Silver gelatin developing-out print on fibre base

A gelatin silver print on fibre base is the material most of the twentieth century’s photographs are made of, and the one this course’s whole printing and permanence apparatus is built around. What distinguishes it from its resin-coated sibling is not the emulsion, which is essentially the same, but what is underneath it: a bare paper core that soaks like blotting paper.

The chemistry

A developing-out paper, which is the whole difference from every printing-out process in this atlas. Light makes a latent image too small to see in silver halide crystals suspended in gelatin, and a developer then amplifies it by reducing whole crystals to metallic silver. Reilly’s figure for what that saves is the one to carry: printing out needs up to 100,000 times the light energy, which is why a print-out paper can only be contact printed and this one can be enlarged onto.

The structure is three functional layers and one absence. The AIC puts the identification difference plainly: the image “can either be partially within the paper structure as with printing-out processes, or on top of a baryta layer as with developing-out processes”. Putting an opaque white coat of barium sulfate in gelatin between the emulsion and the fibres does three things at once — it stops the emulsion sinking in, it hides the pulp’s colour and texture, and it gives the highlights a brightness the paper alone cannot reach. Over the emulsion sits a hardened gelatin supercoat against mechanical damage.

The absence is the base. There is no polyethylene, so the paper core wets, and everything below in this entry follows from that one fact.

Image colour is a rate rather than a recipe. Wall’s controlled series, quoted in full on Part V’s chlorobromide project, made emulsions from pure chloride through 5, 10 and 20 per cent bromide to pure bromide, developed every one in a single metol-hydroquinone developer, and found the same coloured image throughout — “which conclusively proved that the length of exposure with a constant developer has nothing to do with the color of the image… it is the rate of development, or in other words, the rate of deposition of the silver, which is the determining factor of the color of the image, and not the composition of the emulsion.” Halide ratio sets speed and the shape of the scale; the developer and the dilution set the colour.

Historical workflow

Expose under an enlarger or in a contact frame, develop, stop, fix, wash, dry — and the numbers that matter are all in the last three.

Fixing. ILFORD’s rapid fixer gives fibre-base paper 1 minute at working strength against 30 seconds for resin-coated, and its capacity without replenishment is 40 sheets of 20.3 × 25.4 cm on fibre base per litre against 80 on resin-coated, or 2 m² against 4 m². Replenishment is 500 mL/m² for fibre against 250 for resin-coated. Every one of those factors of two is the same absorbency difference measured a different way.

Washing. ILFORD’s optimum-permanence sequence for fibre base is one minute’s fixation, a five-minute first wash, ten minutes in WASHAID at 1+4, and a five-minute final wash. Kodak’s Hypo Clearing Agent reduces a wash to 10 minutes for single-weight papers and 20 for double-weight, against 20 to 30 minutes without it for film — and Kodak states that it is not recommended for resin-coated papers, which already have a short wash time of four minutes.

⚗Why a washing aid works, and why fibre needs one

ILFORD describes WASHAID as a hypo-eliminator formulated to aid the efficient removal of the thiosulphate by-products of fixation by ion exchange, particularly useful in speeding the washing of fibre-based papers and where a hardening fixer has been used.

The physics behind it is Part XII’s, and it is worth the sentence: fibre-based papers absorb processing solutions readily into the paper base, so the thiosulfate is not on the sheet but in it, and diffusing back out of a paper core is slow. A washing aid replaces thiosulfate with an ion that leaves more easily. The stop bath page measures the same absorbency from the other end: ILFOSTOP’s capacity is 60 resin-coated sheets per litre and 30 on fibre base, and the factor of two is a manufacturer’s measurement of an absorbency difference rather than anything to do with the emulsion.

The image

Surface is the paper’s, and the range is wide: gloss, semi-matte, matte, and the textured finishes, all above the same baryta layer. Under magnification the Getty records what that layer looks like — at a damaged edge, “separated microplatelets of the white (more white than the paper fibers) baryta layer” still held in the fibres, and in an intact area a layer that “looks flat, solid, and almost structureless”.

Colour runs from cold blue-blacks to warm browns, and the levers are the emulsion’s halide, the developer and its dilution, and toning afterwards. Part XVIII owns the paper-and-developer pairing and Part XX the toning.

Contrast is chosen rather than fixed, by paper grade or by variable-contrast filtration — a sheet carrying two emulsions of different contrast responding to different colours of printing light. That is Part XVIII’s third lesson and it has no counterpart anywhere else in this atlas: every alternative process here sets contrast in the sensitiser, in the developer or in the negative.

Dating a print by its support. The AIC gives 1894 for baryta layers added to commercial developing-out papers and 1900 for their introduction to Kodak papers, and the Getty’s timeline agrees. Baryta itself is older than the gelatin emulsion: the Getty dates its introduction by José Martinez-Sanchez and Jean Laurent to 1866.

Permanence

This is the process with the most controllable permanence in this atlas, and none of the controls is in the paper.

Residual thiosulfate is the first. Hypo left in the sheet converts image silver to silver sulfide over years, and a fibre base holds several times what a surface film does, then feeds it back into the emulsion in the next tray. That is what the washing aid and the long wash are for.

Residual silver is the second, and it is a fixer problem rather than a wash problem. ILFORD’s silver ceilings are the clearest statement in the corpus: below 2 g/L for fibre-base prints of commercial permanence, which is about forty 8 × 10 prints per litre, and below 0.5 g/L for maximum long-term stability, which is about ten. Above the fibre-base level, compounds may remain in the paper base after washing and over time possibly contribute to print staining. Note what the arithmetic does not say: the tighter standard does not remove more silver from the print, it retires the bath sooner so that the last bath a print meets is closer to fresh.

Oxidative attack is the third and it happens in storage rather than in the darkroom. IPI defines silver mirroring as oxidation in which the image silver migrates to the surface, creating a mirror-like appearance, and microspots as small red or orange spots from localised oxidation. Its framing guide gives the mechanism inside a frame: reactions caused by poor framing materials, like those from air pollution, are often oxidations that fade the image, and the faded silver can migrate to the surface and be converted back to metallic silver by other pollutants.

Toning is the countermeasure, and Kodak’s claim is that toning converts the image to an inert compound and that all its toners protect the image whether or not they produce a colour shift. Selenium, sulfide and gold have their own entries; iron-blue is the one that does not protect.

IPI’s own priority is worth ending on, because it outranks everything above: enclosures cannot overcome deficiencies in the storage climate, and improving the climate is more effective overall.

Hazards

Level A, and it is the level most of this course’s darkroom work runs at: a developer, a stop bath and a fixer at working dilution, in trays, at room temperature, with nitrile gloves, eye protection and a well-ventilated room. Nothing is heated above 50 °C and no volatile solvent is involved.

Two qualifications. Mixing from concentrates or from raw chemicals raises the level of that step, not of the session — the rubric permits a declared higher-level step with its controls stated, and the developing agents are the reason. And the spent fixer is silver-bearing and belongs to recovery rather than to a drain; Part XII owns that argument and the numbers behind it.

Where the course teaches it

Part XVIII, Printing Chemistry, owns the material: the structure of a printing paper, paper emulsions and image tone, variable-contrast papers, print developer chemistry and the developer-paper pair, a Level A lab on mixing and comparing print developers, an experiment on maximum black, base white and dry-down, and a break/fix page on the print that will not go black. Part XIX, Fine Printing, owns the practice, and Part XX the toning. None of the three is yet written.

What is written and load-bearing today is the second half of the process. Part XI owns fixing chemistry, capacity and exhaustion; Part XII owns the physics of washing, the archival processing sequence, permanence and image deterioration, and silver recovery. Every number in this entry’s permanence section comes from those written parts, and a reader who wants the argument rather than the summary should read them rather than this page.