Glossy labels vs matt labels - and the "frosted tape" is 3M's magic mending tape - it has a matt top surface.
I've resorted to this fix when dealing with optical problems and overly reflective surfaces in the past, along with using Tippex (liquid paper) to narrow the viewing window on an optical sensor so that the chopper wheel it was shining through could work - the manufacturer one had a narrow window compared to the replacement unit, slots in the chopper were wide enough to allow light pulses through that were long/smeary enough to screw up a centrifuge as it hit 15,000 RPM on the way up to 45,000 - resulting in emergency shutdown being invoked. You really _don't_ want that to happen often. Closing up the optical viewing window solved the problem and got nice clean pulses at silly high speeds
Biting the hand that feeds IT
