Re: Cooking in glass mounted slide

[P3D emdesher <emdesher@xxxxxxxxxxxxxxxxxxxx>]

On Wed, 4 Dec 1996, P3D Cliff Howard wrote:
> 
> The following is a quote from "The Source Book,
> Kodak Ektagraphic Slide Projectors"
> 
> Transparency Life
> 
> "In general, transparencies kept in open-frame mounts
> can be expected to last longer than those kept in glass
> mounts. A transparency mounted in glass has a thin
> insulating layer of air between it and the glass, and the
> heat from the projection lamp must be transmitted
> through the layer of air on each side of the
> transparency, and then through the glass. The
> transparency will get hotter before the temperature
> stabilizes than will a similar transparency in an
> open-frame mount. With an open-frame mount, the
> heat is carried away by air moving over the
> transparency surface."
> 
> Sounds like the same principle that's used in double pane windows.
> 
> Cliff Howard
> 
> 
Did this Kodak publication indicate how the slide was bound?  Was the glass
sealed with tape?  In the Kodak customer service pamphlet AE-36, a 
balanced discussion of mounting with or without glass gives the advantages 
and disadvantages for both methods.  If protection from scratches and 
damage is needed, they say "A scratched slide is a ruined slide.  So 
don't take chances with your valuable slides-protect them with glass." 
If you handle your slides carefully, they give a technique for glassing a 
slide on one side only.  This is to flatten the film for projection 
purposes, similar in intent to one-sided glass RBT mounts.  Furthermore,
"Popping (often called focus shift) occurs with cardboard-mounted slides 
when heat from the projector dries the film, snapping it into a slightly 
concave, or dished, shape and requires refocussing of the projector."
Whether to mount with or without glass depends on number of factors, 
and any method involves trade-offs.  To choose the "best way" depends on 
how you project or view your slides, how often, and how the slides are 
stored and handled.  Dennis Sherwood


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