Mottled development

Owned by Uneven Development, Bromide Drag and Surge Marks, which adds the measurement point this fault needs most: mottle is invisible on a step wedge, because a patchiness of a few millimetres inside a large even area has nowhere to show itself on a series of small uniform patches, so a process can be certified in control and still make mottled skies. That page also carries the 1928 primer’s second route to it, in the fixing bath rather than the developer. This entry was assembled from diffusion, swelling and the journey into the emulsion and the agitation arm of the solvent series.

What you see

Areas of non-uniform density with no direction to them — a general blotchiness, soft-edged, unrelated to the picture and unrelated to the geometry of the film.

The absence of a direction is what places it. A fault with an axis is flow that organised itself; a fault without one is flow that never happened.

Likely causes

1. Inadequate agitation.
2. A reduced-agitation or semi-stand regime pushed past what the material and the dilution will carry.
3. Too little solution for the surface being developed, so that depletion is a property of the tank rather than of the boundary layer.

What is happening: the chemistry and physics

The developer immediately against the emulsion is being consumed as it works, and it has to be replaced. With enough agitation the unstirred boundary layer is kept thin and the supply keeps up. With too little, the layer thickens and local depletion survives — highlights exhaust their own neighbourhoods and slow down, shadows sit in solution that is barely used and keep going.

Where that depletion is allowed to organise itself into a flow it produces bromide drag, which has a direction. Where it is neither refreshed nor allowed to settle into a flow it produces mottle, which does not.

Kodak’s troubleshooting table records both ends of the range as separate failures — streaks of non-uniform density against excessive or uneven agitation, mottle against inadequate agitation - and neither is cured by changing the developer.

Diagnostic questions

• Does the fault have a direction? No direction is mottle. Downward streaks from dense areas are bromide drag. Marks at the perforation pitch are surge marks.
• Was the agitation reduced deliberately? A semi-stand cell in an experiment is expected to show this, and it is a result rather than a fault.
• What was the solution volume against the film area? A tank run at less than its rated volume is running a depletion experiment nobody designed.
• Is it on every frame, or on part of the roll? All frames points at the regime; part of the roll points at the loading.
• Is the same blotchiness present in the rebate? If so, look at fog instead, because the rebate saw no exposure and cannot show a development pattern that depends on one.

Corrective action

None on the negative.

For the next film, restore a published agitation script and change nothing else. If reduced agitation is the intention, dilute further or shorten rather than agitating still less, and expect to trade uniformity for compensation — the two are the same physics.

Prevention

Agitate to a written script, at a stated interval, and record it.

Fill the tank to its rated volume.

Where you are experimenting with agitation, hold the time and the dilution still and change only the agitation, so that mottle when it appears is attributable. That is how the developer laboratory’s own agitation arm is designed, and it is the reason its semi-stand cell is described as a result rather than as a failure.