Clearing an iron-silver print and testing it for residual iron

Purpose

To get the iron out of a printed iron-silver sheet before it dries, and to end holding a stated observation about what is left rather than a hope.

When to use it

Every Van Dyke and kallitype print, after development and before fixing, because toning has to follow clearing and precede fixing, and because the iron must be gone before the print dries.

Then again after fixing and washing, since the fixer and the wash can redistribute what is left and the test costs nothing.

Before you start

You should already know why the first clearing bath has to be acidic and why an alkaline one at pH 10 precipitates iron(III) rather than chelating it, from the clearing lesson.

Level B. The clearing agents themselves are mild at these strengths; what sets the level is the noble-metal toner if you use one, the hexacyanoferrate reagent, and the metal in every bath. Nitrile gloves changed rather than wiped; splash goggles for a toning stock and for making an alkaline EDTA bath; safety spectacles otherwise; non-metal tongs.

One raised step, declared here. Handling the concentrated gold or palladium stock is above the rest of the session and carries its own controls: gloves and splash goggles, the bottle opened over a tray, a dedicated dropper, the stock never decanted into an unlabelled vessel, and any spill wiped up wet rather than left to dry. The working bath does not need that standard, and buying the toner ready diluted removes the step. A reader with a known metal sensitisation does not run the toning half and runs the clearing half, which is where most of the permanence is.

The separation rule governs the whole session. The spot-test reagent is a hexacyanoferrate and the clearing baths are acid, so the test has its own station: its own dish, pipette, blotter and waste bottle, with nothing acidic within reach and nothing from it going into the clearing-bath waste. The acid exclusion rule is the authority.

On the bench: six trays and a seventh small dish at the separate station; the 3 per cent citric acid or disodium EDTA bath, made ahead; the sulphite bath, made fresh today; the alkaline bath; blotting paper; narrow-range pH paper; distilled water for the reagent; and a coated, unexposed, fully processed control sheet of the process, carried through every bath alongside the prints.

Procedure

1. Decide which published sequence you are running and write it in the record before you start. The three are different procedures, not variants.
2. Check the rinse water with pH paper: neutral or slightly acidic. An alkaline rinse forms iron hydroxides in the fibres that make complete clearing difficult or impossible.
3. Set the test station up, physically apart, with its own everything and nothing acidic near it.
4. Note and sketch the colour of each print’s masked border before anything is wetted. That is your before-and-after.
5. Rinse one to two minutes in the checked water.
6. Drain the print before it enters the first clearing bath.
7. Bath 1, acidic, with intermittent agitation. Never an alkaline chelating bath first.
8. Rinse half a minute — not a wash, just enough to stop bath 1 travelling into bath 2.
9. Bath 2, the sulphite, which reduces what chelation alone cannot detach.
10. Rinse half a minute again.
11. Bath 3, the alkaline chelating bath, which suits the iron(II) the sulphite just made and leaves the sheet alkaline.
12. Judge the end point on the masked border, not the clock: no stain left in the sensitised but unexposed area, and no yellow or grey fog in the whites.
13. Expect the image to lighten considerably and do not respond to it. The density returns during toning and fixing.
14. Rinse thirty to sixty seconds, then tone, then fix, by the process’s own page.
15. The spot test. At the separate station, put one drop of dilute potassium ferricyanide on a highlight area of a sacrificial offcut — never on a print you are keeping, because it destroys what it touches. Blue means iron.
16. Compare the coated-but-masked border with the uncoated margin beside it as well. The spot test responds to iron from any source — a clip, a tray, hard water, the paper itself — and this comparison is what separates poor clearing from contamination.
17. Run the residual thiosulfate and silver tests on the control sheet, after the wash, and only once it has passed the iron test.
18. Route the spot-test dish, pipette and waste to the hexacyanoferrate container, and everything else by the segregation sheet. Local regulation governs what happens to each container next — check your local regulations, under the disposal caveat.

How you know it worked

• The rinse before clearing tested neutral or slightly acidic, and you read it rather than assumed it.
• The first bath was acidic and the last alkaline, in that order.
• The masked border is as white as the uncoated paper beside it, judged in a bluish light.
• The spot test on the offcut shows no blue, and the border-against-margin comparison agrees with it.
• The sulphite bath was made today.
• Nothing acidic came within reach of the test station, and its waste went to its own bottle.

If a step fails

Step 2, the rinse water is alkaline. Acidify it slightly or use distilled water. Iron hydroxides formed in the fibres are a different problem from dissolved iron, and they are not reversible by longer clearing.

Step 7, the only chelating agent you have is the tetrasodium salt. Use it as bath 3 and put a citric acid or disodium EDTA bath in front of it. A first bath at pH 10 hydrolyses the iron(III) instead of complexing it, and the eventual result is a yellow or brown stain.

Step 12, the first print of the session clears slowly. That is the paper. A print needing more than about four to five minutes is on a sheet the sources judge unsuitable; over ten minutes and it wants sizing. Neither is a fault you can wash your way out of.

Step 12, the times get longer as the session goes on. That is the developer or the bath. Rotate the clearing baths so the freshest is last, and replace bath 1: the acidic baths clear only two or three prints each.

Step 12, one print clears slowly and its neighbours do not. That print’s rinse was alkaline. Note it and check step 2 again.

Step 15, the spot goes blue. Iron is present. Prolong the alkaline bath and look at the border again; if a fresh sequence does not shift it, record the result rather than repeating the test until it passes.

Step 17, the thiosulfate test reads yellow-brown on a sheet that failed the iron test. The two stains are the same colour in the same place and cannot be told apart. Clear first, then test.

What to record

The sequence chosen and why; the rinse water’s pH; each bath’s composition, strength and how many prints it had cleared; the clearing time per print and the state of its masked border before and after; the toner and whether the raised step was taken or avoided by buying a dilute stock; the spot-test result on the offcut with the border-against-margin comparison beside it; the residual tests on the control sheet; and where each of the six streams went.