55% should be ok.
As far as glycerine/sugar, one may be redundant. This is one of those
things that requires a lot of repeated testing. You may think you changed
one variable only but other factors may come into play.
>pigmented/gelatin solution and was wondering if perhaps the former might
>not contribute to the problem. I may have also caused the
>problem by leaving the coated tissues on drying racks for several
>days before putting them away.
You're looking for trouble when you do that.
>In terms of Mylar itself, are there some varieties which are coated?
Many. Mylar is DuPont's brand name for polyester. They make over 60
different types, designed to accept printing ink, xerographic images, and
have properties like being anti-static, etc. Some years ago I obtained a
frosted/matte type to store sheet film without the risk of sticking but the
material was just like fine sandpaper. I also experimented with the same
material as a temporary support to obtain double transfer monochrome
carbons, with mixed results.
The "neutral" grade, coating free is called Mylar "D"
Luis Nadeau
awef6t@mi.net
Fredericton, New Brunswick, Canada
http://www.primenet.com/~dbarto/lnadeau.html