Tong marks

Owned by print faults and poor maximum black. Its close relative is fingerprints on paper, which arrives by the same routes with a different implement.

What you see

Small marks in pairs, at the point where the tongs gripped: usually near an edge, usually two of them opposite each other, sometimes a short parallel pair from a flat-jawed tong.

They are either lighter or darker than their surroundings, and which one they are is the whole diagnosis.

Likely causes

1. A tong used in more than one tray. The commonest cause by a distance.
2. Pressure on a soft wet emulsion at the grip point.
3. A tong gripping inside the image area rather than at the very edge of the sheet.
4. A tong laid on a wet bench and then used to handle dry paper.

What is happening: the chemistry and physics

Two entirely different mechanisms produce a mark at the same place, and they are told apart by the direction of the density change.

Chemistry carried on the tong. A tong that has been in the fixer and then grips a sheet in the developer puts thiosulfate at that point. Thiosulfate dissolves silver halide, and it does it quickly — ILFORD’s rapid fixer clears a paper emulsion in 30 seconds at 1+4 — so the halide at the grip point is removed before it can be developed. The mark is lighter, sharp-edged, and unaffected by exposure.

A tong that has been in the stop and grips a sheet in the developer does something milder: it lowers the pH locally, so development is slowed rather than prevented, and the mark is a softer light patch.

A tong that has been in the developer and grips dry paper does the opposite: it develops that spot, and the mark is darker.

Pressure on the wet emulsion. A firm grip on a swollen gelatin layer deforms it and, if the grip happens before or during development, can also change how the emulsion there responds. That mark is a density change without any chemistry carried in, and it is generally darker — the same plus-density effect Kodak’s table records for pressure marks on film.

!Light or dark? That is the whole diagnosis, and it takes one look

The mark is	What the tong had been in	Recoverable?
Lighter, sharp-edged, survives more exposure	The fixer	No — the halide is gone
Lighter, softer, less pronounced	The stop bath	No, but the effect is smaller
Darker	The developer, or pressure on a wet emulsion	No

And the confirming test for the fixer case is the same as for hypo spots: a mark that stays white however dark you print the sheet had its silver halide dissolved before exposure, and no printing decision touches it.

Diagnostic questions

• Lighter or darker than the surroundings? The table above.
• Where exactly? At the extreme edge, or inside the picture? Grip position is a habit and a fixable one.
• Are there two, opposite each other? That is a tong rather than a finger.
• Is the same mark in the same place on several prints? Then it is the way you hold them, not an accident.
• Is there one tong per tray, and are they marked?
• Was a tong laid on the bench between uses? A wet bench is a shared bath.
• Does the mark survive more exposure? If it is light and it does, it is fixer.

Corrective action

None on the print. In every case the mark is a chemical or physical event that has already completed.

Where the mark is at the extreme edge, trimming or mounting may remove it, which is why gripping at the very edge is worth doing even when tong marks are rare.

Spotting can disguise a small dark mark on a finished print. A light mark is harder, because filling a white spot on a light ground is easier than matching a mid tone.

Prevention

One tong per tray, marked, and never moved. This is the entire prevention for the common case, and it costs the price of a second and third pair of tongs. ILFORD’s general instruction is the same principle at the mixing bench: dedicated equipment wherever possible, everything washed after use.

Grip at the very edge of the sheet, outside the image area, so that an occasional mark falls where it does no harm.

Grip lightly. A wet emulsion needs very little force to hold and very little to mark.

Never lay a tong on the bench. Rest it on the rim of its own dish or in a holder beside it.

And rinse and dry your hands between the wet side and the dry side, per Kodak’s own darkroom layout recommendation — because the same tongs are usually accompanied by the same hands, and fingerprints on paper is the other half of this fault.