digitised from the Serjeant and Dempsey and Perrin compilations, 2024§ Entry serjeant2865, citric acid, pKa1 2.87, pKa2 4.35 and pKa3 5.68

Argued in:The citric variant, and what it is based on

Acid load

The question How much titratable acid does a litre carry, against SB-1 as the reference?

The scale: Acid load, ordered

The titratable acid a litre of the bath carries, against Kodak's SB-1 as the reference point. A stop bath's job is to neutralise the alkali a print or a film carries into it, so capacity is acid quantity rather than acid strength.

1. 1SB-1's loadAbout 0.30 mol of titratable protons per litre, which is what 17 mL of glacial acetic acid delivers.
2. 2Three times SB-1Three times that concentration, published for a material that carries three times as much alkali into the bath.

Where a cell is empty The source gives no quantity, so the bath's neutralising capacity cannot be placed.

SB-1Kodak, 1949

SB-1's loadposition 1 of 2stated by the source

17 mL of glacial acetic acid a litre is about 0.30 mol of acetic acid, and acetic acid has one ionisable proton, so the bath carries about 0.30 mol of titratable protons per litre. That figure is the reference the other two baths in this matrix are measured against.

Sources:Kodak Limited, 1949§ Kodak formula SB-1, metric column · International Union of Pure and Applied Chemistry, Dissociation Constants project; digitised from the Serjeant and Dempsey and Perrin compilations, 2024§ Entry serjeant2043, acetic acid, pKa1 4.76 at 25 degrees C

Argued in:The proton arithmetic, worked

SB-1afor Reflex plates

Three times SB-1position 2 of 2stated by the source

50 mL a litre, three times SB-1's concentration, and Kodak's reason is on the face of the formula: it follows the high-alkali developer D-8, so three times as much alkali arrives in the bath and three times the acid is there to meet it. A stop bath's capacity is a quantity of acid, not a pH.

Sources:Kodak Limited, 1949§ Kodak formula SB-1A, acid stop bath for Reflex plates, metric column

Argued in:SB-1a, purpose

Citric variantthe course's own

SB-1's loadposition 1 of 2stated by the source

Matched to SB-1 on titratable protons rather than on mass or volume: citric acid has three ionisable protons, so 0.100 mol of it - 19.2 g at 192.12 g/mol - carries the same 0.300 mol that SB-1's acetic acid does. It is made up to volume rather than added to a litre of water, because a molarity match is what is being claimed.

Sources:International Union of Pure and Applied Chemistry, Dissociation Constants project; digitised from the Serjeant and Dempsey and Perrin compilations, 2024§ Entry serjeant2865, citric acid, pKa1 2.87, pKa2 4.35 and pKa3 5.68; entry serjeant2043, acetic acid, pKa1 4.76 · Prepared by an international group of experts on behalf of the International Labour Organization and the World Health Organization, with the financial assistance of the European Commission, 1998§ Molecular mass 192.1

Argued in:The proton arithmetic, worked

Published capacity

The question How much material does the source publish for a made-up volume before the bath stops being acid?

The scale: Published capacity, ordered

How much material the maker publishes for a made-up volume. The bases differ between sources, so every cell gives the figure and the volume it is per.

1. 1LowA small published figure, or one deliberately held down for a reason the cell states.
2. 2ModerateThe ordinary published figure for its class.
3. 3HighAt or near the top of the maker's own table for baths of its kind.

Where a cell is empty No capacity is published for this bath, and none can be derived from another formula's. The 1928 primer's litmus test is the substitute: a rinse bath that no longer turns litmus is finished, whatever the count says.

SB-1Kodak, 1949

Highposition 3 of 3stated by the source

90 sheets of 8 by 10 inches per 160 imperial fluid ounces in a dish or a deep tank, and the 1928 primer gives the print figure from the other direction: roughly seventy-five 8 by 10 prints per US gallon with a one-to-two-second drain from a typical Elon-hydroquinone developer, before the bath turns alkaline. Two sources, two bases, the same order of magnitude.

Sources:Kodak Limited, 1949§ The useful-life row giving SB-1 90 sheets of 8 by 10 inches per 160 fl.oz. · Eastman Kodak Company, 1928§ Rinsing Prints, the capacity of the acid rinse bath and the litmus test for whether it is still acid

Argued in:SB-1, behaviour

SB-1afor Reflex plates

Lowposition 1 of 3stated by the source

40 sheets of 8 by 10 inches per 160 imperial fluid ounces, used after D-8 - less than half SB-1's figure from three times the acid. That is not a contradiction: the developer it follows carries so much more alkali per sheet that trebling the acid still leaves the bath exhausted sooner.

Sources:Kodak Limited, 1949§ Table of keeping properties and useful life of solutions, SB-1A row

Argued in:SB-1a, behaviour

Citric variantthe course's own

Not established

No capacity is published or claimed. The substitution is matched to SB-1 on titratable protons by arithmetic, and a matched proton load is a reason to expect a similar capacity rather than a measurement of one: the two acids differ in how their protons come off, citric acid being triprotic with pKa values of 2.87, 4.35 and 5.68 against acetic acid's single 4.76. Capacity and the shape of the exhaustion curve are precisely what Part X's own experiment is built to test, and it has not been performed.

Sources:International Union of Pure and Applied Chemistry, Dissociation Constants project; digitised from the Serjeant and Dempsey and Perrin compilations, 2024§ Entry serjeant2865, citric acid, pKa1 2.87, pKa2 4.35 and pKa3 5.68; entry serjeant2043, acetic acid, pKa1 4.76

Argued in:The citric variant, behaviour

Keeping

The question What keeping does the source publish, standing in a dish, in a tank and bottled?

The scale: Keeping, ordered

The longest keeping figure the maker publishes for the solution in a full, closed bottle. The cell gives the shorter working figures with it.

1. 1HoursPublished in hours: a bath made for the session it is used in.
2. 2DaysPublished in days.
3. 3WeeksPublished in weeks.
4. 4MonthsPublished in months in a full stoppered bottle; the half-filled figure is always shorter and is given in the cell.
5. 5IndefiniteThe maker's own word. It keeps until something contaminates it.

Where a cell is empty The source publishes no keeping figures for the bath.

SB-1Kodak, 1949

Indefiniteposition 5 of 5stated by the source

Kodak's own word for the bottled bath is indefinite, full or half full, which no other solution in this reference is given. Three days standing in a dish and a month in a tank are the working figures, and the difference between them and the bottle is contamination rather than decomposition: there is nothing in dilute acetic acid to oxidise.

Sources:Kodak Limited, 1949§ Table of keeping properties and useful life of solutions, SB-1 row

Argued in:SB-1, storage

SB-1afor Reflex plates

Indefiniteposition 5 of 5stated by the source

The same row as SB-1: indefinite in a stoppered bottle full or half full, three days in a dish, a month in a tank. Three times the acid changes the capacity and not the keeping.

Sources:Kodak Limited, 1949§ Table of keeping properties and useful life of solutions, SB-1A row

Argued in:SB-1a, storage

Citric variantthe course's own

Not established

The page publishes none and refuses to borrow SB-1's. Kodak's indefinite keeping for a bottled acid shows that oxidation is not the limit for an acid bath, so whatever limits a citrate solution is something else - and the course could find no manufacturer sheet, safety data sheet or reference work that establishes it. ILFORD's seven working days at working strength is the nearest published figure and belongs to a different product with an indicator dye in it. The instruction on the page is therefore to date the bottle, inspect it and discard anything cloudy.

Sources:HARMAN technology Limited (ILFORD Photo), 2017§ ILFOSTOP storage and solution life, five years in full airtight bottles and seven working days at working strength · Kodak Limited, 1949§ Table of keeping properties and useful life of solutions, SB-1 row

Argued in:The citric variant, storage

Acid vapour in the room

The question Does the acid in this bath evaporate into the darkroom at working temperature, and does a source quantify it?

This is the axis the course's own variant exists for, and it is the one place in this matrix where the three baths are not doing the same thing to the room.

The scale: Does the source say so, a set of alternatives with no ordering

For an axis that asks a plain question of the evidence. Yes and no are both statements a source makes; a source that says nothing produces an unscored cell instead.

1. YesA source states it.
2. Yes, with a conditionA source states it and attaches a condition, which the cell gives.
3. NoA source states the opposite.

Where a cell is empty No source in the corpus addresses the volatility of this bath's acid.

SB-1Kodak, 1949

Yesstated by the source

Glacial acetic acid is volatile, and the vapour is what makes the bottle rather than the tray the hazard in this bath: the international chemical safety card gives the physical and chemical dangers for the concentrated acid, and the acid is measured by volume from that bottle in the darkroom.

Sources:Prepared by an international group of experts on behalf of the International Labour Organization and the World Health Organization, with the financial assistance of the European Commission, 2010§ Physical dangers; routes of exposure; inhalation risk

Argued in:SB-1, safety

SB-1afor Reflex plates

Yesstated by the source

Three times the acetic acid in the same volume of water, from the same bottle of glacial acid, and the same inhalation route. Whatever is true of SB-1 in a small room is true of SB-1a more so, which is the strongest practical argument in this matrix for the citric substitution.

Sources:Prepared by an international group of experts on behalf of the International Labour Organization and the World Health Organization, with the financial assistance of the European Commission, 2010§ Physical dangers; routes of exposure; inhalation risk

Argued in:SB-1a, safety

Citric variantthe course's own

Nostated by the source

The international chemical safety card for citric acid states negligible evaporation at 20 degrees C. There is no bottle of volatile concentrate in the room, because the acid arrives as a weighed solid; the hazard moves to the powder, and the same card records that a dust explosion is possible if the powder or granules are mixed with air, with explosive limits of 0.28 to 2.29 volume per cent.

Sources:Prepared by an international group of experts on behalf of the International Labour Organization and the World Health Organization, with the financial assistance of the European Commission, 1998§ Negligible evaporation at 20 degrees C; the dust explosion statement and its explosive limits; MAK 2 mg/m3 for the inhalable fraction

Argued in:The citric variant, safety

Materials it is published for

The question Which materials does the source publish this bath for?

The scale: Materials it is published for, a set of alternatives with no ordering

Which materials the maker publishes the formula for. It is a statement about the document, not a judgement about what would happen if you used it elsewhere.

1. Film and platesPublished for negative materials only.
2. Film, plates and paperPublished for negative materials and for prints.
3. PaperPublished for prints only.
4. Paper and hand-coated processesPublished for prints, including hand-coated and printing-out papers.

Where a cell is empty The source does not say what the bath is for.

SB-1Kodak, 1949

Film, plates and paperstated by the source

Kodak's header is an acid stop bath for papers, plates and films, and the handbook's instruction is a five-second rinse for prints. One bath across three materials, which is what a stop bath's job allows: it is neutralising an alkali rather than acting on an emulsion.

Sources:Kodak Limited, 1949§ Kodak formula SB-1, header, metric column, with prints rinsed for 5 seconds

Argued in:SB-1, recommended uses

SB-1afor Reflex plates

Film and platesstated by the source

Kodak's header names Reflex plates specifically, and the formula exists because of the developer those plates were processed in rather than because of the plates themselves. It is the narrowest scope in this matrix and the clearest case of a formula written for one workflow.

Sources:Kodak Limited, 1949§ Kodak formula SB-1A, acid stop bath for Reflex plates, header and metric column

Argued in:SB-1a, recommended uses

Citric variantthe course's own

Film, plates and paperstated by the source

The variant inherits SB-1's scope because it is matched to SB-1's acid load, and the course states the inheritance rather than leaving it implied. What it does not inherit is SB-1's capacity figure, which is a separate claim and is not made.

Sources:Kodak Limited, 1949§ Kodak formula SB-1, header - for papers, plates and films

Argued in:The citric variant, recommended uses

Complexity

The question What does making this bath actually demand of the person making it?

The scale: Complexity to make and work, ordered

What mixing and using the formula actually demands: how many things are weighed, whether order and temperature matter, and whether the bath has to be made in parts or ripened before use.

1. 1SimpleA handful of solids into water in a stated order, at room temperature, used straight away.
2. 2ModerateSeveral solids, an order that matters and a stated dissolving temperature, or a stock that is diluted before use.
3. 3InvolvedTwo or more solutions to mix separately and combine correctly, a hot bath, or a ripening period before the formula works.
4. 4SpecialistNeeds equipment, control or handling beyond a domestic laboratory, and the course says so on the page.

Where a cell is empty The source publishes no mixing instruction.

SB-1Kodak, 1949

Simpleposition 1 of 4stated by the source

17 mL of acid into a litre of water, in that order, which is the one rule that matters: acid into water and never the reverse. There is nothing to dissolve, nothing to heat and no order beyond that one.

Sources:Kodak Limited, 1949§ Kodak formula SB-1, metric column and mixing instruction

Argued in:SB-1, mixing

SB-1afor Reflex plates

Simpleposition 1 of 4stated by the source

50 mL of acid into a litre of water, and the same single rule. Measuring three times as much glacial acid is three times as much handling of the concentrate, which is a safety difference rather than a difficulty one.

Sources:Kodak Limited, 1949§ Kodak formula SB-1A, metric column and mixing instruction

Argued in:SB-1a, mixing

Citric variantthe course's own

Simpleposition 1 of 4stated by the source

19.2 g weighed and made up to a litre. It needs a balance where SB-1 needs a measuring cylinder, which is the one practical difference, and citric acid dissolves readily at 59 g per 100 mL of water at 20 degrees C so nothing has to be warmed.

Sources:Prepared by an international group of experts on behalf of the International Labour Organization and the World Health Organization, with the financial assistance of the European Commission, 1998§ Solubility 59 g per 100 mL of water at 20 degrees C

Argued in:The citric variant, mixing

Safety classification

The question What is the course's hazard-assessed level for this bath, and which substance sets it?

The scale: Safety classification, ordered

The course's own hazard-assessed classification for the formula or process, from the safety library. The cell names the substance that sets it.

1. 1Level ADomestic-scale care. No specialist control is required by the substances themselves.
2. 2Level BGloves, eye protection and ventilation as stated; a sensitiser, an irritant or a dust that must not be breathed.
3. 3Level CA serious hazard with a named control; restricted procedures, and never a first session.
4. 4Level DStudied and never performed at home. The course gives the chemistry, the history and the hazards, and no procedure.

Where a cell is empty The bath has not been classified. Every formula in this course carries a level, so an empty cell here would be a fault rather than a finding about the evidence.

SB-1Kodak, 1949

Level Bposition 2 of 4stated by the source

The bath is dilute and the bottle is not. Glacial acetic acid at about 99.5 per cent is corrosive and volatile, and it is measured in the darkroom, which is what puts the formula past Level A - the diluted working bath on its own would not.

Sources:Prepared by an international group of experts on behalf of the International Labour Organization and the World Health Organization, with the financial assistance of the European Commission, 2010§ Physical dangers, chemical dangers, routes of exposure and effects of short-term exposure for the glacial acid

Argued in:SB-1, safety

SB-1afor Reflex plates

Level Bposition 2 of 4stated by the source

The same classification for the same reason, at three times the volume of concentrate handled per litre made. The level is set by the operation of measuring the glacial acid rather than by the strength of the bath that results.

Sources:Prepared by an international group of experts on behalf of the International Labour Organization and the World Health Organization, with the financial assistance of the European Commission, 2010§ Physical dangers, chemical dangers and routes of exposure for the glacial acid

Argued in:SB-1a, safety

Citric variantthe course's own

Level Aposition 1 of 4stated by the source

Citric acid's aggregated classification from 4,373 ECHA reports is eye irritation at 84.7 per cent of notifications and respiratory irritation at 23 per cent, with 359 of those reports stating that it meets no GHS hazard criterion at all - against a corrosive volatile liquid. The controls become dust control at the balance and eye protection, which is a Level A profile.

Sources:National Center for Biotechnology Information§ GHS classification aggregated from 4373 ECHA C&L reports, H319 at 84.7 per cent and H335 at 23 per cent · Prepared by an international group of experts on behalf of the International Labour Organization and the World Health Organization, with the financial assistance of the European Commission, 1998§ MAK 2 mg/m3 for the inhalable fraction; the dust explosion statement

Argued in:The citric variant, safety

Waste stream

The question Which stream does the spent bath belong to?

The scale: Waste route, a set of alternatives with no ordering

Which of the five streams that leave a silver darkroom this bath belongs to. They are kept apart because they are chemically incompatible and have different destinations, and that much is a consequence of reactions rather than of statutes. What may lawfully be done with any of them depends on where you are.

1. Developer streamAlkaline, organic and oxygen-demanding. Its own labelled container, and never mixed with the fixer bottle, which would ruin a recoverable solution.
2. Stop bath streamAcid. Its own container: acid meeting a sulfite or a thiosulfate liberates sulfur dioxide at once.
3. Fixer and silver streamThiosulfate carrying dissolved silver, at thousands of milligrams per litre. It never goes to a drain and it is the stream silver recovery exists for.
4. Hazardous collection onlyA heavy metal, a sulfide or a cyanide bath. The whole volume is a collected waste and no part of it is a drain question.

Where a cell is empty The waste chemistry of the bath has not been established.

SB-1Kodak, 1949

Stop bath streamstated by the source

Spent stop bath is the acid stream and is kept in its own container for a reason that is chemistry rather than regulation: acid meeting a sulfite or a thiosulfate liberates sulfur dioxide at once, and thiosulfate also throws down sulfur. The bath carries no silver of its own.

Sources:Eastman Kodak Company, 1999§ Properly dispose of photographic processing chemicals; keeping streams separate

Argued in:SB-1, waste · The disposal caveat

SB-1afor Reflex plates

Stop bath streamstated by the source

The same stream at three times the acid concentration, which matters when the container is opened rather than when it is filled. Nothing acid goes into the developer or fixer bottle, and a stronger acid makes that rule no more or less absolute.

Sources:Eastman Kodak Company, 1999§ Properly dispose of photographic processing chemicals; keeping streams separate

Argued in:SB-1a, waste · The disposal caveat

Citric variantthe course's own

Stop bath streamstated by the source

The acid stream, and the same incompatibility rule: a citric bath liberates sulfur dioxide from a sulfite exactly as an acetic one does, because the reaction belongs to the proton and not to the acid it came from. The organic load is higher, since citric acid is a larger molecule at a comparable molarity.

Sources:Eastman Kodak Company, 1999§ Properly dispose of photographic processing chemicals; keeping streams separate · Prepared by an international group of experts on behalf of the International Labour Organization and the World Health Organization, with the financial assistance of the European Commission, 1998§ Chemical dangers, that the solution in water is a medium strong acid and attacks metals

Argued in:The citric variant, waste · The disposal caveat

Cost

The question What does a litre of this bath cost to mix from raw chemicals, on the dated UK prices behind the laboratory planner?

The priced product is in the file as stop-bath. It tells a reader what a bottle costs and tells this matrix nothing, which is the distinction the column is here to keep.

The scale: Cost, ordered

The course's relative cost band for mixing a litre from raw chemicals, on the dated UK prices in the price file behind the laboratory planner. The bands are relative and the course defines no money threshold for them, so every cell gives the priced subtotal it rests on and names the ingredients the price file could not price.

1. 1£The cheapest band: bulk photographic chemicals, in doses of a few grams to a hundred grams a litre.
2. 2££The ordinary band. Several bulk chemicals, or one bought in a small jar at a laboratory price.
3. 3£££One ingredient dominates the cost, and it is usually a silver salt.
4. 4££££A noble metal at working strength. The chemistry is a significant purchase in itself.

Where a cell is empty The price file holds no price for glacial acetic acid or for citric acid as a raw chemical. What it does price is a ready-made 500 mL citric stop-bath concentrate at 10.66 to 12.18 in sterling, diluted 1+19 - a product rather than a formula, and not a figure any of these three baths can be costed from. The column stays empty until the file prices the acids themselves.

SB-1Kodak, 1949

Not established

Nothing specific to this subject to add: the column’s own note above is the whole answer.

SB-1afor Reflex plates

Not established

Nothing specific to this subject to add: the column’s own note above is the whole answer.

Citric variantthe course's own

Not established

Nothing specific to this subject to add: the column’s own note above is the whole answer.