Fingerprints on paper

Owned by print faults and poor maximum black. The same event with a tong instead of a finger is tong marks; the same chemistry as a splash rather than a touch is hypo spots on unexposed paper.

What you see

A print of the ridges of a finger, sharp enough to be recognisable as one, in the emulsion. It is white or it is dark, and it is never grease you can wipe away.

On a wet print handled by its surface, you may instead get a smudge or a shiny patch where the soft emulsion was pressed rather than a ridge pattern.

Likely causes

1. A hand that had been in the fixer touching paper before development. The mark is white.
2. A hand that had been in the developer touching dry paper. The mark is dark.
3. Handling a wet print by its face rather than by its edges, which marks the soft emulsion physically.
4. No rinse and no towel between the wet side and the dry side.

What is happening: the chemistry and physics

A photographic fingerprint is a chemical print, not a greasy one, and that is why it is permanent.

Photographic paper carries silver halide in gelatin. A finger that has been in the fixer carries thiosulfate; where it touches, the halide is dissolved, and it is dissolved fast — ILFORD’s rapid fixer clears a paper emulsion in 30 seconds at 1+4 with full access to it, and a fingertip’s worth pressed into a dry emulsion has plenty of time before the sheet is printed. At that spot there is nothing left to expose or develop, so the print shows paper white in the shape of the ridges, and more exposure does not touch it.

A finger that has been in the developer does the opposite: it develops the halide at that spot, producing a dark ridge pattern that appears when the sheet is developed properly and is likewise unaffected by exposure.

On a wet print, a third mechanism operates: the swollen gelatin is soft, and pressure marks it physically as well as chemically, so a firm touch on a wet print leaves a shiny or dulled patch even when the hand was clean.

!The confirming test, and it is the same one as for hypo spots

Take a sheet from the same box, expose it to full room light, and develop it fully.

A normally handled sheet goes to a uniform maximum black. A sheet carrying a fixer fingerprint shows it as a white ridge pattern on that black, because there was nothing there to develop.

A developer fingerprint will not show on such a sheet, because everything went black anyway; it shows instead on a normally printed sheet as a dark mark that is present at every exposure.

Either way, the property that identifies the fault is the same: the mark does not respond to exposure. Anything that gets lighter when you print lighter is not this.

Diagnostic questions

• White or dark? White is fixer; dark is developer.
• Does it survive a change of exposure? If it does, the halide at that spot was removed or developed before the enlarger was involved.
• Are the ridges recognisable? A ridge pattern is a dry-contact mark; a smudge is a wet-handling mark.
• Where on the sheet? At a corner is where a sheet is taken from the box; in the middle is where it was held flat.
• On more than one sheet from the same box? Then the packet was handled with wet hands, and the rest of the box is suspect — test one.
• Is there a rinse container and a towel on the wet side? Kodak’s own layout recommendation asks for both.
• Was the print handled by its face when wet?

Corrective action

None. In every case the chemistry has already happened or the gelatin has already been marked.

Spotting disguises a small dark mark on a finished print; a white mark on a light ground is harder and a white mark in a black area is nearly impossible to match.

Test the rest of the packet before printing anything that matters on it.

Prevention

Separate wet and dry, and behave as though they were different rooms. Kodak’s Z-133 makes it a facility recommendation: the dry area for enlarging, printing and handling film, negatives and paper; the wet area for mixing and all processing.

Keep a container of water and a clean towel on the wet side, and use both before touching paper. This is Kodak’s own instruction and it exists because the fault is common enough to be worth printing.

Handle prints and negatives by the edges only — which is ILFORD’s instruction for negatives in the first-film guide, and the Library of Congress’s for photographs in general: freshly washed hands, clean lint-free cotton or inert plastic gloves such as nitrile, and no contact with the image surface at all.

Support a print rather than flexing it when it has to be moved or turned, per the same guidance: a piece of rigid board under it rather than a hand in the middle of it.

And use tongs for everything wet, gripping at the very edge, so that hands stay out of the trays altogether. Tong marks is the fault you are trading against, and one tong per tray prevents it.