Printing processes compared

The process atlas already sets these seven side by side in prose. What this page adds is a position on a declared scale for each one, with the reasoning under it — which turns a description into something a student can use to decide what to shoot before they decide what to print. The column that does most of that work is what it asks of the negative, because six of the seven cannot be enlarged at all and three of those want a negative that a normal darkroom does not produce.

!This is not the comparison the design ultimately asks for

Brief section 31 asks for one negative printed across seven processes in one darkroom. Nobody has printed it: the standard negative belongs to Part XXI and the comparison itself to a Part XXV assignment, and neither part is written. A comparison assembled from different photographers, papers, negatives and decades tells you what the processes are like; it does not tell you what they do to the same picture. Everything below is the first kind.

Printing processes

The seven processes brief section 31 names, scored on what each asks of the negative, what it gives back, what decides its permanence and what it costs - with the cell that cannot be filled left open.

7 subjects on 10 axes. 67 of the 70 cells carry a score with its reasoning and its source; 3 are not established, of which 3 say why for that subject in particular and 0 are answered by their column's own note. 3 scored cells are marked inferred, meaning the course reasoned them out of something a source states rather than reading them off it.

What is in this matrix, and what is not

The seven processes the design names for its comparison: silver gelatin, cyanotype, salted paper, albumen, kallitype, Van Dyke Brown, and palladium in place of platinum, which is the course's own substitution of 4 September 2026 on the ground that students perform palladium and never handle platinum. This matrix is the second of two comparisons and not the first. The process atlas already sets these seven side by side in prose from the published literature; what this adds is a position on a declared scale for each one, with the reasoning under it. Neither is the comparison the design ultimately asks for, which is one negative printed in seven processes in one darkroom. That comparison is now written as an assignment - Part XXV's process comparison atlas sets it, and Part XXII's printing lab produces the salted-paper row of it from a standard negative, as Part XXI's produces the cyanotype row - but nobody has returned a completed set, so every row below is still assembled from different photographers, different papers and different decades, and no column here is a substitute for one darkroom's measurements. When a student does return one, the rows that change are the ones this scope note is warning about.

Printing processes: every axis against every subject. Each score links to the section that argues it.

Axis	Silver gelatinfibre base	Cyanotypeclassic	Salted paper	Albumen	Kallitype	Van Dyke Brown	Palladiumfor platinum
How the image arrives	Developing out	Printing out	Printing out	Printing out	Developing out	Printing out	Developing out
Light it needs	Either	Ultraviolet	Ultraviolet	Ultraviolet	Ultraviolet	Ultraviolet	Ultraviolet
What it asks of the negative	Any negative, enlarged or contacted	Contact, ordinary scale	Contact, long scale	Contact, long scale	Contact, ordinary scale	Contact, long scale	Contact, long scale
Tonal scale	Moderate2/3	Short1/3	Long3/3	Long3/3	Moderate2/3	Long3/3	Long3/3
Image colour	Neutral to warm	Prussian blue	Purple-brown	Purple-brown	Set in the developer	Warm brown	Warm brown
Surface	Emulsion over baryta	In the fibres, matte	In the fibres, matte	In a binder, glossy	In the fibres, matte	In the fibres, matte	In the fibres, matte
What decides permanence	Processing decides it	Ordinary conditions attack it	Processing decides it	Ordinary conditions attack it	Processing decides it	Processing decides it	The metal decides it
Difficulty	Moderate2/4	Low1/4	Moderate2/4	High3/4	High3/4	Moderate2/4	High3/4
Safety classification	Level A1/4	Level B2/4	Level B2/4	Level B2/4	Level B2/4	Level B2/4	Level B2/4
Cost	££2/4*, an inference by this course	£1/4	££2/4*, an inference by this course	££2/4*, an inference by this course	—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.

How the image arrives

The question Does light make the visible image directly, or an invisible one that a developer amplifies?

The scale: How the image arrives, a set of alternatives with no ordering

Whether light makes the whole image or only a latent one that a developer then amplifies. It is the largest single difference between the processes in this atlas.

1. Printing outLight makes the visible image directly. Reilly puts the light energy needed at up to 100,000 times that of developing out.
2. Developing outLight makes an invisible latent image and a developer amplifies it.

Where a cell is empty The course has not established how the image is formed, which for a process in this atlas would be a fault.

Silver gelatinfibre base

Developing outstated by the source

A developing-out paper: the exposure makes a latent image and the developer amplifies it. Reilly's figure is the one that makes the difference concrete - printing out needs up to 100,000 times the light energy of developing out, which is why this is the only process in the matrix that can be printed under an enlarger in a room.

Sources:American Institute for Conservation, Photographic Materials Group§ Identification characteristics - the image within the emulsion layer, on top of the baryta layer in developing-out papers · James M. Reilly, 1980§ Chapter One, Printing-out papers, and the light energy comparison

Argued in:Silver gelatin, the chemistry

Cyanotypeclassic

Printing outstated by the source

Light reduces iron(III) to iron(II) in the coating and the iron(II) then makes Prussian blue: the image is visible when the exposure ends and there is no developer at all. Ware's classic formula runs 20 to 30 minutes in sunlight or under a UV lamp.

Sources:Mike Ware, 2020§ 3.7 Chemistry of blueprinting; 7.1 Classic cyanotype sensitizer, preparation, exposure and wet processing · John Frederick William Herschel, 1842§ Articles 202 to 213: ferrosesquicyanuret paper and the two stages

Argued in:Cyanotype, the chemistry

Salted paper

Printing outstated by the source

Printed out by inspection under the negative: the silver chloride in the paper is reduced by light to the colloidal silver that is the image, and the print is watched rather than timed. Reilly's up-to-100,000-times figure is what confines it to contact printing.

Sources:Dusan C. Stulik and Art Kaplan, 2013§ Process description; Visual characteristics · James M. Reilly, 1980§ Chapter One, Printing-out papers; Classification of printing-out papers

Argued in:Salted paper, the chemistry

Albumen

Printing outstated by the source

The same printing-out silver chemistry as the salted paper, carried in a protein layer on the surface rather than in the fibres. Printed out by inspection under a negative, and toned in gold before fixing rather than after it.

Sources:Dusan C. Stulik and Art Kaplan, 2013§ Process description; Visual characteristics · American Institute for Conservation, Photographic Materials Group§ Process description; identification characteristics

Argued in:Albumen, the chemistry

Kallitype

Developing outstated by the source

The one alternative process in this matrix that develops out. Light reduces iron(III) to iron(II) and the developer is where the iron(II) reduces the silver, so the exposure is carried much further by the developer than by the light - and the image colour is set in the developer rather than in the coating.

Sources:Photographers' Formulary§ The three development formulas and their times and temperatures; the note on how the proportion of A to B moves the image colour · Mike Ware§ The siderotype family and where the silver is reduced

Argued in:Kallitype, the chemistry

Van Dyke Brown

Printing outstated by the source

Printing out under ultraviolet, so there is no developer and no test strip is strictly needed: the print is watched. It is the same iron-silver chemistry as the kallitype with the reduction happening during the exposure rather than in a tray, which is the whole difference between the two.

Sources:Mike Ware§ An alternative silver salt; the printing-out behaviour of the ferric-silver system · Photographers' Formulary, with safety data sheets from Columbus Chemical Industries and other suppliers§ Mixing the solutions - the sensitizer

Argued in:Van Dyke Brown, the chemistry

Palladiumfor platinum

Developing outstated by the source

Developed out in a citrate or oxalate bath, where the iron(II) made by the exposure reduces the palladium salt to the metal. Palladium prints faster than platinum because more of it is aquated at sensitiser strength, which is Ware's account and the reason the course teaches palladium.

Sources:Mike Ware, 2017§ 11.7 aquation of the tetrachlorometallate anions; 11.8 stoichiometry; Willis's palladiotype developer · Photographers' Formulary, Inc.§ The division of labour between ferric oxalate and the palladium salt

Argued in:Palladium, the chemistry

Light it needs

The question What part of the spectrum exposes the sensitised material?

The scale: Light it needs, a set of alternatives with no ordering

What part of the spectrum exposes the material, which decides whether an enlarger can print it at all.

1. VisibleExposed by visible light.
2. UltravioletExposed by near ultraviolet: sunlight or a UV source, and a contact frame.
3. EitherSensitive enough in the visible to be printed under an enlarger, and printable by contact as well.

Where a cell is empty The spectral sensitivity of the material has not been established.

Silver gelatinfibre base

Eitherstated by the source

A manufactured emulsion sensitive well into the visible, which is what makes an enlarger possible and a safelight necessary. It is the only process in this matrix that can be printed either by enlargement or by contact, and the only one whose exposure is measured in seconds.

Sources:HARMAN technology Limited, 2013§ Paper structure and finishes; processing times · HARMAN technology Limited (ILFORD Photo), 2010§ Safelight recommendations for variable contrast papers

Argued in:Silver gelatin, the image

Cyanotypeclassic

Ultravioletstated by the source

Near ultraviolet: sunlight or a UV source, and a contact frame. Ware's classic formula runs 20 to 30 minutes, which is a working exposure rather than a limitation, and it is why the process needs no darkroom and no safelight - only a room the sun is not in.

Sources:Mike Ware, 2020§ 7.1 Classic cyanotype sensitizer, preparation, exposure and wet processing

Argued in:Cyanotype, the image

Salted paper

Ultravioletstated by the source

Ultraviolet, by contact, printed out by inspection. The sensitivity is low enough that the printing frame goes into the sun or under a bank of tubes and is opened to look at the print, which is a way of working rather than an inconvenience.

Sources:Dusan C. Stulik and Art Kaplan, 2013§ Process description · James M. Reilly, 1980§ Chapter One, Printing-out papers

Argued in:Salted paper, the image

Albumen

Ultravioletstated by the source

Ultraviolet, by contact, printed out under the negative. The albumen layer does not change the spectral question; it changes where the image sits and what the print looks like.

Sources:Dusan C. Stulik and Art Kaplan, 2013§ Process description

Argued in:Albumen, the image

Kallitype

Ultravioletstated by the source

Contact printing under ultraviolet. The iron(III) salt is what the light acts on, and iron(III) organic salts absorb in the near ultraviolet, which is the property the whole siderotype family is built on.

Sources:Mike Ware§ The photochemistry of iron(III) organic salts · Photographers' Formulary§ Kit contents and exposure

Argued in:Kallitype, the image

Van Dyke Brown

Ultravioletstated by the source

Ultraviolet, by contact. Same iron(III) photochemistry as the kallitype and the cyanotype, and the same consequence: a negative the size of the print, and an exposure measured in minutes rather than seconds.

Sources:Mike Ware§ The ferric-silver system and its exposure · Mike Ware§ The photochemistry of iron(III) organic salts

Argued in:Van Dyke Brown, the image

Palladiumfor platinum

Ultravioletstated by the source

Ultraviolet, by contact, with the ferric oxalate doing the absorbing. Ware's account of why palladium prints faster than platinum is about the aquation of the metal salt rather than about the light, so the exposure remains a UV contact exposure either way.

Sources:Mike Ware, 2017§ 11.7 aquation of the tetrachlorometallate anions · Dusan C. Stulik and Art Kaplan, 2013§ Process description

Argued in:Palladium, the image

What it asks of the negative

The question Can this process be enlarged, and what density range does its negative have to carry?

No cell in this column carries a number, and that is the honest state of it. The atlas establishes the demand in words - self-masking, wants a long density range, prints flat on a negative made for enlarging paper - and nothing in the corpus turns that into a density range, because the standard negative belongs to Part XXI and has not been made.

The scale: What it asks of the negative, a set of alternatives with no ordering

Whether the process can be enlarged at all, and what density range its negative has to carry. It is the axis that decides what a student has to shoot before they can print.

1. Any negative, enlarged or contactedSensitive to visible light, so a small negative can be enlarged onto it.
2. Contact, ordinary scaleA contact-sized negative, of a density range the process's own developer or filtration can accommodate.
3. Contact, long scaleA contact-sized negative of long density range. A negative made for enlarging paper prints flat.

Where a cell is empty The course has not established what the process asks of a negative.

Silver gelatinfibre base

Any negative, enlarged or contactedstated by the source

Any negative, at any size, because the paper is sensitive in the visible and can be enlarged onto. The contrast is not asked of the negative either: it is set by paper grade or by variable-contrast filtration, which is a control the other six processes do not have.

Sources:HARMAN technology Limited (ILFORD Photo), 2010§ Contrast control for variable contrast papers · HARMAN technology Limited, 2013§ Paper structure and finishes

Argued in:Silver gelatin, the image

Cyanotypeclassic

Contact, ordinary scalestated by the source

Contact only, and the odd one out among the alternative processes here: the classic sensitiser has a short exposure scale - Ware gives about 0.9, against about 2.2 for New Cyanotype - so it wants a negative of ordinary range rather than a long one. A long-scale negative made for a salted paper print will lose its highlights in a classic cyanotype.

Sources:Mike Ware, 2020§ 7.2.3 Shortcomings of the Classic cyanotype process; the exposure scale of the classic sensitiser against New Cyanotype

Argued in:Cyanotype, the image

Salted paper

Contact, long scalestated by the source

Contact only, and it wants a negative of long density range: the print-out image is self-masking, so density already laid down slows further darkening and the process accommodates a long-range negative by exposing longer. On a negative made for enlarging paper it prints flat.

Sources:James M. Reilly, 1980§ Chapter One, Printing-out papers; the self-masking behaviour of print-out images · Dusan C. Stulik and Art Kaplan, 2013§ Visual characteristics

Argued in:Salted paper, the image

Albumen

Contact, long scalestated by the source

Contact only, and the same long print-out scale as the salted paper with cleaner highlights and more apparent sharpness from the same negative. The albumen layer holds the image above the fibres, which is what buys the highlight separation.

Sources:Dusan C. Stulik and Art Kaplan, 2013§ Visual characteristics; the gloss and its reception · James M. Reilly, 1980§ Chapter 2, the role of organic binders

Argued in:Albumen, the image

Kallitype

Contact, ordinary scalestated by the source

Contact only, and the scale is set in the developer rather than in the coating - which is what distinguishes it from every print-out process in this matrix. The proportion of the two developer stocks moves both the colour and the contrast, so the negative's range is met by the tray rather than by the exposure.

Sources:Photographers' Formulary§ The three development formulas; the note on how the proportion of A to B moves the image colour · Photographers' Formulary, Inc.§ The 20 per cent sodium citrate developer and its replenishment

Argued in:Kallitype, the image

Van Dyke Brown

Contact, long scalestated by the source

Contact only, with a long self-masking print-out scale: density already laid down slows further darkening, so a longer density range in the negative is accommodated by exposing longer. The demand is the salted paper's demand, in a different chemistry.

Sources:Mike Ware§ The printing-out behaviour of the ferric-silver system · Mike Ware, 2019§ 5.10 Siderotype processes

Argued in:Van Dyke Brown, the image

Palladiumfor platinum

Contact, long scalestated by the source

Contact only, and usually a little longer in scale than platinum and lower in contrast from the same negative - which means contrast has to be put back deliberately with an oxidant. The chlorate contrast agent in the kit is that control, and it is the reason the demand on the negative is a range rather than a fixed target.

Sources:Photographers' Formulary, Inc.§ The potassium chlorate contrast agent and its mechanism · Bostick & Sullivan, Inc.§ The chlorate comparison between platinum and palladium

Argued in:Palladium, the image

Tonal scale

The question How long a range of tones does the process hold, and what sets it?

The scale: Tonal scale, ordered

How long a range of subject tones the process can hold, which is the same question as what density range its negative should have.

1. 1ShortA short scale that a long-range negative will not fit; the cell gives the figure where one is published.
2. 2ModerateAn ordinary printing scale, or one set by a grade or a filter rather than by the process.
3. 3LongA long, usually self-masking scale that wants a negative of long density range.

Where a cell is empty The tonal scale of the process has not been established.

Silver gelatinfibre base

Moderateposition 2 of 3stated by the source

Set by paper grade or by variable-contrast filtration rather than by the emulsion alone, which makes the scale a choice rather than a property. It is the only entry in this column whose value is decided after the negative is made.

Sources:HARMAN technology Limited (ILFORD Photo), 2010§ Contrast control for ILFORD MULTIGRADE variable contrast papers

Argued in:Silver gelatin, the image

Cyanotypeclassic

Shortposition 1 of 3stated by the source

Short, and Ware gives the figure: an exposure scale of about 0.9 for the classic sensitiser against about 2.2 for New Cyanotype. It is the only number in this whole column, and it is the reason the classic process has a reputation for losing its highlights that the chemistry rather than the printer earns.

Sources:Mike Ware, 2020§ 7.2.3 Shortcomings of the Classic cyanotype process

Argued in:Cyanotype, the image

Salted paper

Longposition 3 of 3stated by the source

A long, self-masking print-out scale. The self-masking is the mechanism: silver already deposited absorbs the light that would deposit more, so the shadows hold while the highlights catch up, and the process accommodates a range the paper's own contrast could not.

Sources:James M. Reilly, 1980§ Chapter One, Printing-out papers and their self-masking behaviour · Dusan C. Stulik and Art Kaplan, 2013§ Visual characteristics

Argued in:Salted paper, the image

Albumen

Longposition 3 of 3stated by the source

A long print-out scale with cleaner highlights and more apparent sharpness than a salted paper print from the same negative. The comparison is the atlas's own and is between two processes rather than between two prints, which is as far as the published literature can take it.

Sources:Dusan C. Stulik and Art Kaplan, 2013§ Visual characteristics · James M. Reilly, 1980§ Chapter 2, the role of organic binders

Argued in:Albumen, the image

Kallitype

Moderateposition 2 of 3stated by the source

Set in the developer, which is the kallitype's distinguishing property in this matrix: the same coating gives a sepia from a tartrate developer and a black from a borate one, and the ratio of the two stocks moves both the colour and the scale. A developed-out alternative process has a control a printed-out one does not.

Sources:Photographers' Formulary§ The three development formulas and the note on how the proportion of A to B moves the image colour

Argued in:Kallitype, the image

Van Dyke Brown

Longposition 3 of 3stated by the source

A long, self-masking print-out scale, as the salted paper. What the atlas records with it is that the colour is set by the size of the silver particles, so a longer exposure moves the scale and the hue together rather than separately.

Sources:Mike Ware§ The printing-out behaviour of the ferric-silver system

Argued in:Van Dyke Brown, the image

Palladiumfor platinum

Longposition 3 of 3stated by the source

Usually a little longer than platinum and lower in contrast from the same negative, which is Ware's comparison rather than the course's. A print-out platino-palladiotype is self-masking and this developed-out one is not, so the length here is a property of the metal and the developer rather than of the exposure.

Sources:Mike Ware, 2017§ 11.8 stoichiometry; Willis's palladiotype developer and clearing baths · Photographic Materials Group of the American Institute for Conservation; contributors Amy Brost, Luisa Casella, Saori Kawasumi Lewis and Stephanie Watkins, 2012§ Process overview; identification characteristics

Argued in:Palladium, the image

Image colour

The question What colour is the untoned print, and what moves it?

The scale: Image colour, a set of alternatives with no ordering

The colour of the untoned print, and what moves it. Colour in these processes is a property of particle size and of the image substance, not a dye.

1. Prussian blueThe image substance is Prussian blue and the colour is not adjustable without changing the chemistry.
2. Warm brownFinely divided silver or a warm metal; the hue follows particle size.
3. Purple-brownThe printed-out silver of a gold-toned printing-out paper.
4. Neutral to warmSet by the emulsion, the developer and the toner rather than by the process.
5. Set in the developerThe same coating gives different colours according to which developer it is put in.

Where a cell is empty The colour of the image substance has not been established.

Silver gelatinfibre base

Neutral to warmstated by the source

Neutral to warm according to the emulsion, the developer and the rate of silver deposition, and shifted deliberately by toning. It is the only process here whose colour is a manufacturing choice as well as a chemical one, which is why the toner matrix exists alongside this one.

Sources:Dusan C. Stulik and Art Kaplan, 2013§ The three-layer structure; the image within the emulsion layer · HARMAN technology Limited (ILFORD Photo), 2018§ The warm-tone emulsion and its image colour

Argued in:Silver gelatin, the image

Cyanotypeclassic

Prussian bluestated by the source

Prussian blue, deepening for some hours after washing as Prussian white re-oxidises in air. The colour is the image substance, so it is not adjustable without changing the chemistry - which is what the toned cyanotype does, by destroying the blue and replacing it.

Sources:Mike Ware, 2020§ 3.1 Chemistry of Prussian blue; 7.1 Classic cyanotype, wet processing · Dusan C. Stulik and Art Kaplan, 2013§ Process description; Main application of the cyanotype process

Argued in:Cyanotype, the image

Salted paper

Purple-brownstated by the source

Light brown to reddish brown untoned, and purplish and colder as gold toning takes hold - which became usual after 1847. The purple-brown of a museum salt print is a toned print, and the untoned colour is not what most people have seen.

Sources:Dusan C. Stulik and Art Kaplan, 2013§ Visual characteristics; Historical background · James M. Reilly, 1980§ Chapter One, gold toning and its effect on colour

Argued in:Salted paper, the image

Albumen

Purple-brownstated by the source

Rich purplish brown when gold toned. Untoned it is reddish, and Reilly calls the result of a plain acid gold bath flat, lifeless and reddish - which is a statement about the bath rather than about the process, and the reason the toner matters as much as the coating.

Sources:Dusan C. Stulik and Art Kaplan, 2013§ Visual characteristics · James M. Reilly, 1980§ Chapter Eight, Toning, Gold Toner Formulae

Argued in:Albumen, the image

Kallitype

Set in the developerstated by the source

Sepia from a tartrate developer and black from a borate one, from the same coating, with the ratio of the two stocks moving it between them. No other process in this matrix offers the colour as a tray decision after the exposure.

Sources:Photographers' Formulary§ The three development formulas and the note on how the proportion of A to B moves the image colour

Argued in:Kallitype, the image

Van Dyke Brown

Warm brownstated by the source

Warm brown, set by the size of the silver particles and shifted colder by gold or palladium toning. The name is the colour, and the particle-size explanation is the same one that makes a sulfide-toned print's hue depend on the image it came from.

Sources:Mike Ware§ The image substance and its colour · Bostick & Sullivan, Inc.§ Gold toning for POP, Vandyke, kallitype, albumen and salt prints

Argued in:Van Dyke Brown, the image

Palladiumfor platinum

Warm brownstated by the source

Warmer and browner than platinum, and very smooth. The smoothness is part of the colour statement rather than separate from it: finely divided palladium in the fibres gives a gradation with no grain structure to break it up.

Sources:Photographic Materials Group of the American Institute for Conservation; contributors Amy Brost, Luisa Casella, Saori Kawasumi Lewis and Stephanie Watkins, 2012§ Identification characteristics · Mike Ware, 2017§ Anderson on American practice; the palladiotype's image colour

Argued in:Palladium, the image

Surface

The question Where does the image substance sit relative to the paper?

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

Where the image sits relative to the paper, which is what a viewer actually sees first and what a conservator identifies the process by.

1. In the fibres, matteThe image substance lies among the paper fibres with no binder over it.
2. In a binder, glossyThe image sits in a coating on the paper rather than in it.
3. Emulsion over barytaA manufactured three-layer paper: emulsion, opaque baryta layer, paper core.

Where a cell is empty The physical structure of the print has not been established.

Silver gelatinfibre base

Emulsion over barytastated by the source

Emulsion over an opaque baryta layer over a bare paper core, with a hardened gelatin supercoat, and gloss or matte according to the finish. The baryta is what makes the whites white, and its microplatelets under magnification are how a conservator identifies the print.

Sources:Dusan C. Stulik and Art Kaplan, 2013§ The development of the baryta layer and its introduction in 1866; the three-layer structure and the microplatelets of the baryta layer under magnification · American Institute for Conservation, Photographic Materials Group§ Identification characteristics

Argued in:Silver gelatin, the image

Cyanotypeclassic

In the fibres, mattestated by the source

Pigment precipitated among the paper fibres, with no binder and no gloss. The paper is visible through the image because the image is inside it, which is what the process shares with every other alternative process in this matrix except the albumen.

Sources:Dusan C. Stulik and Art Kaplan, 2013§ Process description · Mike Ware, 2020§ 3.7 Chemistry of blueprinting

Argued in:Cyanotype, the image

Salted paper

In the fibres, mattestated by the source

Matte and sunken in, with the fibre visible, because the image silver is in the paper rather than on it. It is the plainest statement of the difference between a salted paper print and an albumen one, and it is what a viewer sees first.

Sources:Dusan C. Stulik and Art Kaplan, 2013§ Visual characteristics

Argued in:Salted paper, the image

Albumen

In a binder, glossystated by the source

Glossy, because the image sits in a protein layer on the paper rather than in it - and early prints are less glossy than the later double-coated and burnished ones, so the gloss dates the print as well as identifying the process.

Sources:Dusan C. Stulik and Art Kaplan, 2013§ Visual characteristics; the gloss and its reception · American Institute for Conservation, Photographic Materials Group§ Identification characteristics

Argued in:Albumen, the image

Kallitype

In the fibres, mattestated by the source

Silver among the paper fibres with no binder over it: matte. The kallitype and the Van Dyke are indistinguishable on this axis, which is why the columns that separate them are the exposure route and the developer.

Sources:Mike Ware§ The siderotype family and the absence of a binder

Argued in:Kallitype, the image

Van Dyke Brown

In the fibres, mattestated by the source

Colloidal silver among the paper fibres with no binder over it: matte, and the paper's own texture is part of the print. The particle size that sets the colour is also what sets how the surface reads at a distance.

Sources:Mike Ware§ The image substance and the absence of a binder

Argued in:Van Dyke Brown, the image

Palladiumfor platinum

In the fibres, mattestated by the source

Finely divided palladium among the paper fibres with no binder over it: matte, and smoother than the silver siderotypes because the metal is deposited more finely. The paper is more of the finished object here than in any other process in the matrix.

Sources:Photographic Materials Group of the American Institute for Conservation; contributors Amy Brost, Luisa Casella, Saori Kawasumi Lewis and Stephanie Watkins, 2012§ Identification characteristics · Dusan C. Stulik and Art Kaplan, 2013§ Process description

Argued in:Palladium, the image

What decides permanence

The question What is the characteristic way a print by this process fails, and is it under the printer's control?

This column is deliberately not a ranking. Which process lasts longest is a question about two particular prints and their storage; which failure to expect is a question about the process, and it is the one that changes what a printer does.

The scale: What decides permanence, a set of alternatives with no ordering

Not a ranking. A print fails for one characteristic reason, and knowing which one is worth more than a score, because it says what the printer can and cannot do about it.

1. Processing decides itFixing, washing and toning decide the outcome, and they are under the printer's control.
2. The metal decides itThe image substance is chemically inert; the enemies are handling, humidity and the paper.
3. The binder decides itThe image material outlasts what carries it; the binder or the paper is what fails.
4. Ordinary conditions attack itA common household condition destroys or reverses the image, and the cell names it.

Where a cell is empty The characteristic failure of the process has not been established.

Silver gelatinfibre base

Processing decides itstated by the source

The most controllable permanence in this matrix, and the controls are fixing, washing and toning rather than anything in the paper. That is a strength and a warning in one: a badly fixed fibre print is among the least permanent objects here, and nothing about the process protects it from its printer.

Sources:HARMAN technology Limited (ILFORD Photo), 2010§ Capacity without replenishment; silver concentration limits for print stability · HARMAN technology Limited (ILFORD Photo), 2017§ The fibre-base optimum-permanence wash sequence · Eastman Kodak Company, 2006§ Why tone a print - toning converts the silver image to an inert compound

Argued in:Silver gelatin, permanence

Cyanotypeclassic

Ordinary conditions attack itstated by the source

No silver and no fixer, and the pigment is highly insoluble - but alkali destroys it irreversibly, and a great many household things are alkaline, including most washing detergents and many modern papers' buffering. Light fading is the reversible half: a faded print recovers in the dark.

Sources:Mike Ware, 2020§ 9.2 Bleaching of cyanotypes by alkali; 9.3 peptization of Prussian blue · Mike Ware§ Papermaking: additives cause degradation

Argued in:Cyanotype, permanence

Salted paper

Processing decides itstated by the source

It turns almost entirely on the fixing and the washing rather than on the process, and the evidence is historical: Hill and Adamson's prints and the faded plates of The Pencil of Nature are the same chemistry used two ways. A process whose failures are all in the tray is one a careful printer can do something about.

Sources:Mike Ware, 2019§ 7.5 Fixation: chemistry and etymology; 17.3 Deterioration by environment · Dusan C. Stulik and Art Kaplan, 2013§ Historical background

Argued in:Salted paper, permanence

Albumen

Ordinary conditions attack itstated by the source

The characteristic failure is yellow highlight staining from silver sulfide, and it cannot be removed without destroying the print. The Fading Committee of 1855 was convened about it, which makes this the one process in the matrix whose permanence problem has its own institutional history.

Sources:American Institute for Conservation, Photographic Materials Group§ Deterioration and the Fading Committee of 1855 · James M. Reilly, 1980§ Chapter 9, fixation and washing

Argued in:Albumen, permanence

Kallitype

Processing decides itstated by the source

Its reputation for impermanence rests on clearing and toning rather than on the chemistry, and every one of its failures happens after the exposure. Residual iron is what stains and what catalyses, and a cleared and toned kallitype is a different object from an uncleared one.

Sources:Mike Ware§ Residual iron and the clearing of siderotypes · Photographers' Formulary, Inc.§ Clearing and the citrate developer

Argued in:Kallitype, permanence

Van Dyke Brown

Processing decides itstated by the source

As the kallitype: a poor reputation that belongs mostly to short clearing and washing rather than to the chemistry, which is the same argument the course makes about the salt print. Ware adds an objection of his own about the nitrate anion attacking the image, and the course records it as his rather than settling it.

Sources:Mike Ware§ The objection to the nitrate anion in the Van Dyke sensitiser · Mike Ware, 2019§ 5.10 Siderotype processes; 7.5 Fixation

Argued in:Van Dyke Brown, permanence

Palladiumfor platinum

The metal decides itstated by the source

A noble metal in the paper fibres, with the same argument as platinum and the same everyday enemy: relative humidity. When the image substance is inert, what fails is the paper it sits in and the conditions it is kept in, which moves the whole permanence question from the darkroom to the storage box.

Sources:Photographic Materials Group of the American Institute for Conservation; contributors Amy Brost, Luisa Casella, Saori Kawasumi Lewis and Stephanie Watkins, 2012§ Deterioration · Mike Ware, 2017§ The stability of platinum and palladium images and the role of relative humidity

Argued in:Palladium, permanence

Difficulty

The question How many things have to go right, on the atlas's own four-point band?

The scale: Difficulty, ordered

The difficulty band the process atlas records for each process, on the same four-point scale the atlas uses everywhere. It is about the number of things that must go right rather than about the hazard, which has its own column.

1. 1LowFew steps, wide latitude, and a first attempt that usually gives a print.
2. 2ModerateSeveral steps that each have to be right, and a coating or an exposure that rewards practice.
3. 3HighHand coating, a narrow window somewhere in the sequence, or a result that depends on conditions the printer has to control.
4. 4SpecialistBeyond a domestic darkroom as the course defines one, and usually a Level D process the course studies rather than performs.

Where a cell is empty The atlas records no difficulty band for the process.

Silver gelatinfibre base

Moderateposition 2 of 4stated by the source

The atlas's band. There is no coating step and the paper is manufactured to a specification, so what has to go right is the exposure, the development to completion, the fixing and the wash - four things, each of which has a published procedure.

Sources:HARMAN technology Limited (ILFORD Photo)§ Making your first black and white print

Argued in:Silver gelatin, where the course teaches it

Cyanotypeclassic

Lowposition 1 of 4stated by the source

The lowest band in the atlas and the reason the cyanotype is the course's Level A assignment in Part I. Two solutions, a coating, sunlight and a water wash: there is no developer, no fixer and no darkroom, and the failure modes are visible while they happen.

Sources:Mike Ware, 2022§ Introducing three varieties of cyanotype; preparation of sensitizers and instructions for their use · Bostick & Sullivan§ Cyanotype kit instructions

Argued in:Cyanotype, where the course teaches it

Salted paper

Moderateposition 2 of 4stated by the source

Salting, sensitising, printing out by inspection, toning, fixing and washing. Each step is simple and there are six of them, and the sensitised paper does not keep - which is the constraint that makes the process a session rather than a sequence of evenings.

Sources:James M. Reilly, 1980§ Chapter One; Chapter 5, sensitization; Chapter 9, fixation and washing

Argued in:Salted paper, where the course teaches it

Albumen

Highposition 3 of 4stated by the source

The salted paper's six steps with a coating step in front of them that is a craft in itself: the albumen is beaten, rested, filtered, floated and dried, and the three denaturing treatments Reilly describes each change the result. The gloss the process exists for is what the coating has to earn.

Sources:James M. Reilly, 1980§ Chapter 3, preparing and coating albumen; the three denaturing treatments · Dusan C. Stulik and Art Kaplan, 2013§ Process description

Argued in:Albumen, where the course teaches it

Kallitype

Highposition 3 of 4stated by the source

A hand-coated sensitiser, a developer whose composition sets the colour, a clearing sequence that the print's permanence depends on, and a toning step if it is to be kept. More things have to go right than in any other silver process here, and most of them after the exposure.

Sources:Photographers' Formulary§ Kit contents; the three development formulas and their times and temperatures · Photographers' Formulary, Inc.§ The citrate developer and its replenishment

Argued in:Kallitype, where the course teaches it

Van Dyke Brown

Moderateposition 2 of 4stated by the source

The kallitype without the developer: coat, print out by inspection, clear, fix and wash. Removing the tray in which the image is made removes the step with the most variables in it, which is why the two processes sit in different bands despite sharing a chemistry.

Sources:Photographers' Formulary, with safety data sheets from Columbus Chemical Industries and other suppliers§ Mixing the solutions - the sensitizer; the printing and processing sequence · Mike Ware§ Chemicals needed for the sensitizer

Argued in:Van Dyke Brown, where the course teaches it

Palladiumfor platinum

Highposition 3 of 4stated by the source

Hand coating with a two-part sensitiser whose ratio sets the contrast, a developer, a multi-stage clearing bath of EDTA and bisulfite, and a humidity that has to be controlled because the coating's behaviour depends on it. The metal is expensive enough that each of those has to be right the first time.

Sources:Mike Ware, 2014§ Making up the processing solutions - disodium EDTA at about 5 per cent w/v and its capacity · Bostick & Sullivan, Inc.§ Kit contents and wet processing - the EDTA and sodium bisulfite clearing bath

Argued in:Palladium, where the course teaches it

Safety classification

The question What is the course's hazard-assessed level for the process, and what 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 process has not been classified. Every process in the atlas carries a level, so an empty cell here would be a fault rather than a finding about the evidence.

Silver gelatinfibre base

Level Aposition 1 of 4stated by the source

The lowest classification in the matrix. Everything is bought as a made-up liquid concentrate and diluted - developer, stop bath and fixer - so nothing is weighed, no dust is raised and no concentrated acid is measured. The waste is the part that needs care rather than the process.

Sources:HARMAN technology Limited (ILFORD Photo)§ What ventilation do I need in my darkroom · HARMAN technology Limited (ILFORD Photo), 2010§ Dilution and handling

Argued in:Silver gelatin, hazards

Cyanotypeclassic

Level Bposition 2 of 4stated by the source

Potassium ferricyanide sets the level, and the control is a single absolute rule rather than a list: it must never meet a strong acid, because that liberates hydrogen cyanide. The compound itself is stable and low in toxicity, which is why the process can be a Level B assignment at all.

Sources:National Center for Biotechnology Information§ GHS classification; physical description · 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, 2002§ Chemical dangers, the reaction with acids

Argued in:Cyanotype, hazards

Salted paper

Level Bposition 2 of 4stated by the source

Silver nitrate sets it: a corrosive oxidiser that stains skin and everything else, handled as a solution and weighed as a solid. The sensitising step is the one that carries the control, and the printing and washing that follow it do not.

Sources:National Center for Biotechnology Information§ GHS classification; molecular weight; CAS

Argued in:Salted paper, hazards

Albumen

Level Bposition 2 of 4stated by the source

The same silver nitrate, plus isopropyl alcohol in the coating work and ammonium chloride in the salting. None of the three raises the level above B on its own; what the combination adds is a flammable liquid in a room that also holds an oxidiser, and they are kept apart.

Sources:National Center for Biotechnology Information§ GHS classification · National Center for Biotechnology Information§ Physical description; GHS classification · National Center for Biotechnology Information§ Physical description; GHS classification

Argued in:Albumen, hazards

Kallitype

Level Bposition 2 of 4stated by the source

Silver nitrate and ferric oxalate, both handled as solutions after one weighing. The oxalate is the reason the clearing baths matter for the printer as well as for the print, and the level is set by the sensitiser rather than by the developer.

Sources:National Center for Biotechnology Information§ Physical description; CAS; GHS classification · National Center for Biotechnology Information§ GHS classification

Argued in:Kallitype, hazards

Van Dyke Brown

Level Bposition 2 of 4stated by the source

Silver nitrate, ferric ammonium citrate and tartaric acid. The kit's own safety data sheet is the source the course uses, and it is a Tier 2 document rather than a manufacturer's technical sheet, which the page records with the classification.

Sources:Photographers' Formulary, with safety data sheets from Columbus Chemical Industries and other suppliers§ Chemicals contained in this kit · National Center for Biotechnology Information§ GHS classification

Argued in:Van Dyke Brown, hazards

Palladiumfor platinum

Level Bposition 2 of 4stated by the source

Sodium tetrachloropalladate and ferric oxalate in the sensitiser, and potassium chlorate as the contrast agent - which is the substance that has to be handled with the most care here, being a strong oxidiser that must be kept from anything combustible. The course teaches palladium and not platinum, and that ruling is about the metal's cost and handling rather than about this list.

Sources:National Center for Biotechnology Information§ Physical description; CAS; GHS classification · Photographers' Formulary, Inc.§ The potassium chlorate contrast agent and its mechanism

Argued in:Palladium, hazards · Why the course studies platinum and prints palladium

Cost

The question What band does the atlas record, and does the price file hold a figure for the material that dominates the cost?

Every scored cell in this column names the priced item the band rests on. Where the file is silent the cell is empty, which is why the most expensive process in the matrix is the one with no score.

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 figure for the material that dominates this process's cost, so the band the atlas records cannot be shown its arithmetic here. The band stays on the process page as the course's estimate; this column declines to certify it.

Silver gelatinfibre base

££position 2 of 4an inference by this course

The whole chain is priced, including at last the paper the process is named for. Paper developer is 10.52 to 20.03 for 500 mL to 1 L of concentrate at 1+9, stop bath 10.66 to 12.18, rapid fixer 21.05 to 25.98, a washing aid 12.83 to 17.99, and fibre-base 8 by 10 paper 47.04 to 150.28 for 25 to 100 sheets, which is 1.50 to 1.88 a sheet against 0.96 to 1.34 for the resin-coated equivalent. The band stays where the atlas put it and the cell no longer rests on a substitute: fibre costs about half as much again as RC at the same size, and the chemistry either process consumes is the same.

Sources:The course price file, GBP, checked 2026-09-07§ paper-developer (500 ml to 1 L of concentrate, diluted 1+9); stop-bath (500 ml of citric acid concentrate, diluted 1+19); rapid-fixer (1 L of ammonium thiosulfate concentrate, diluted 1+4 for film); rc-paper-8x10 (25 to 100 sheets, 8 x 10 in, variable contrast RC) · The course price file, GBP, checked 2026-09-07§ fb-paper-8x10 (25 to 100 sheets, 8 x 10 in, variable-contrast fibre-base, glossy); washing-aid (1 L of liquid concentrate, or a powder making 3.8 L)Both added to the price file on 7 September 2026. Fibre-base paper was the substitution this cell previously had to make.

Argued in:The laboratory planner and its price file

Cyanotypeclassic

£position 1 of 4stated by the source

The cheapest process in the matrix, and now the only one that can be costed both ways. Ready-coated paper is 18.95 to 36.95 for 20 to 50 sheets at 8 by 10; the two raw salts a coater buys instead are 17.99 for 230 g of ferric ammonium citrate and the same for 230 g of potassium ferricyanide, so a pair of jars costs about what a box of coated paper costs and makes very much more sensitiser than a box holds. There is no developer, no fixer and no silver anywhere in the process, and the wash is water.

Sources:The course price file, GBP, checked 2026-09-07§ cyanotype-paper (20 to 50 pre-coated sheets, 8 x 10 in) · The course price file, GBP, checked 2026-09-07§ ferric-ammonium-citrate (230 g); potassium-ferricyanide (230 g)Both added to the price file on 7 September 2026. Neither listing states which grade of the iron salt it is, and the cyanotype literature specifies the green.

Argued in:The laboratory planner and its price file

Salted paper

££position 2 of 4an inference by this course

Silver nitrate dominates and the file prices it: 59.95 to 112.90 a jar, being 25 g at the lower figure and 10 g at the higher. The fixing bath can now be costed too, at 14.70 the kilogram for the raw thiosulfate. What is still missing is at both ends of the process - kaolin for decolorising the silver bath, and gold chloride for the toning this course argues the print's permanence depends on - and both are now named gaps rather than silences. The band is the atlas's; what this cell adds is which single purchase decides it and which one it cannot see.

Sources:The course price file, GBP, checked 2026-09-07§ silver-nitrate (one jar: 25 g at the lower figure, 10 g at the higher) · The course price file, GBP, checked 2026-09-07§ sodium-thiosulfate (1 kg, pentahydrate)Added to the price file on 7 September 2026, and closing the gap this cell recorded when it was written. Gold chloride and kaolin remain unpriced and are named in the file's gaps.

Argued in:The laboratory planner and its price file

Albumen

££position 2 of 4an inference by this course

The salted paper's silver nitrate, at the same priced 59.95 to 112.90 a jar, and then a coating bench nothing in the price file reaches: about 35 large eggs to the litre of albumen, ammonium chloride in it, glacial acetic acid in it, isopropyl alcohol by the tray for the double-coating route, and a thinner and smoother paper than the salted print needs. Every one of those is now a named gap, which turns the empty half of this cell from an omission into a list. The coating adds labour rather than cost, which is why the difficulty column separates this process from the salted paper and this one does not.

Sources:The course price file, GBP, checked 2026-09-07§ silver-nitrate (one jar: 25 g at the lower figure, 10 g at the higher)Eggs, ammonium chloride, glacial acetic acid, isopropyl alcohol and thin smooth all-rag paper are all named in the price file's gaps as of 7 September 2026, and none is priced.

Argued in:The laboratory planner and its price file

Kallitype

Not established

Silver nitrate is priced at 59.95 to 112.90 a jar and the iron chemistry is not: ferric oxalate, which is the largest per-print cost after the silver, and the tartrate, and the clearing bath. All of them are now named in the price file's gaps, where when this cell was written none of them was, so the absence is recorded rather than merely true. The obstacle for the ferric oxalate is not that nobody sells it: three suppliers publish three different strengths under the same name, and a price with no strength beside it cannot become a cost per coated sheet. What can still be said is the order - the silver dominates a kallitype's cost and the iron does not.

Sources:The course price file, GBP, checked 2026-09-07§ silver-nitrate (one jar: 25 g at the lower figure, 10 g at the higher)Ferric oxalate, Rochelle salt and the clearing-bath solids are named in the price file's gaps as of 7 September 2026, and none is priced.

Argued in:The laboratory planner and its price file

Van Dyke Brown

Not established

Half the sensitiser can now be costed and the process still cannot. Silver nitrate is 59.95 to 112.90 a jar and ferric ammonium citrate 17.99 for 230 g, which between them are most of what a Van Dyke consumes; tartaric acid is unpriced and named as a gap, and so is the sodium thiosulfate route's alternative in the clearing bath. The Van Dyke is usually described as the cheapest silver alternative process, and this matrix still cannot confirm that from the course's own shopping data - though it is now much closer to being able to than the kallitype beside it.

Sources:The course price file, GBP, checked 2026-09-07§ silver-nitrate (one jar: 25 g at the lower figure, 10 g at the higher) · The course price file, GBP, checked 2026-09-07§ ferric-ammonium-citrate (230 g); sodium-thiosulfate (1 kg, pentahydrate)Both added to the price file on 7 September 2026. Tartaric acid is named in that file's gaps and is not priced.

Argued in:The laboratory planner and its price file

Palladiumfor platinum

Not established

The price file holds no palladium salt, and palladium is the entire cost of a palladium print. What has changed since this cell was written is that the absence is now argued in the file itself: palladium and platinum salts are a named gap, with the two traps a buyer meets written into it - a supplier prices the salt and not the metal, and a made-up solution is priced by volume, so a listing without a strength on it settles nothing. The atlas records the band as three pounds signs on the course's own relative scale, and this column has no figure to support it, which makes the most expensive process in the matrix the one with no score and says something true about the course's shopping data rather than about the process.

Sources:The course price file, GBP, checked 2026-09-07§ silver-nitrate (one jar: 25 g at the lower figure, 10 g at the higher)Cited only to show what the file does hold for a comparable sensitiser salt. Palladium and platinum salts, and ferric oxalate, are named in the file's gaps as of 7 September 2026 and none is priced.

Argued in:The laboratory planner and its price file