Uneven print development

Owned by uneven development, bromide drag and surge marks, rather than by the print page, because the mechanism is identical to the film case: it is local exhaustion in a dish instead of a tank.

What you see

A print whose tone changes across the sheet in a way the negative does not account for. Three shapes recur and they point at different things:

• A soft patchiness in an even tone — a sky, a wall, an out-of-focus background — with no direction and no edge. That is the paper version of mottle, and it is the under-agitated end.
• A directional gradient, one edge or one corner lighter than the rest, often the edge that was furthest from where you rocked.
• A drift from the centre of a large print outwards, on a print with a big dark area in the middle.

It is worst on large sheets and on prints with large continuous areas, and it is invisible on a test strip, because a test strip is a set of small patches with hard edges and has nowhere to show a difference within a tone.

Likely causes

1. Too little solution in the dish.
2. A rocking rhythm that never changes direction.
3. A developer near its capacity, particularly under a large area of deep black.
4. A temperature gradient across the dish.
5. The sheet not fully or not promptly covered.

What is happening: the chemistry and physics

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

Kodak’s Z-133 states what agitation is for in one sentence — removing exhausted solution from the emulsion surface and replacing it with fresh, uniformly throughout — and lists the two failure modes in the same table: mottle against inadequate agitation and streaks of non-uniform density against excessive or uneven agitation. Both ends of the lever fail, and they fail differently.

🧮What the capacity table says about a big print

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

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

The practical consequence is not that the developer stops working. It is that on a big dark print the local reservoir under the blacks can be exhausted long before the bath is, and what you see is unevenness rather than weakness.

Temperature enters through the same door. This course takes about 9 per cent of development time per degree Celsius near 20 °C from ILFORD’s compensation chart, so a two-degree difference between the side of a dish on a cold worktop and the side over the warm bench is close to a twenty per cent difference in effective development across the print.

Diagnostic questions

• How deep was the solution? ILFORD ask for enough to fill the dish “to a depth of about half full”, and most unevenness in a home darkroom is a centimetre of developer in a big tray.
• Did the rocking change direction? A steady front-to-back rhythm sweeps the same regions every time.
• How many prints had been through the bath, and how dark were they? Compare against the capacity table rather than against the clock.
• Is the patchiness in the even tones or at the edges? Even tones with no direction is under-agitation; a directional gradient is a flow pattern.
• Did the print go in flat? A sheet dropped flat traps solution and air unevenly; edge-first sweeps across.
• Was the dish on a cold surface, or half over the edge of the bench?
• Is it on the last prints of an evening only? Then it is capacity, and the running total names it.

Corrective action

Nothing on the print. Make it again with more solution and a changed rocking pattern.

Note that the development time is rarely the answer: ILFORD state that development can be extended to six minutes without noticeable change in contrast or fog, so a longer time will not even out a print whose problem is that some of it is not getting fresh developer.

Prevention

Use enough solution. A dish half full, per ILFORD’s own instruction, and a dish comfortably larger than the paper.

Rock irregularly. Lift a different edge each time. The aim is to break up the flow pattern, not to maintain one; regularity belongs in the timing, not in the direction.

Slide the sheet in from one edge and push it under at once, so the solution sweeps the surface rather than closing over it.

Keep a running total against the published capacity, and remember that dark prints spend more than the average.

Match the dish temperature to the developer, and keep the dish off a cold stone worktop and out of a draught.

And do not chase evenness with a short time. ILFORD’s compensation chart carries the warning in capitals that development times below five minutes are not recommended because of the risk of uneven development; on paper the equivalent is that the published minimum is a minimum, and the range above it is where evenness lives.