@mijostyn,
This was likely the last (and best?) patent that RCA filed for vinyl record composition - https://patents.google.com/patent/US3960790A/en, this is the patent download - https://patentimages.storage.googleapis.com/b6/ac/a3/33b9d37bfdc952/US3960790.pdf. Its worth reading - its actually a short read - but addresses what happens if the composition is not right.
PS/Not sure if this was the intent - but you may have accidently questioned the value of you conductive brush - but, your testing during winter may show very different results. In the meantime, I use a UV light for cleanliness inspection (10Watt, very short exposure), and its amazing on the variability of the vinyl composition - the best virgin is uniform in color, while the repressed or lower quality can be a kaleidoscope of fluorescent colors.
This was likely the last (and best?) patent that RCA filed for vinyl record composition - https://patents.google.com/patent/US3960790A/en, this is the patent download - https://patentimages.storage.googleapis.com/b6/ac/a3/33b9d37bfdc952/US3960790.pdf. Its worth reading - its actually a short read - but addresses what happens if the composition is not right.
PS/Not sure if this was the intent - but you may have accidently questioned the value of you conductive brush - but, your testing during winter may show very different results. In the meantime, I use a UV light for cleanliness inspection (10Watt, very short exposure), and its amazing on the variability of the vinyl composition - the best virgin is uniform in color, while the repressed or lower quality can be a kaleidoscope of fluorescent colors.