A couple years ago I did some tests where I photographed a light gray card on a dark gray card on various films ,stand developed in Rodinal 1:200 90m 68F and made a 10x enlargement of the edge. Some films showed a noticeable light line about 1mm wide on the print on the gray side at the edge with the black.These films were: Tri-X, HP5, Plus-X, Adox/Efke 100, Adox/Efke 25. A second group of films showed little or very little light line, they were more even. These were: T-Max 100, Delta 100, Acros, Delta 400, Pan-F, FP4. Is it possible that the emulsions in the second group may contain some even-ness additive or is there some other explanation?This information may be proprietary but comment appreciated, thanks.