I was readng Mees 'From Glass Plates to Ektachome' on the weekend (Thanks for the loan, David William White), and there is a chapter on sensitizing dyes.
There is a reference to a paper that Mees published in some scholarly journal in 1920 about the absorptive propoerties of many dyes of interest for photo sensitising.
The organic chemistry discussions on thier synthesis flies miles over my head though.
Chis - I have packed 6 small plastic bottles of different dyes and a number of nose and mouth surgical masks in a bubble envelope; all that remains is to get to a postal outlet for the customs declaration label and postage.
One of the things I tried to send you was an effectve yellow. Apparently yellow is not a popular biological stain, because I have lots of outher colurs, but short on yellow. The actual yellow I had is closer to orange, but there is a red dye included that is an indicator as well, and at moderate pH in my tap water is very yellow.
I hope you have fun playing when you get these. Be warned that from my past experience with shipping to/from the midwest US from where I am there seems to be postal black hole that makes packages take 6 weeks.