The WW1 gas hoods had lenses not made of glass but some form of transparent material possibly mica which lost transparency over time which is one reason why I suggested this source
Scotlands People don't have any records for COWAU , ( 0 counts in 0 categories ) There were two Alexander Cowans , 1 dow in scicily 1943 aged 27 ,and the other NWE K.i.a 1945 aged 26.
My friend is under the impression that his father hid this man for a while and then he was moved on by others.