Platine can be very stubborn to clear, but after following some advice from
David Fokos, scrutinizing commentary on the list, and a little experimenting on
my own, I've found a system that works: following the potassium oxalate
developer, rinse the print with constant agitation for about one minute in a
warm (110 to 120 degree) running water bath. I then clear using full strength
Hypoclear at the same warm temperature, again with constant agitation. I've
been using a Jobo processor for the three clearing baths. Though not everyone
has a rotary processor, it makes the process much more predictable due to the
ease of temperature control and agitation speed, without damage to the paper
due to handling. The constant agitation seems to be the trick (or one of the
tricks) in clearing Platine.
I use the same contrast agent as you, and don't think that's part of the
clearing problem. Platine behaves the same in the clearing baths with or
without the contrast agent. In a perfect world, I wouldn't need a contrast
agent, but not all my negatives are as exquisitely formed as I would like.
Good luck with the spots. They really do sound like undissolved crystals- of
some sort.
Tom Hawkins