Silver gelatin developing-out print on resin-coated base

A resin-coated print carries the same emulsion as a fibre-base print and a completely different base, and almost every practical difference between the two is one sentence long: the paper core never gets wet. Read the fibre entry first for the chemistry; this one is about what the polyethylene changes.

The chemistry

The image chemistry is unchanged. Light makes a latent image in silver halide suspended in gelatin, and a developer amplifies it by reducing whole crystals to metallic silver. What changes is the support.

The structure, in the Getty’s own words. “The emulsion side of the paper is coated with PE filled with titanium dioxide (TiO₂). The bright-white pigmented layer simulates the visual effect of the baryta layer of fiber-based, baryta-coated photographic papers. The emulsion layer is coated onto the pigmented layer and overcoated by a topcoat or supercoat of hardened gelatin as protection against mechanical damage.” Two sheets of polyethylene sandwich the paper; the one under the emulsion carries the pigment.

Titanium dioxide is a substitute for baryta, not an addition to it. Two different insoluble white solids chosen for the same optical property, in two different binders: put an opaque brilliant white between the image and the fibres so that the highlights are the paper’s whiteness rather than the pulp’s.

⚗Telling the two supports apart is harder than it looks

The Getty’s analytical section records that in X-ray fluorescence “the main spectral peaks of Ti and barium (Ba) almost overlap perfectly”, and that distinguishing them needs the barium Kα and Kβ peaks at 32.19 and 36.38 keV and the other barium peaks below the Ba L peaks, which are missing in spectra of material containing only titanium.

That is a conservator’s problem rather than a printer’s, and it is here because it is the clearest demonstration that the two papers are the same idea executed in different materials. By eye the distinction is easy — a fibre print’s edge shows fibres and an RC print’s shows a plastic laminate — and by instrument it is not.

Historical workflow

Expose, develop, stop, fix, wash, dry, and every number in the second half is smaller.

Fixing. ILFORD’s rapid fixer gives resin-coated paper 30 seconds at working strength against one minute for fibre base, and a capacity without replenishment of 80 sheets of 20.3 × 25.4 cm per litre, or 4 m², against 40 sheets and 2 m² for fibre. Replenishment is 250 mL/m² against 500.

Washing. ILFORD gives a minimum of 30 seconds in vigorous fresh running water, or three trays of still water for 15 seconds each with agitation — and attaches a warning that has no counterpart on the fibre sheet: do not over-wash, because water ingress at the edge can swell and damage the print. Kodak’s Hypo Clearing Agent is not recommended for resin-coated papers, which already have a short wash time of four minutes.

Stop bath. ILFOSTOP’s published capacity is 60 resin-coated sheets per litre against 30 on fibre base. That factor of two, like the others, is a measurement of absorbency rather than of anything in the emulsion, and the stop-bath lesson draws it in section.

!The one place where more washing is worse

Everywhere else in this course, a longer wash is a safer wash. On a resin-coated print it is not, because the only route into the paper core is the cut edge, and prolonged soaking is how water gets there. That is a genuinely unusual instruction and it is worth remembering as the exception, along with its reason: the base is sealed, so there is very little to wash out and a real mechanism by which washing does harm.

The image

Indistinguishable from the fibre print at arm’s length, and different in the hand. The emulsion and its supercoat are essentially the same, so the tonal scale, the colour and the contrast controls are the fibre-base entry’s. What differs is the object: a laminated sheet that dries flat, does not need flattening, and has an edge that shows plastic rather than fibre.

Finishes are the manufacturer’s, and ILFORD’s own comparison of two generations of its resin-coated multigrade paper is the kind of document a printer should read before assuming that a paper’s behaviour has stayed constant across a name change.

Permanence

The permanence argument is different rather than simply worse, and the honest position is that the course can state the fixing and washing chemistry with confidence and cannot state a lifetime.

Almost nothing is retained in the base, because the base never wets. ILFORD’s silver ceiling for resin-coated paper is 4 to 6 g/L, against below 2 g/L for fibre-base prints of commercial permanence and below 0.5 g/L for maximum long-term stability — and the reason it can be higher is stated explicitly: the polythene protects the base on both sides, so nothing is retained in the paper core. Above the fibre-base level, compounds may remain in a fibre paper base after washing and over time possibly contribute to print staining. The resin-coated sheet has no such reservoir.

What the polyethylene does over decades is a separate question, and this course has not read a source that answers it. The image-layer failures are the fibre print’s — residual thiosulfate, residual silver, silver mirroring and microspots from oxidative attack — and IPI’s storage guidance and its priority apply unchanged: enclosures cannot overcome deficiencies in the storage climate, and improving the climate is more effective overall.

Toning behaves differently, and that is a real difference. A sulfide or selenium toner works on the image silver, which is in the same place on both papers; but the sequences the toning literature publishes are largely written for fibre base, and a paper that fixes in 30 seconds and washes in four minutes is not carrying the same chemistry into the toning tray. Part XX is where that should be settled, and this entry does not settle it.

Hazards

Level A, and marginally lower in practice than the fibre-base print for the same reason it is quicker: less liquid is carried between trays and less is discarded. Developer, stop and fixer at working dilution, nitrile gloves, eye protection, a well-ventilated room.

Spent fixer is silver-bearing and belongs to recovery. The higher silver ceiling means an RC printer’s bath reaches exhaustion later, which is a convenience and not a licence: ILFORD’s own note is that the paper figures may be exceeded whenever print stability is not critically important, which makes a capacity a decision rather than a physical limit.

Titanium dioxide appears in this atlas twice and the second appearance is the one a hand-coating printer must notice. Ware’s specification for a paper intended for the iron-based processes lists what the sheet must not contain, and “dyes or white pigments such as titanium dioxide” is on it. The pigment that makes a factory paper white is one of the things that makes a factory paper unusable for a cyanotype.

Where the course teaches it

Part XVIII owns the paper structure and the developer-paper pair, Part XIX the printing practice, and Part XX the toning. None is yet written.

What is written and applies today: Part XI, whose fixer capacity and exhaustion lesson carries every resin-coated figure quoted above, and Part XII, whose physics-of-washing lesson explains why the two papers need such different washes and whose permanence lesson covers what happens afterwards. The troubleshooting atlas carries the print faults with their confirming tests.

A final note for the reader deciding between the two papers, because the atlas should not duck it. The resin-coated sheet is faster, easier, flatter and cheaper in water and time; the fibre sheet has the longer published record and the surface most exhibition printing is done on. The course teaches both and states the trade rather than recommending one, which is the same position it takes on platinum against palladium and for a related reason: the honest comparison is between what each buys and what each costs, not between a real material and an inferior one.