Edge fading from mount and adhesive

Owned by Break/Fix — the printed-out image that faded, whose third case sorts the fault by geometry exactly as this entry does — a coating fault is there from the start, a washing fault follows the tray, and a mount fault follows the mount — and adds the one treatment in the whole cluster that Reilly calls proven in practice: removal from a defective mount and careful remounting, which reverses nothing already done. The albumen print as an object owns the mount as an agent of decay, and records that about 95 per cent of albumen prints were mounted at the time of production. This entry was written earlier from Part XII’s permanence lesson.

What you see

Damage with the shape of the mount, not the shape of the picture. A band of fading or discolouration following the edges of the print; a rectangle where a window mat overlapped; reddish spots — foxing — scattered across the sheet; or brittleness that begins at the mounted edge.

IPI’s guidance carries the example that makes the diagnosis obvious once it is seen: a print whose edges mirrored under a poor-quality mat while the uncovered oval stayed clear. Wherever the mount touched, the print suffered; wherever it did not, the print did not.

Likely causes

1. A lignin-rich mounting board. Reilly’s account of nineteenth-century boards is precise: thin top and bottom layers of relatively good paper laminated to a thick core of pulp containing a high percentage of lignin, whose decomposition products migrate through the top layer and attack the photograph.
2. A decomposed adhesive. Reilly names putrefied starch or gelatin pastes as producing the same kinds of deterioration.
3. The mat, the backing board or the frame. IPI’s mechanism does not require contact with the mount at all: poor framing materials behave like air pollution.
4. Mould or fungus on the mount, which Reilly names as the source of foxing and of stains.

What is happening: the chemistry and physics

A photograph in a frame is in a small closed atmosphere with whatever the frame is made of. That is the whole idea, and everything else follows from it.

Lignin degrades, and its degradation products are acidic and oxidising. Reilly’s outcome list is staining, brittleness, and accelerated fading and yellowing of the silver image. The Library of Congress make the same point about the atmosphere generally: air pollution produces nitric and sulfuric acids that attack all components of photographs, cause silver images to fade, and cause supports to discolour and become brittle. A lignin-cored board is a private source of the same chemistry, held against the print.

The mechanism for the mirroring half is IPI’s, and it is the same two-step as in the printed-out print entry: an oxidation that fades the image, followed by migration of the faded silver to the surface, followed by its conversion back to metallic silver by other pollutants. The mount supplies the first pollutant and the air the second.

And the scale of exposure is what makes mounts matter so much. Reilly notes that approximately 95 per cent of all albumen prints were mounted at the time of their production — so for that process the mount is not an accessory, it is part of the object.

!The confirming test: does the damage follow the mount or the image?

Take the print out of the frame — carefully — and compare the covered and uncovered areas.

• Damage follows the mat opening, the mount edge, or a tape line: the enclosure is the cause. IPI’s oval example is the archetype.
• Damage follows the image — worst in the shadows, or uniform across the sheet: the cause is internal, and residual thiosulfate or residual silver is the entry.
• Reddish spots unrelated to either: foxing, which Reilly associates with mould and fungus on the mount.

Then test the materials rather than trusting their labels. IPI’s own warning is blunt: acid-free, archival, museum-quality and conservation board are marketing terms that are neither standardised nor legal. The test that means something is the Photographic Activity Test, ISO 18916, which screens for the oxidation and reduction reactions that cause image fade, silver mirroring and red or gold spots.

And remember the exception this course carries. A cyanotype must go into an unbuffered mount, because the alkaline reserve that protects every other print destroys Prussian blue — see the alkaline bleaching entry. “Archival” is process-dependent here.

Diagnostic questions

• What is the board made of, and does it have a core? A laminated board with a coloured core is Reilly’s description of the problem.
• What is the adhesive? A starch or animal-glue paste of unknown age is a suspect.
• Has the print been framed, and with what backing? IPI treat framing materials as chemistry.
• Does the damage stop at a line? Lines mean enclosures.
• Is the paper brittle as well as stained? Reilly and the Library of Congress both list brittleness with the staining, which points at an acidic support rather than at the photograph.
• Which process is the print? The right enclosure differs, and a cyanotype’s requirement is the reverse of everyone else’s.

Corrective action

Remove it from the defective mount and remount it properly. Reilly is unusually definite: this is the only technique for the preservation of albumen prints that has proven itself in practice — and equally definite about its limit: remounting does nothing to reverse the deterioration that has already occurred.

This is conservation work, not darkroom work. Removing a print from a nineteenth-century mount can destroy it, and the course records that the repertoire of treatments available to photographic conservators for these materials is limited. If the object matters, it goes to somebody who does this for a living.

Support rather than flatten anything that has become brittle — the Library of Congress recommend stiff card supports beneath brittle or broken photographs, and cracked emulsion from flattening is what happens otherwise.

Prevention

Buy enclosures that have passed ISO 18916, and disregard the adjectives.

Match the enclosure to the process, buffered or unbuffered as the image substance requires.

Use a known adhesive, or none. Corner mounts and sink mats hold a print without gluing it, and an adhesive that is never applied cannot putrefy.

Keep the atmosphere clean, cool and dry, which is the one control that acts on every mechanism on this page at once.