Toner penetration at the edges of an RC print

Owned by Lab: bleaching and redeveloping a sepia print, whose troubleshooting table sends a darker band inside the trimmed edge here, and which treats edge penetration as an expected observation of its own published sequence rather than as a mistake, because that sequence adds up to more wet time than a resin-coated sheet tolerates. Selenium toning and the print curve builds the trimmed margin into its test target for the same reason. This entry was written earlier from Kodak’s G-23 and from the construction of the paper.

What you see

A band of discolouration creeping inwards from the cut edges of a resin-coated print — often a millimetre or two, sometimes far more — while the middle of the print is toned exactly as intended. On a print trimmed to the image, the band is in the picture.

It appears at the cut edges specifically, not at the manufactured edge of a sheet, and that is the diagnosis.

Likely causes

1. Time — and the clock that matters is the whole wet sequence, not the toner alone. Kodak’s instruction is to keep toning times for resin-coated papers to a minimum, and their threshold for the countermeasure is a toning time longer than 8 to 10 minutes. ILFORD set the limit on the other quantity: prolonged immersion causes edge penetration and curl on resin-coated paper, so wet times longer than 15 minutes should be avoided. Read together they explain why a printer who never exceeded Kodak’s toning figure still meets this fault — a published bleach-and-redevelop sequence reaches ILFORD’s limit without any single bath being long, which is why Part XX’s sepia lab treats edge penetration as an expected observation of its own procedure and builds a trimmable border into it.
2. Cut edges, which are the route.
3. Insufficient washing afterwards — Kodak note that it is difficult to wash toner from the edges of a print, which is why the remedy they offer is trimming rather than washing.
4. No border to spare. A print trimmed to the image before toning has nowhere for the damage to go.

What is happening: the chemistry and physics

A resin-coated paper is a paper core sandwiched between two polyethylene layers. That construction is why it fixes and washes so quickly: the base does not absorb the processing solutions, so only the thin emulsion has to be cleared, and Kodak’s wash figure is four minutes in running water against an hour for fibre-base.

But the sandwich is open at the edge. Wherever the sheet has been cut, the paper core is exposed as a thin line all round the print. Liquid reaches it there by capillary action along the fibres, and once it is in, the resin that keeps solutions out also keeps them in: there is no path for the wash water to follow that the toner did not already take, and no reservoir of swollen gelatin to carry the residue out.

So the fault is a construction consequence rather than a chemistry failure, and it explains both halves of Kodak’s advice. Keep the time short, because penetration is a diffusion process and diffusion is slow. And if you must tone long, leave a border you can cut off, because the one thing that reliably removes toner from the edge of an RC print is scissors.

!The confirming test: look at which edges, and compare with fibre

Examine the border under a lamp and ask where the discolouration starts.

• At every cut edge, uniformly, running inwards: this fault. The geometry follows the knife.
• At the borders and highlights generally, as a dark yellow stain: not this. Kodak attribute that to an exhausted fixing bath leaving insoluble silver compounds that a toner then reacts with — see uneven toning and the exhausted fixer.
• In round spots: air bubbles in the fixer.

Then tone a strip with three cut edges and one factory edge. If the discolouration appears at the three and not at the one, the route is confirmed and no further test is needed.

Diagnostic questions

• How long was the print in the toner? Kodak’s own threshold for taking precautions is eight to ten minutes.
• How wide is the border? A generous border converts this fault into a trimming operation.
• Was the print washed for long enough afterwards? Four minutes in running water with a complete change of water, on Kodak’s figure, and note that they do not recommend Hypo Clearing Agent with resin-coated papers.
• Is it fibre or RC? A fibre print absorbs everywhere and shows a different family of faults; this one is specific to the sandwich.
• Was the sheet cut before or after toning? Cutting afterwards is the whole remedy.

Corrective action

Trim it off, which is Kodak’s own answer and the reason they tell you to leave the border in the first place.

If there is no border to trim, the print is finished. Re-print with a margin.

Do not try to wash it out. Kodak state that it is difficult to wash toner from the edges of a print, and extending the wash on an RC print buys very little because the base was never absorbing water in the first place.

Prevention

Keep RC toning times short, and use a more concentrated bath for a shorter time rather than a weak one for a long time, within the toner’s own published dilutions.

Always leave a border and trim after toning. It costs a strip of paper and it removes the fault entirely.

Consider fibre-base for work that needs long toning, which is a different set of trade-offs and not a different set of faults — see uneven toning for what fibre brings instead.