Processing RC papers Permanence of RC papers

Darius Himes <dhimes<-a t->midas< . >bwc< . >org wrote:

> I would like to know if anyone has had experience with testing fixer
> residue (sodium thiosulphate *or* ammonium thiosulphate) levels in
> Resin Coated photographic papers.
>
> I am concerned about the level of fixer present in RC papers which
> have been run through a black and white print processor (a process
> which takes 1 minute). Our institution is currently using such a
> processor, and these prints are destined for our permanent
> collection of photographs. Establishing just how much fixer residue
> these prints retain seems paramount. Are there any suggestions?

and

> I am currently researching the longevity of resin-coated
> photographic papers. Can anyone suggest any publications dealing
> with this topic, and also in relation to the longevity, in an
> archival environment, of traditional fiber-based photographic
> papers, such as those currently on the market (Ilford Multigrade,
> Brilliant, Cachet, etc.)? With many thanks,

Some years ago we investigated the market in Denmark for automatic
processing machines for RC papers. We found that all machines left a
high amount of residual thiosulfate in the prints. The residual
thiosulphate was measured by the methods described in the
ISO-417-1993 standard.

By increasing the processing times of those machines which could be
regulated the level of residual fixer could be reduced. A reduction
could also be achieved by increasing the temperature of the wash
water.

As a first conclusion we found that all available processing
machines at that time would process RC prints containing an
unacceptable high level of residual thiosulphate when used as
recommended by the manufacture.

Our preliminary conclusion was that all RC print processors
available at that time left unacceptably high levels of residual
fixer when used in accordance with the manufactures'
recommendations. However, in an attempt to improve its washing
Ilford Denmark suggested modifications to an Ilford 2240RC
processor. A spray bar was built into the washing tank and the
processing time was increased from 70 seconds dry-to-dry to 120
seconds. Further, the critical temperature for the wash water was
found to be between 25 deg C and 30 deg C. Below 25 deg C washing
was inadequate, above 30 deg C the optical brightener tended to be
washed out of the print, resulting in a slight degradation of
highlights (In any event, the optical brightener is destroyed by
exposure to daylight. This has no bearing on the archival stability
of the image). This modified machine has been in use for about five
years now and regular quality controls have not detected any
residual fixer.

Concerning the acceptable level of thiosulfate in RC prints we feel
that there should be no  measurable thiosulfate in such RC prints
after processing. On the other hand our experience also tells us,
that most problems of yellowing and discoloration in exhibited
RC-prints originates from pollutants in the atmosphere - not
residual thiosulfate. However, we have no scientific results on
this. Furthermore, we know that a high content of residual
thiosulfate from fixer can stabilise negative films, but the amount
"needed" varies between products and also between fixer formulas.

As a consequence of these observations we have decided upon
processing procedures at the Conservation Department in which all
films and prints are washed to the extent that no residual fixer is
measurable when using the methods described in the ISO 417 standard.

Furthermore, all prints whether RC or FB are protected against
pollutants by a stabilising toning treatment before they leave the
Photo Lab at the Conservation Department. We have examined several
products such as Kodak Rapid Selenium Toner, Kodak Brown Toner and
IPI SilverLock for this purpose. Toners and procedures were tested
according to the ANSI/NAPM IT9.15-1993 standard (The Effectiveness
of Chemical Conversion of Silver Images against Oxidation - Methods
for Measuring). We found that the Kodak Rapid Selenium Toner gave
very unpredictable results. The same recipe reacted very differently
with different products. This was true for both prints and films.
The other two sulfiding products gave very consistent results with
different products and showed an excellent ability to protect prints
and films against oxidation. For prints the Kodak Rapid Selenium
Toner was however preferred due to the image hue it created.

Further tests demonstrated that Ilford Mulitgrade RC-papers should
be treated in a solution of one part of Kodak Rapid Selenium Toner
to three parts of water at 20 C for 5 minutes and then rinsed for 5
minutes. One gallon of working solution will treat 200 20x25 cm
RC-prints so that they will meet the criteria in the ANSI/NAPM
IT9.15-standard. Less concentrated solutions will provide inadequate
protection. Both the laboratory testing and practical experience
confirms this.

Our standard procedure includes selenium treatment of all processed
RC prints. Continuous quality control of all toner treated batches of
print papers is carried out according to the ANSI/NAPM
IT9.15-standard to secure the highest archival standard for
RC-prints. However, for maximum permanence of photographic prints
for exhibitions we recommend fiber-based paper including selenium or
sulfur treatment.

Our results and recommendations for different products are published
in:

    Jesper Stub Johnsen and Karen Brynjolf Pedersen: "Comparison of
    Selenium and Sulfur Treatment for Protecting Photographic Silver
    against Oxidation" in: Nordic Conservation Congress, Copenhagen,
    Denmark 1994-99-111.

    Jesper Stub Johnsen: "Archival processing of black-and-white
    photographs as preventive conservation". In: Preprints, 8.
    International IADA Congress, Tubingen, 19-23 September 1995.

Jesper Stub Johnsen
Photographic Conservator
The National Museum of Denmark
Conservation Department

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                  Conservation DistList Instance 11:29
               Distributed: Thursday, September 25, 1997
                       Message Id: cdl-11-29-009
                                  ***