Re: Kallitype archivality -Reply -Reply

Bas van Velzen (eland@knoware.nl)
Thu, 2 May 1996 10:07:16 +0100

>On Tue, 30 Apr 1996, Kevin Won wrote:
>
>> My Kallitypes that show degration to the edges were made the same time as
>> others that don't show the same image degration. The ones that do show
>> bleaching from the edges are *very* bleached to 1 cm. I suspect that it
>> somehow got very contaminated. But these images were processed identical to
>> others which show no degration whatsoever, leading me to the belief that
>> *all* the images were processed correctly, with good chemestry (fresh
>> ferric oxilate), but some of them were subsequently contaminated
>> post-process. I don't recall any major contamination of any of these
>
>I get the impression that the degradation is rather even in a sort of
>ribbon around the edge -- if so, it's very unlikely to be something
>picked up from a drymount press, which would be in blotches and blobs.
>When you see a more-or-less even edge-disintegration on old photos it
>tends to be from the mat or frame -- bad materials, or moisture, or
>something of that order. Or I guess I should add, since I am not a
>conservation maven -- that's always been my assumption....
>
>Judy

Most degradation reactions need water (as liquid or as vapour)
and/or oxigen. Water is present in paper in two forms: as chemically bound
water directly bonded to the cellulose fibers and as water ON the fibers.
The amount of "loose" water changes with the air humidity. It is this
changing of humidity (by actual changes in relative humidity or, more
important, changes in temperature) that "supports" degradation reactions.
The water moves in and out of the paper, this water-movement can be
regarded as energy: energy = degradation (this is not totally correct but I
try to keep it simple). Without these changes the rate of deterioration
slows down dramatically. This is the reason that museums, archives etc. try
to keep the climate in their storage rooms as constant as possible.
Most paper is stored in piles, packs (a book!) or between other
materials. Because of the closed stucture of these piles etc. the largest
exchange of moisture is at the edges of the paper since the water can
travel freely from there in and out of the air. At the edges oxigen is
present in larger quantities and is "replenished" more by ventilation
(wanted or unwanted) than in the interior of the pile. Everybody has
noticed that pages of books turn brown at their edges before the rest of
the paper (if at all), this is why.
Bad materials in contact with paper can also deteriorate paper or
trigger deterioration: mats and backboards are notorious for this (unless
well made of course). So edge-disintegration is most times caused by the
way photos are kept and not necessarily by incorrect processing,
although....

Bas van Velzen

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