For what it’s worth, from when we were Gepe:
1 - Sometimes it appears that the glasses, mostly on older mounts, have a grey coating. Why is this and how can I clean the glass?
The grey coating you see on the glass is probably calcium-carbonate crystals emerging from a chemical reaction between the carbon-dioxide (CO2) in the air and the Calcium (Ca) in the glass. This can sometimes be seen as a grey haze on the surface of the glass.
It is a phenomenon that occurs with all glass materials, from the finest wineglasses on the shelf at home to normal windowpanes. After a period of time a grey surface appears which naturally has to be washed off to become clean again.
This problem is known among all glass manufacturers and they are, of course, trying to find a permanent solution to it, but so far they have only managed to delay the reaction.
It is difficult to determine how long a period of time it is before this greyish surface occurs, however, it is important to store the slide mounts in stable conditions, preferably dry and at a constant temperature. However, these crystals are not dangerous or harmful to the slide film, as it remains on the glass and does not transfer to the film.
A recommended method of cleaning glass slide mounts is to use a liquid lens cleaner and a smooth lens cleaning cloth.
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