Second batch of LMM tracks on Rx film

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The next few attempts to record LMM tracks were hard to understand, with large hazy black blots along the sides of the films, as if daylight entered through the creases and folds of the bristol paper sheets. Under the microscope, these blots revealed numerous LMM tracks sunk in a dark fuzzy background that spread wherever the film was in contact with the bristol sheets; so the bristols were clearly contaminated with developer chemicals.

So I tested a new stack assembled as follows: positively charged alu sheet / new bristol / Rx film / new bristol / negatively charged alu sheet. That stack was sandwiched between the plexiglass and glass plates, and the whole thing was then wrapped in 6 layers of presumably opaque black plastic sheets.

Please note: The last picture is in false colors.

This second recording attempt (long: 52 hours!) was made under a voltage difference of 54 volts, followed by 5 minutes in the developer, 10 minutes in the fixer and a 20 minutes rinse.
Result: the film is quite clear and nearly empty at first glance, but the microscope reveals some faint tracks with these characteristics:

Conclusions: it seems that development duration was much too short (hence few tracks, most of them quite faint); furthermore the stronger electric field might explain the observed reduction in the amplitude of the tractor track patterns (that's to be checked).