Emulsion-side scratches

Owned by the emulsion under stress, which sets out the side-of-the-base question in full. This entry and base-side scratches are two halves of one diagnosis.

What you see

A line — usually long, usually straight, often running the length of the film — that is lighter than its surroundings on the negative and prints as a black line.

Under a loupe focused on the emulsion surface it is sharp; focused on the base surface it is not. Under raking light it is a groove.

Likely causes

1. A squeegee or chamois with grit in it, drawn down a wet film. This one fault can take a whole roll in a single second.
2. Contact with anything while the layer was swollen — the edge of a tank, a fingernail, a hanging clip.
3. A processor’s rollers, racks or squeegees, dirty or misaligned, which is Kodak’s laboratory version.
4. Careless handling of the dry negative afterwards, including a sleeve with grit in it.

What is happening: the chemistry and physics

A swollen gelatin layer is soft. Something harder drawn across it removes material, and the material it removes contains the image silver.

That is what makes this the worse of the two scratches. The picture in that line is gone; there is less silver where the groove is, so the negative is more transparent there and the print is darker. Nothing put into the groove can replace what is not there.

!Which side is it on? Two tests, both free

The loupe test. Focus a loupe on the emulsion surface and then on the base surface. The scratch is sharp on the surface it is in. On 35 mm film the two surfaces are only about 0.125 mm apart — ILFORD’s published base thickness for HP5 Plus — so use a good loupe and take your time.

The wetting test. Put a little clean water on a swab and wet the base side over the mark. A base-side scratch all but disappears, because filling the groove with a liquid of similar refractive index stops it bending light. An emulsion-side scratch does not change, because it is a loss of silver rather than a distortion of the light path.

And the print tells you too. Emulsion-side scratches print black; base-side scratches print white. If you already have a print, you already have the answer.

The consequence for the diagnosis is where in the chain it happened. The emulsion is only soft when it is wet, so an emulsion-side scratch was made after the film entered the developer — in the tank, in the wash, on the squeegee, on the line, or in handling afterwards. Everything before the developer is eliminated in one observation.

Diagnostic questions

• Which side, by the loupe or the wetting test? Do this first; nothing else matters until it is answered.
• Does it run the whole length of the film at a constant distance from the edge? Then something the film ran past made it, and the squeegee is the first suspect.
• Is it on this roll only, or on the last several? A recurring line in the same place is equipment.
• What was used to wipe the film? ILFORD prescribe a clean squeegee or chamois and warn that “any grit caught up here will scratch the whole film”.
• Was the film dry when it was handled? A dry emulsion is far more robust; a scratch that appeared during filing points at the sleeve or the surface it was laid on.
• Are there several parallel lines? That is a blade or a roller, not a single accident.

Corrective action

Nothing that restores the silver.

At the printing stage, a diffusion enlarger’s scattered illumination makes a scratch less obtrusive than a condenser’s directional beam does, and the print can be spotted — a black line on the print is filled with bleach or knifed by a retoucher, which is skilled work and imperfect at any scale above a hairline. The Library of Congress lists marking an original with ink and repairing it with pressure-sensitive tape among examples of negligence: retouch the print, never the negative.

Prevention

Stop using the squeegee, or make it a clean one every time. ILFORD’s own instruction offers both routes in the same sentence — squeegee tongs or a clean piece of chamois — and the operative word in both is clean. A squeegee rinsed under the tap before every film costs five seconds; a chamois kept in a closed jar is better than one on a hook over a bench.

Or dry without wiping at all, which is what many careful workers do: a final rinse in correctly diluted wetting agent, drained rather than wiped, hung in a clean still place at 30–40 °C or at room temperature. Drying marks is the fault you are trading against, and the wetting agent is what makes the trade safe.

Hang film where nothing can swing against it, and cut it only when it is completely dry.

Handle dry negatives by the edges, with clean hands or gloves, and support a sheet rather than flexing it — which is the Library of Congress’s own instruction for archival material and is no harder for yours.