Cinch and pressure marks

Owned by the emulsion under stress, which places them among the mechanical faults; their density half is discussed on the flow-marks page alongside the marks they are confused with.

What you see

Sharp crescents or half-moons, a few millimetres across, usually in groups, and of increased density on the negative — so they print as light marks.

They have no relation to the picture. They frequently appear in clusters along one part of a roll, or at the inner end of a film that was wound tight.

They are not grooves. Run a fingernail lightly across one, or look at it under raking light: there is nothing to feel and nothing to see as a topography. The material is undamaged; only its response to the developer has changed.

Likely causes

1. Cinching — pulling a loose roll tight by turning the spool, so that the whole coil slides against itself under tension. That is where the name comes from.
2. Forcing a film onto a spiral reel, particularly a damp one, where the film buckles rather than feeding.
3. Bending or kinking the film while loading in the dark.
4. Excessive transport tension, in a camera or a machine.

Kodak’s Z-133 gives three causes for Pressure marks — plus-density areas (e.g. half-moons, crescents, etc.): poor film handling, excessive tension, and camera malfunction. Their corrective actions are instructive about where the fault sits — train the operators, check the machine, and notify the customer. Two of the three are outside the darkroom.

What is happening: the chemistry and physics

Mechanical work on an emulsion before development makes the worked area more developable. Local pressure, bending or friction on a silver halide crystal produces developable centres in it, by the same route as a photon does in the end — a small speck of silver that catches the developer — but arrived at mechanically rather than photochemically.

The consequence is that the mark is a density change and not a physical injury. There is no groove, the gelatin is intact, and nothing has been removed. The film simply developed further where it was pressed.

That is why the direction of the density change is the whole diagnosis, and it runs the opposite way from the two faults it is confused with.

!Three faults, and the density tells you which

	Density on the negative	Prints as	Feel	Made when
Cinch or pressure mark	More	Light	Nothing	Before development
Contact mark	Less	Dark	Nothing	In the tank
Emulsion-side scratch	Less	Dark	A groove	After the layer was wet

A darker mark and a lighter mark, on the same film, from causes at opposite ends of the process. Reading the direction first eliminates two of the three before you look at anything else.

A second consequence worth knowing: because the mark is made before development, it is present on the latent image and will appear however the film is processed. Nothing about your chemistry caused it and nothing about your chemistry will prevent it.

Diagnostic questions

• Is the mark darker or lighter than its surroundings on the negative? Darker is pressure; lighter is contact or a scratch.
• Can you feel or see a groove under raking light? No groove and a density change is a pressure mark.
• Is it a crescent, a few millimetres across? That shape is characteristic and is the film buckling at a point.
• Are they in groups, at one part of the roll? Cinching affects the whole coil at once, so the marks tend to appear over a run of frames rather than on one.
• Where in the roll are they? Marks concentrated at the tightly wound inner end point at cinching in the cassette; marks anywhere point at loading onto the reel.
• Did the film feel tight or reluctant when it was loaded? The answer usually settles it and nobody writes it down.
• Is it every film, from one camera? Then check the camera for transport tension.

Corrective action

None. The extra development has already happened.

Where the marks fall outside the picture area or in a region that can be printed down, the frame may still be usable.

Prevention

Never pull a loose film tight by turning the spool. If a roll feels slack in its cassette, accept the slackness; cinching it is the fault.

Load the reel dry, in a bag, without force. A film that will not feed is telling you that the reel is damp or the film is misaligned, and forcing it is what makes the crescents. Back it off and start again.

Feel the film onto both grooves at the start rather than trusting the first turns, and give the few extra turns at the end that ILFORD’s guide asks for, gently.

Do not bend or kink the film, including at the end when cutting it off the spool in the dark.

And check the camera if it is only that camera: excessive transport tension is one of Kodak’s three named causes and is a mechanical fault rather than a technique one.