Print mottle

Owned by print faults and poor maximum black. Its mechanism belongs to uneven development, bromide drag and surge marks, and uneven print development covers the directional and whole-sheet cases; this entry is the soft patchiness inside a tone.

What you see

A soft, irregular patchiness inside an area that should be one tone — a sky, a wall, an out-of-focus background, a plain studio backdrop. No direction, no edge, no period. Kodak’s own description in the Z-133 table is exactly this: “Mottle — areas of non-uniform density”.

It is worst on large prints and in large areas of even middle tone, and it is more visible on a smooth surface than on a textured one.

And it is invisible on a test strip, which is the practical difficulty and the reason this entry exists separately from the other print faults. A test strip is a row of small patches with hard boundaries; a patchiness of a few millimetres inside a tone has nowhere to appear on one.

Likely causes

1. Too little developer in the dish.
2. Agitation too gentle, or too regular.
3. A developer near the end of its capacity.
4. A print not fully or promptly covered.
5. A dish too small for the paper, so the sheet cannot lie flat and be swept evenly.

What is happening: the chemistry and physics

Developer is consumed and its by-products released fastest where most silver is being reduced. In a dish that means under the darker parts of the print, and the thin layer of solution immediately against the emulsion there becomes depleted while the solution over the light areas stays fresh.

Kodak’s statement of the purpose of agitation describes exactly what is failing: it exists “to maintain uniform solution activity by removing exhausted solution from the emulsion surface and replacing it with fresh”, and it “must be uniform throughout”.

Mottle is the under-agitated end of that lever. The Z-133 table lists it against inadequate developer agitation, and — in the row above — lists streaks of non-uniform density against excessive or uneven agitation. Two faults, one control, opposite directions.

🧮Why a big dark print is the hard case

ILFORD publish the capacity of one litre of MULTIGRADE developer at 1+9 as 50 sheets of 8 × 10 inch fibre paper, or 100 of RC.

One 16 × 20 inch print is four 8 × 10s by area, so a litre holds about twelve of them on fibre. And that figure is an average across whole sheets, while the developer under a large area of deep black is doing a great deal more than the average.

The failure is therefore local before it is general: the bath still develops perfectly well, and one region of one print does not, because its own small reservoir ran down before the print was finished. That is why mottle appears in the dark areas of big prints while the small prints from the same tray look fine.

ILFORD add a second figure worth noting: their cool-tone paper achieves “approximately half these capacities”, because it needs longer development times.

And more time will not fix it. ILFORD state that development can be extended to six minutes without noticeable change in contrast or fog, so a paper developer is worked to completion by design; extending the time does not compensate for a region that is not receiving fresh developer.

Diagnostic questions

• Is the patchiness inside an even tone, with no direction or edge? That is mottle. A directional gradient is uneven print development; a hard-edged mark is something else entirely.
• How deep was the solution? ILFORD ask for enough to fill the dish “to a depth of about half full”, and most cases in a home darkroom are a centimetre of developer in a large tray.
• How was it agitated? ILFORD recommend continuous agitation in dishes and trays, by rocking. Gentle intermittent rocking is a tank scheme applied in the wrong vessel.
• Did the rocking change direction? A steady rhythm sweeps the same regions every time.
• How many prints had been through, and how dark were they? Against the capacity table, not the clock.
• Is it only the large prints? Then it is the local reservoir, and the answer is volume rather than a fresh bath.
• Did the print go in flat? A sheet dropped flat traps solution unevenly; edge-first sweeps across.
• Is it visible on a test strip? It will not be. That is not evidence of absence.

Corrective action

None on the print. The silver was never developed.

Make it again with more solution and a changed rocking pattern. If you are unsure which of the two was the cause, change the volume first, because it is the cheaper test and the commoner fault.

Prevention

Use enough solution and a dish comfortably larger than the paper. Half the dish’s depth, per ILFORD’s own instruction.

Agitate continuously and irregularly. ILFORD ask for continuous rocking in dishes; the useful addition, which the sheets imply rather than state, is to lift a different edge each time so that the flow pattern does not repeat.

Slide the print in from one edge and push it under at once.

Keep a running total against the published capacity, remembering that dark prints spend more than the average and that a cool-tone paper halves the figure.

And test for it on a real print rather than on a strip. A sheet given an even exposure with no negative in the carrier, developed normally, will show mottle if your session produces it — and nothing else in your routine will.