P3D Re: Re: P3D Re: Prints vs slides - Archival Qualities

[roberts@xxxxxxxxxxxxxxxxx (John W Roberts)]

>Date: Wed, 19 Nov 1997 19:56:31 -0700
>From: "Dr. George A. Themelis" <DrT-3d@xxxxxxxxxxxxxxxxxxxxxxxxxxx>
>Subject: P3D Re: Prints vs slides -  Archival Qualities

>- Also in my collection I have black and white prints from less than 
>  100 years ago that have faded.  I mean almost totally gone.
 ...   
>- I think the original question was to compare color slides with color
>  prints.  Color prints of several decades ago are now fading.

Having attended an actual stereo club meeting and seen a great assortment
of slides, I appreciate stereo slides more than I did before, but I still
suspect that a heavy emphasis on slides tends to encourage a number of
mental "habits" that are not entirely appropriate:
 - There is a tendency to think of the physical stereo photo as a unique,
   hand-crafted item. That's not necessarily "bad" if the status quo in
   stereo is all a person ever wants, but ability to mass produce would be
   very useful in expanding use of 3D way beyond current levels. Both slides
   and prints can be mass produced on an industrial scale, but for the
   intermediate step of producing several dozen duplicates, an individual
   can readily have additional prints made from the negatives, at essentially
   the same image quality as the original. I've never tried to duplicate
   slides, but most of the discussion on this topic on P3D over the last few 
   years has been on how unsatisfactory the results are in comparison to
   the original. (Which may have been exaggerated - anyone care to express
   views on slide duplication? What type of film is used to take the
   originals for mass-produced View-Master slides?)
 - There is a tendency to think of the thing you view as the only record of
   the image - thus if the slide is damaged then the stereo view is forever
   damaged, and if the slide is lost then the stereo view is forever lost.
   Note that the discussion quoted above is on the durability of the *prints*.
   But if the print photographer is careful to keep the *negatives* safe, then
   at least in the near term, the stereo card can be re-created if
   necessary, and it's the archival properties of the *negative* (rather than
   the print) that's of the most interest in terms of continued existence of
   the image. (I don't know what the archival properties of color or B/W
   negatives are - that would be interesting to learn. I seem to recall that
   at least some Civil War negatives can still be used to make prints.)

It might be useful for those who mainly use slides for stereo to think about
ways in which the good features of prints can be applied to their medium
of choice. (Similarly, it would be nice to have a stereo "opaque projector"
for public viewing of Holmes cards. :-)

>- When a color slide is fading, does that mean that the colors are
>  shifting or the image strength is decreasing?  I am asking because 
>  I also have some old Ektachrome stereo slides in my collection that 
>  have shifted colors.  Some of them have turned red.  The image 
>  however is still strong.  If you do not care for color, you have not 
>  lost anything.

>- Some time ago you expressed faith that technology will be converting
>  flat pictures to stereo and urged us not to throw away our 3d pictures
>  just because they are 2d.  The same technology could be used to 
>  preserve images.  So, what difference does it make if our stereo slides 
>  will lose some color and strength 50 years from now?  By that time we 
>  should be able to scan them in very high resolution, intensify the 
>  colors and store them for ever.  

I don't know the mechanics of slide fading, but it's almost certain that
some "information" is being lost, in terms of precise gradation of the range
of "grayscales" (display terminology). So you might restore the photo of
Great-Great-Great Uncle Hubert to the proper color balance, but he might
appear to be wearing cheap theatrical make-up. If you're serious about long-
term preservation, it's probably better to digitize it *before* fading starts
(even if better digitization techniques are available in the future, the
*color* information from the earlier digitization can be used as a reference).

If you make a B/W copy of a color slide that has lost some colors but
retained others, the result would not be "panchromatic" - it would be
essentially equivalent to taking a B/W photo through color filters
(which isn't necessarily a *bad* thing - it just causes the appearance
to be different). (Paul Ivester posted on this topic.)

John R


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