Digital BW, The Print

Richard Smallfield wrote:
> Hi,
> yes I recall that thread - it was Wilhelm's comment that was interesting.
> 
> Richard

Wilhelm's comment should be seen in the context of the early
1970's when analogue RC paper was introduced.
The RC (Polyethylene) barrier directly behind the emulsion
layer hardened and cracked in a reaction with the rutile
TiO2 whitener that was mixed in., releasing more oxidants in
the process. The photochemical process is roughly UV light 
bombarding TiO2, releasing peroxides that harden and crack 
the polyethylene and allow peroxides to attack the image..

Meanwhile a lot has been changed in the polymers available
for the barrier and in the whiteners to add to that mix.
Antioxidants are added and UV light reaching TiO2 is
reduced. Related to that: OBAs filter UV light out as long
as they are active. In theory any oxidising agent would
attack colorants, dye more than pigment but a modern RC
layer no longer releases peroxides to that degree. With UV
light available it is more likely that the colorants will
bleach due to the UV than to the possibly released
peroxides. The Ozone tests done by  Image Engineering for
ColorFoto made it clear that colorants are better protected
to ozone in RC papers than on non-RC papers. Possibly
because the RC layer blocks ozone coming through the paper
base but more likely the anti-oxidants mixed in neutralise
the ozone. Carbon pigment particles used in B&W inks are
more or less inert to influences described here.

With the Vivera pigment and HP RC paper, two components of
aging are estimated to be around 70 years: ozone fading of
the pigments and the RC barrier falling apart. The
lightfading resistance is 80 - 105 years. HM's PhotoRag
however will show ozone fading of pigment between 50-60
years for the same ink in bare exposure, the lightfading
resistance is more than 115 years.  So for bare exposure the
RC paper may be a better choice than the Photorag. Maybe it
is bad taste to suggest plastic as a carrier of art, I know.
Cotton, fiber, baryte and gelatine suggest quality for much
longer .........

http://digitalkamera.image-engineering.de/downloads/Haltbarkeit_Papiere-Cofo.pdf
bottom of page

Wilhelm's ozone testing looks like being less severe than 
Image Engineering's test, Wilhelm labelled a lot of ozone 
tests in the past as being "still in test" while the recent 
tests (Harman Fibers, Photorag, Epson Exhibition) right now 
all show a >100 years label. For the Fiber papers I like to 
see an Image Engineering Ozone test to get some perspective 
of their ozone resistance.

Part of that was discussed in the old threads or at least
links to articles on that subject were there

-- 
Met vriendelijke groeten, Ernst


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