[pure-silver] Re: FW: Re: What happend? CORRECTION
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Thu, 29 Jun 2006 11:17:09 -0700
----- Original Message -----
From: "Aaron Reece" <oboeaaron@xxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Thursday, June 29, 2006 5:21 AM
Subject: [pure-silver] Re: FW: Re: What happend? CORRECTION
I've been following this thread with interest. My next
question would
be, "What is the effect of re-fixing the print?"
Regards,
Aaron
On Jun 29, 2006, at 7:58 AM, Breukel, C. (HKG) wrote:
I also put some 1+9 KRST on the golden borwn coloured
area,
and sure enough: a bright red stained spot appeared
(which could be
wipped of easily), so it's inadequate fixing after all
Re-fixing or re-washing will not help once the image
begins to deteriorate. There are some treatments that can
make the image look better, i.e., remove the stain, however,
they have been shown to accelerate future deterioration of
the image. The only cure is to re-print.
Prints to be displayed should be toned. If a great change
in color or density is not wanted the best toner is Kodak
Brown Toner, which will provide a significant amount of
image protection with partial toning. If a greater change in
color and density is acceptable full toning in Kodak Rapid
Selenium Toner or a Gold toner is OK but neither provides
enough protection when only partial toning is accomplished.
Stabilizers like Agfa Sistan or Fuji Ag-Guard are also
effective but where no change in the appearance of the image
is acceptable but neither is as effective as toning.
The two mechanisms of image degradation are sulfiding and
oxidation. Sulfiding is mostly from incomplete fixing or
inadequate washing although it can be produced by
atmospheric polutants and impurities in mounting materials.
Oxidation is almost all from atmospheric polutants or from
mounting materials. Early RC paper had an oxidation problem
caused by gasses emmitted by the Titanium dioxide used in
the plastic underlying the image to make it highly
reflective. That problem has been eliminated in modern RC
papers by the use of scavengers in the coatings.
Curiously, oxidation is more serious for very well washed
images that are not toned. It was found some forty five
years ago that a very small residue of thiosulfate in the
emulsion provided a significant amount of protection against
oxidation of the silver image. The mechanism is probably the
generation of a layer of sulfide on the silver crystals.
This mechanism is far less effective than proper toning and
should not be relied on but does explain why the heroic
washing recommended for fiber base prints in the past is no
longer considered good practice.
Sources of oxidizers are prolific: gas stoves and
unvented heaters, high voltage devices producing Ozone (copy
machines, some TV sets, Ozone producing air "cleaners"),
fresh paint, some plastics, automobile exhaust, some types
of resinous wood, especially if fairly new, some others I've
forgotten. In any case sources are very common. Sulfiding
can be caused by polutants containing sulphur compounds.
These include burning of hydrocarbon fuels, especially coal,
but they are more common as impurities in mounting or
storage materials, particularly some types of paper or
cardboard.
There is a very great deal in the literature about this.
Some may be found at the Conservation On Line site at
http://palimpsest.stanford.edu. While much of the
literature there pertains to books and other print media
there is a substantial amount applying to photographic
materials.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
=============================================================================================================
To unsubscribe from this list, go to www.freelists.org and logon to your
account (the same e-mail address and password you set-up when you subscribed,)
and unsubscribe from there.
Other related posts:
