I think I'm finding that the developer makes a difference, too. I'll be more sure of that after a couple more runs of tests. My results this week are up here: http://dwrphotos.com/blog/EmulsionResearch.htm#Current and one date back (Oct 30 - Nov 3)
I'm with PE in encouraging more folks to work on this. I just finished reading "Memoirs of a Photochemist", by Fritz Wentzel, and I was struck by how the past and future keep circling around each other. In many ways, APUG'ers are recreating the excitement and investigative energy of those early photographers. So much knowledge has been lost and even small machine shops and mechanical skills are getting harder to access. We're pioneers and historians at the same time. Very cool.