Oct 11, 1960
Dear Dr. Lederberg,
Through a misunderstanding I did not get any reprints of my note in J.O.S.A. regarding the Hoshino-Yoshida filters, nor have I been able to get the original article.
I have not used the filters for several months.  I have noticed, however, that exposure to daylight has bleached them making them transparent to the visible.  I enclose a sample which was prepared at the time of my JOSA note.  Originally it was uniform over the entire surface.  It was stored between other filters which permitted it to be exposed more around the edges.
I dyed the polyvinyl alcohol films as soon as they were dry and hard enough to remove from the glass.  At this stage they are much more easily stretched.  If they are left for several days they become much harder.  I think it is quite possible that the properties of the filters might depend on the aging time before dying, or possibly they should be very thoroughly dried after dying
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and before exposure to any light.  I am sorry that I have not had the time to do more experimenting with them.  I do not know of any other work on these filters.
Please let me know if I can be of any further assistance.
Sincerely,
Myron Jeppesen