Make your own pH indicator paper, or at least some dyes therefore:
http://antoine.frostburg.edu/chem/senese/101/acidbase/faq/household-indicators.s
html
Can't find a source for a color chart, though.

could someone give me some information as to which would be best way of
getting high definition using the conventional B/W photography negative, on
this project I'm about to undertake.
I will be taking photographs of clock dials and their numerals plus chapter