Reading all of chapter VII is very informative about sensitizing emulsions. Methyl Violet has an absorbance spectrum very close to ethyl violet and chemically the two dyes only vary by substituting methyl groups for ethyl groups.
Thank you very much for your kind help Falotico. I will try Methyl violet with suggested 50% alcohol. Now how to mix 1:20 000 is an another feat... :0)