[pure-silver] Re: b&w print has discolored - selenium toning RC
- From: Richard Knoppow <dickburk@xxxxxxxxxxxxx>
- To: pure-silver@xxxxxxxxxxxxx
- Date: Thu, 27 Mar 2008 07:48:52 -0700
At 05:25 AM 3/27/2008, you wrote:
On Mar 27, 2008, at 4:48 AM, Tim Rudman wrote:
However, you say you didn't selenium tone the print because it was
RC. Why?
You will still give protection with selenium , (or polysulphide or
gold)
with RC papers. It doesn't have to be used only with FB.
Tim
I didn't know there would be any affect, toning resin coated paper.
Thank you! And I didn't know it gave any kind of protection. I
thought it was just for sort of a color change.
Janet
There is really very little difference between RC and fiber
paper. The emulsions are for practical purposes the same.
The support of RC paper is coated on both sides with a
plastic (that's the resin) so that its waterproof. In this way it
behaves more like film. Fiber paper is unprotected by any coating.
The disadvantage of fiber is that it absorbs the processing solutions
which must be subsequently washed out. For the emulsion washing is
pretty much by diffusion. The rate of a diffusion process is mostly
controlled by the difference in concentration of the ions to be
washed out in one side versus the other. So, for instance, the hypo
left in the emulsion after fixing leaves pretty rapidly when fresh
water is used for washing. The paper support, OTOH, washes out only
partly by diffusion. some of the hypo gets trapped in the fibrous
structure of the paper and moves out very slowly even when a wash aid
is used. For protected support, meaning RC, the support does not
absorb anything and washing time is whatever is sufficient for the
emulsion. Most RC papers will wash out to "archival" levels in about
4 to 5 minutes in running water. A double-weight fiber print will
take about two hours for the same level to be reached. When a wash
aid is used the wash time for fiber can be reduced to about 20
minutes but RC washes out so quickly that a wash aid is not
recommended with it.
Note that the emulsions of printing paper are quite thin
because the light must pass through it twice, so, relatively high
reflection densities can be obtained with a relatively thin layer of silver.
The effect of toning is exactly the same with both kinds of
support. Toning helps prevent chemical reaction of the image with
air-borne pollutants and those in mounting materials. The toners
which have been found effective in image preservation are those that
cause conversion if the image silver to silver sulfide, silver
selenide, or plate the silver with gold. The sulfiding toners are
those usually called Sepia toners although Sepia is actually the name
of a color. Gold toners have fallen out of wide use because of the
cost of the gold chloride, however, they are very effective preservatives.
It is also possible to get some degree of image protection by
other means such as the material in Agfa Sistan or Fuji Ag-Guard.
These are NOT as effective as proper toning but do not change the
appearance of the image.
Any print which is to be displayed should be toned. In the past
the recommendation was to tone using a 1:19 solution of Kodak Rapid
Selenium Toner. This toning was applied to microfilm successfully for
many years but about fifteen years ago it was discovered that film
treated with it was showing signs of image oxidation. Research by the
IPI determined that the toner was no longer working as it had in the
past. Selenium tends to tone high densities before low densities so
it was leaving some parts of the microfilm unprotected. The IPI
determined that the use of a polysulfide toner would tone evenly and
could be used for partial toning with complete image protection.
Selenium toner WILL provide complete image protection if toning is
carried out far enough. The recommendation of Dr. Nishimura, of IPI,
is to tone prints in a dilution of no greater than 1:9 for a period
of not less than 3 minutes at room temperature. The disadvantage of
this toning is that it will affect image color and density. The idea
of the high dilution was that it had minimal effect on the image appearance.
Kodak Brown Toner is a polysulfide toner which is effective as
an image protector when partial toning is used. For microfilm the
criterion is a minimum of 60% conversion of the silver as measured by
densitometric methods but for printing paper adequate protection is
probably had with any visible change in the appearance of the image.
In the past RC paper has suffered from short life due to the
evolution of peroxides from the material used to produce the highly
reflective surface under the emulsion. This is a different material
than is used for fiber paper. The effect of the peroxides was to
attack the image and the upper layer of plastic causing it to flake.
This problem was cured by adding anti-oxidants and oxygen scavengers
to the coatings. These are such as to be self-regenerating so they
should last the life of the paper. However, they can not protect the
image against the effects of residual processing chemicals or the
presence of insoluble fixer reaction products.
To be reasonably permanent any paper or film must be completely
fixed so that all of the unused halides are converted to a soluble
form, and must be adequately washed so as to remove these materials
and the bulk of the hypo.
Because well washed film and prints are susceptible to attack
by oxidizing agents in the atmosphere they should be toned,
especially if they are to be displayed or kept under uncontrolled conditions.
Full toning in any sulfiding toner or in selenium or gold
toner provides a very high degree of protection and, hence,
permanence. However, it does result in a change in appearance, this
seems to be unavoidable. Probably the least noticeable difference
will be made by using partial toning in a polysufide toner (KBT OR
T-8) or by toning in a gold toner.
Gold toners tend to produce a blue shift in image color which
may be more acceptable for some prints. Like selenium toner it does
not shift the color of neutral or cold tone papers much but can
intensify them slightly. As mentioned above the main drawback of gold
toner is the cost of the gold.
Note that the metallic substitution toners like iron-blue or
copper toners result in _lower_ image stability than plain silver so
should never be used for image protection.
--
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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