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Revised 19 May 2005

Archival Processing of Prints

by Ed Buffaloe

Silver halides are the most sensitive materials available for use in photographic emulsions, but unfortunately metallic silver oxidizes very readily, so that silver images formed in our photographic negatives and prints require protection or stabilization in some way.  Archival processing involves fixing film and paper adequately to remove unexposed silver halides, washing appropriately to remove excess fixer, and preferably treatment with some sort of toning or sequestering solution to prevent the emulsion silver from oxidising in the presence of various environmental pollutants.  In this article, I am primarily concerned with photographic prints rather than negatives.

Fixing: Adequate fixing is necessary to remove unexposed silver halides, which, if left in place, would react with light and degrade the image.  Most practitioners today use Ilford’s processing method for prints, which specifies rapid fix (with ammonium thiosulfate instead of sodium thiosulfate) at “film” strength, i.e., diluted 1:3 or 1:4 instead of the old “paper” dilution of 1:7, for about one minute (compared to the 5 to 10 minutes required in a sodium thiosulfate fix). The concentrated ammonium thiosulfate provides adequate removal of unexposed silver halides while reduced time in the solution prevents fix from penetrating into the paper base where it is very difficult to remove.  Photographers would do well to remember that over-fixing of prints is equally detrimental Click to go to Amazon.comto archival quality, in the long term, as under-fixing.  My personal method for prints is to utilize two trays of rapid fix, agitating the print in each tray for 30 to 45 seconds.  When the second tray of fix has reached half its recommended capacity, it moves to the first tray and I prepare a second tray of fresh fixer.  The two-tray method increases the useful life of the fix by reducing contamination in the second fix, assuring adequate fixation.  Kodak’s “Residual Silver Test Solution ST-1” may be used to determine if paper or film is properly fixed.  I should note that the traditional method of fixing prints in a sodium thiosulfate solution for 5 to 10 minutes is perfectly acceptable, so long as fixing and washing times are adequate.

Washing: Adequate washing is necessary to remove residual thiosulfates (fix) in the print, which could otherwise cause the print to deteriorate over time.  However, recent studies at the Rochester Institute of Technology’s Image Permanence Institute (RIT IPI) indicate there may be as much danger in over-washing as in under-washing.  Doug Nishimura of RIT states, “...it has been proven at Kodak, Fuji and here at IPI that a small amount of hypo will make photographs MORE stable against air pollutants and that overwashing decreases the stability.”  He is referring to untoned silver images.  He further states that, since it is difficult to wash until the optimum amount of residual thiosulfate remains for perfect preservation of the silver image, IPI recommends an after-treatment to convert image silver to something more stable.  Over-washing can also leech out the optical brighteners that are added to most modern papers.

With the use of a wash aid such as Kodak Hypo Clearing Agent, Orbit Bath, or Perma Wash, the time required for washing prints can be reduced to a half-hour or less, assuming that Ilford’s method of rapid fixing has been followed.  (I personally do not use Perma Wash for prints, though I do use it for film.)  Kodak’s “Hypo Test Solution HT-2” may be used to determine (approximately) if paper or film has been properly washed.  To test for uniform washing of paper, develop and fix a blank, unexposed piece of paper.  Then test various portions of the paper with HT-2 test solution.  Because of the variability of water quality and print washers, the only way to ascertain if washing is adequate is to test (see test description below).  I strongly recommend turning your prints 180 degrees halfway through the wash cycle to increase uniformity of washing.

Toning:   Perhaps the most shocking discovery of the past couple of decades has been that the noble metals in many popular toners do not always provide adequate protection for silver images.  Silver is only protected from oxidation to the extent that it is completely replaced or plated over by a more stable element (gold, platinum, or palladium) or forms a more stable compound (such as silver sulfide or silver selenide). Experiments at RIT’s IPI, which involved toning microfilm in Kodak Gold Protective Solution (GP-2), indicate that this solution is equally effective for microfilm when the gold chloride is omitted..  This came as a surprise, since researchers had long assumed that gold was the active protective agent.  IPI test results indicate the thiourea (thiocarbamide) in the formula is the effective ingredient, converting image silver to stable silver sulfide.  While sulfides are the chief pollutants which cause image degradation, the complexes they form with ionic silver are quite stable; therefore, IPI has determined that the best protection for silver film images is intentional sulfiding.  However, Liam Lawless tested Kodak’s Gold Protective Solutions with a contemporary enlarging paper, and his results indicate that the gold is a necessary ingredient for fiber papers.  (See Testing Gold Protective Solution.)  Liam’s results also indicate that GP-2 is more effective than GP-1, at least in the chromic acid bleach test that he used.

Platinum is rarely used as a toner for silver gelatin papers, due to its expense.  However, it does see some use for toning kallitypes, where the total quantity of silver to be toned is somewhat less than in a gelatin silver print.  Luis Nadeau notes that experiments performed by Ilford in the 1970’s with a very old platinum toner formula caused image destabilization, but he was did not provide details as to the exact toner formula or the exact problems encountered.  Platinum is considered to be the most stable noble metal other than gold, and it definitely merits further testing.  Platinum gives a very neutral black image when used to tone silver prints.

Click to go to Amazon.comSelenium remains the most popular toner among fine art photographers.  It converts silver to silver selenide, and causes a color shift with most papers, ranging from purple with bromide papers to reddish-brown with chloride papers, which many people find quite pleasing.  Doug Nishimura cautions that partial toning or split-toning with selenium will leave the untoned portion of the print unprotected, as the selenium preferentially tones finer grains of silver in high-density areas of the print first.  Untoned portions of the image may be subject to future deterioration.  This flies in the face of longstanding advice from Kodak which, as repeated by Ansel Adams and many others, said that selenium provides protection even in very high dilutions which do not cause color changes.  Apparently at one time Kodak Selenium Toner may have contained “small amounts of highly active sulfiding agents” which provided protection that selenium alone cannot provide unless toning is carried to completion.  At some point in the 1980’s manufacturing changes eliminated these agents.  Doug Nishimura indicates (in a letter to Jennifer Scott) that complete protection with Kodak Selenium Toner requires a dilution of not more than 1:9, and a toning period of 3 to 5 minutes at 68º.  Some fine art photographers find this depth of toning not to their taste.

Kodak Polytoner, which contains both selenium and sulfide, is probably more effective than selenium toner alone for archival purposes, but I personally have never been able to obtain precisely the tones I desire from it, and it is no longer made by Kodak..

Sulfide and polysulfide toners (brown and sepia toners) always transform print color to a brown or yellow-brown, but the resulting image is quite stable.

Other Treatments: Agfa makes a product called Sistan, and Fuji makes a similar product called AG Guard, which is used to treat prints after washing.  Thomas Wollstein has corresponded with Agfa regarding Sistan, and tells us that Sistan contains potassium thiocyanate and a wetting agent--it works by converting oxidized silver ions in the emulsion to a stable, insoluble salt.  Robert Chapman states that Sistan “...precipitates any silver ion formed by oxidation in the form of silver thiocyanate (AgSCN).  Silver Thiocyanate is colorless and virtually light-insensitive.”  But Sistan only works as long as the thiocyanate stays in the emulsion, so Agfa recommends that Sistan be used as a final treatment, after washing and before drying--if it is washed out, archival benefits are probably lost.

According to Doug Nishimura, “before any silver deterioration can occur, silver must be oxidized into silver ion.  Even air and moisture can act as a strong enough oxidizing combination to cause damage.”  He notes that “...there is always a small amount of ionic silver in equilibrium with silver metal in a photographic image.”  But, whether the ionic silver already exists in the emulsion or is caused by pollutants, thiocyanate combines with it, thereby stabilizing it as an inert salt which will not cause image degradation.  Sistan is said to be fully compatible with toning treatments.  I should note that Dupont 6-T Gold Toner contains potassium thiocyanate, and Kodak GP-1 contains sodium thiocyanate, but I do not know if either is in sufficient quantity to be as effective as Sistan is alleged to be--also, prolonged washing would negate any benefit derived therefrom.  Robert Chapman states that, though he has inquired several times, Agfa has not provided him with substantive documentation to prove the effectiveness of Sistan. He allows, however,  that “..it makes sense on theoretical grounds.”  Other sources on the world-wide-web hint that Sistan may not be effective over the long term, but there is no hard data to back this up either.

Long Term Stability:  Doug Nishimura of RIT’s Image Permanence Institute has emphasized repeatedly that image permanence is tied more to storage conditions than to processing.  No matter how carefully processed an image is, if it is subjected to atmospheric pollutants it will be liable to degrade.  In a letter to Jennifer Scott of the State Library of South Australia, he tells an anecdote about photographic prints on display in a gallery that suffered deterioration in a matter of weeks in the form of orange spots, which resulted from the fumes produced by a repainting of the gallery walls prior to the exhibit.  In a web post he states:  “...we find that of the thousands of photographs examined here at IPI, we rarely find deterioration from hypo retention.  Virtually all of the fading seen in photographs has been caused by [contaminants in] air and moisture.”

In the November/December 2000 issue of View Camera, Michael A Smith published a very interesting article entitled “Advances in Archival Mounting and Storage:  Ultimate Protection for Your Photographs,” which is an interview with Bill Hollinger.  In this interview Mr. Hollinger discusses the ArtCare mounting board which he invented .  ArtCare board is designed to absorb and sequester environmental pollutants, preventing them from attacking photographs.  When queried as to where such pollutants come from, he stated:  “The acids are emitted by wood, plywood, particle board, and chipboard, and the formaldehydes are emitted by carpets, draperies, upholstery, and certain plastics.  In addition, sunlight entering a building causes the buildup of ozone, peroxides, nitric acid, and other nitrogen-containing molecules...”  Dramatic examples of accelerated aging tests are shown in the article. Judging from the examples, ArtCare board  appears to be superior to 100% rag board for long-term preservation.  Test results also indicate that dry-mounted prints, no matter what board they are mounted on, fare better than prints that are hinged or corner-mounted.  The dry mount tissue serves as a barrier to pollutants that have been absorbed by the mount board.

Testing for Residual Silver After Fixing

If your photographic materials still contain silver compounds after fixing, those compounds will eventually break down or react with other chemicals and cause image degradation. To test your prints or films for adequate fixing, mix the following formula:

Kodak® Residual Silver Test Solution ST-1
Distilled Water . . . . . . . . . . . . . . . . 125 ml
Sodium Sulfide (anhydrous) . . . . . . .   2 g
(This solution keeps for 3 months in a small tightly-sealed bottle.)

To use, dilute 1 part of the above stock solution with 9 parts distilled water.  This working solution keeps less than a week. Squeegee your print or film and place one drop of the working solution on a border area. Let it sit for 3 minutes and blot with a clean cloth or tissue. Any discoloration other than a barely-visible cream tint indicates that your print or film still contains silver halides that require further fixing to remove.


[Information taken from Processing Chemicals and Formulas for Black-and-White Photography, Kodak Publication No. J-1, Eastman Kodak Company, 1973.]

Testing for Adequate Washing

If thiosulfate compounds (hypo or fix) are not washed out of your photographic materials, they will eventually begin to react with the silver in the image and cause image degradation. To test your prints for adequate removal of thiosulfate compounds, mix the following formula:

Kodak® Hypo Test Solution HT-2
Distilled Water . . . . . . . . . . . . . . . . . 750 ml
28% Acetic Acid . . . . . . . . . . . . . .  .125 ml
Silver Nitrate, Crystals . . . . . . . . . . . . 7.5 g
Distilled Water to Make . . . . . . . . . . .    1 l
(Store in a tightly sealed brown glass bottle away from strong light sources.  This solution stains everything it touches, so don’t splash it around.)

To use for paper, place one drop on the border of the print, let it stand for 2 minutes, then rinse with water.  If the print is thoroughly washed the solution will produce only a very faint tea-colored stain, or possibly no stain at all.  If it is inadequately washed, the solution will produce a rather dark tea-colored stain. To judge the stains accurately you should purchase a Kodak® Hypo Estimator, which costs about $3.

To use for film, cut off a small piece of film and drop it into the test solution for 3 minutes.  Properly washed films should show virtually no discoloration.

Testing for Fixer Exhaustion

If your fixer is exhausted, you will not obtain adequate removal of thiosulfates from your paper.  To test your paper fixer, use the following formula:

          Kodak Fixer Test FT-1
          Potassium Iodide . . . . . . . . . . . . . . .  190 g
          Distilled water to make . . . . . . . . . . . .    1 l

To use: To 5 drops of KODAK Fixer Test Solution, FT-1, add 5 drops of the fixing bath to be tested and 5 drops of water. Discard the fixer if a yellow-white precipitate forms instantly. Any slight milkiness should be disregarded.  Do not use this solution for testing film fixer.

For acceptable washing, the test spot should be no darker than the comparison patch.  Different films and papers may produce differing amounts of stain.  In general, the stain should be somewhere between 1 and 2, but for certain materials a darker stain is acceptable.  In my personal testing of various papers, the stain has generally been at the level of patch 1 or less.  In some cases, I have had no stain at all.  Don’t try to judge your photographic materials using this reproduction, as monitors vary in their ability to render color. Kodak cautions that this estimator is only for use with products processed with Kodak Hypo Clearing Agent, and that other wash aids may give differing results.  “This test procedure does not conform with the ANSI Method of determining residual thiosulfate levels.”   For a quantitative test of residual thiosulfate, you must use the methylene blue method (ANSI standard PH4.30-1969).

Capacities and Keeping Properties of Rapid Fix

Ilford does not provide information regarding the number of films that can be fixed  per volume of fixer.  They recommend fixing film in either their Universal fixer (diluted 1:3) or Multigrade fixer (diluted 1:4) for 2 to 5 minutes. They state:  “In general, fix film for twice the time it takes for the emulsion to clear.  If working with used fixer, discard if films do not clear within half the recommended fixing time.”  They also state that there is no harm in overfixing films.

Ilford states that one liter of working strength Multigrade fixer (1:4 dilution) will process up to 50 8x10 inch prints.  Unopened bottles of Multigrade fixer will keep for two years, while tightly-capped partially full bottles will keep for six months.

Kodak states that one quart or liter of their Rapid Fixer (diluted 1:3) will process 32 8x10 inch negatives, and that a similar quantity diluted 1:7 will fix 26 8x10 inch prints.  Further, stoppered bottles of Rapid Fix at working solution will keep for two months. Kodak’s film fixing recommendations are nearly identical with Ilford’s.  Kodak recommends fixing papers for 5 to 10 minutes (1:7 dilution) in a single bath, or 3 to 5 minutes each in two fixing baths.

My Personal Archival Processing Procedure

  • 1.  Fix in 2 baths of non-hardening rapid fix at “film” strength (usually 1:3, 1:4 for Ilford) for 30 to 45 seconds each.
  • 2.  Wash for 5 minutes in a tray with a siphon.
  • 3.  Soak in hypo clearing agent for 3 minutes with agitation, or 10 minutes without agitation.
  • 4.  Wash for 30 minutes or more in an archival print washer.  My prints stay in the wash until the end of the printing session (sometimes up to 3 hours).
  • 5.  Tone in selenium, or brown toner, or (more rarely) gold toner--times vary.
            a. With selenium toner on a warm paper, I usually use a dilution of 1:15 and tone for 1 to 5 minutes.  Recently I’ve preferred moderate toning for only a minute or two, but if I want a strong color change I may tone fully.  At this dilution it might take 5 to 10 minutes for a print to be fully toned (hence closer to archival perfection), but at some point I feel it is more important for the print to be expressive than 100% archival.
             b. Brown toner, I use per Kodak’s instructions, though sometimes (when I double tone with selenium first) I reduce the times considerably to obtain a split tone effect with chloride papers.  Times are from 1 to 20 minutes.  Brown toner keeps toning in the wash unless toning is immediately followed by a bath of hypo clearing agent (even then, some color changes may take place in the wash).
             c. Gold toning takes place at about 100 degrees for 3 to 5 minutes.
  • 6.  Soak in hypo clearing agent for 3 minutes with agitation.
  • 7.  Wash in archival print washer for 2 hours.  If I go to a movie, washing might last 4 or 5 hours (though I turn the water flow down).  I arrived at my print washing times by testing with Kodak HT-2.  After 2 hours there is no stain whatsoever with the many papers I use.  I have read that long wash times can leach out optical brighteners, but I’ve never been able to tell the difference between 2 and 6 hours in a cold wash.
  • 8.  Dry face up on clean fiberglass screens.  The screens can be cleaned periodically with a mild chlorine solution and rinsed thoroughly with water.  I used to dry face down, but experienced problems with the screen imprinting on the print surface.  Since I began to dry face up, I have been placing a fan to blow air onto the prints, indirectly, from below.
  • 9.  Dry mount on 100% rag museum board.  I’ll switch to ArtCare board when I run out of the museum board.

References

Stability of Black-and-White Photographic Images, with Special Reference to  Microfilm, by James M. Reilly, Douglas W. Nishimura, Kaspars M. Cupriks, and Peter Z. Adelstein, Abbey Newsletter, Volume 12, Number 5, July 1988, available at http://palimpsest.stanford.edu/byorg/abbey/an/an12/an12-5/an12-507.html.

Various posts by Doublas W. Nishimura and Luis Nadeau on a mail distribution list of the RIT Image Permanence Institute at
http://palimpsest.stanford.edu/byform/mailing-lists/cdl/1993/author.html.

I am indebted to Jennifer Scott of the State Library of South Australia for sharing a letter from Doug Nishimura on archival processing of film and prints.

“Ist doch bloß Plastik! Oder: Sind Fotos auf PE-Papier so stabil wie solche auf Barytpapier?”, Schwarzweiss-Mag@zin.De,
http://www.sw-magazin.de/swmag_frame_wollstein.htm

“Preserving Prints”, by Robert Chapman, in the “Photochemistry” column of Photo Techniques, Vol. 22, No. 1, May/June 2001, p. 11.

“Advances in Archival Mounting and Storage: Ultimate Protection for your Photographs,” by Michael A. Smith, View Camera, November/December 2000, pp. 48-53.

Ilford technical data sheets for film and paper, available at
http://www.ilford.com/html/us_english/homeng.html.

Kodak Professional Black-and-White Films, publication number F-5.

Kodak Processing Chemicals & Formulas for Black-and-White Photography, publication number J-1.

The Compact Photo Lab Index, edited by Ernest M. Pittaro, Morgan & Morgan, 1979.

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