UV filter question

I just aquired some very old lens shades that contain a piece of apparently
clear glass (not a diopter). They can't date any later than 1940. Were UV
filters available as early as the late 1930s?
Thank you

wrote:
I just aquired some very old lens shades that contain a piece of apparently
clear glass (not a diopter). They can't date any later than 1940. Were UV
filters available as early as the late 1930s?
Thank you

Yes. My 1935 Leica Manual mentions UV filters "to be used
only in high altitudes, mountains etc."

UV filters became more popular after the advent of
Kodachrome and Agfacolor because the early colour
films did not have an effective UV blocking layer
as today's films do and excess UV could show up
as blue on a colour slide. Most of the time with
B&W films a yellow filter is more desirable than
a clear UV filter.

In my 1943 Kodak Reference Handbook, the Wratten #1
filter is called "the Kodachrome Haze Filter."

Peter.
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