the term 'chalky paper' in connecton with silver originates
from the prewar period [192x-193x]. With modern stamp issues
you're dealing with coated paper vs uncoated paper, the material
used for coating the paper stamps are printed on may vary a lot.
Just have a good look at the stamp surface and you find it covered
or not, showing at times little cracks, speckles etc.
as to the reaction under UV-light, there may be no reaction [dull,
creme], a reflection [violet] or the reaction of a whitening agent
[that is in the coating, not in the paper mass, and the agent can
be of varying intensity], the reaction of a luminescent substance
put in there to be of assistance while sorting out covers [both
fluorescence and phosphorescence]. In the mean time the paper mass
has its reaction of its own.
After soaking most of the original luminescence may be gone, and
at the same time luminescence may have transmigrated from other
stamps or the covers they were on as well, so be careful...
Apart from all the aspects brought in, the term "chalky" is originally used by English collectors who refused to apply this term to coated stamp paper in the early days iof World War II as this paper did NOT react to silver....
So, this term "chalky" is comnpletely outdated and does not refer to coated paper vs uncoated paper. "Normal paper" has no meaning at all :)