What about moldy looking VHS tapes?
Mold on VHS tape - or what is it?
Evident crystal-like white powder looks like mold at first glance. In realty it is a chemical reaction that happens as the VHS tape slowly breaks down.
A tape that looks like this will not play back in your deck for very long. Soon enough, the fine, flaky powder will cover the inside of your VHS deck, and the VHS deck head which reads the tape will stop producing a clean image. You will start to see more and more dropouts, as that powder continues to build up on the head.
Inside look -- close up of powder build-up caused by older degrading tapes
VHS drum head cylinder which reads the tape
Eventually, the deck will need to be sent out for cleaning, because those long cotton swabs dipped in rubbing alcohol will only work as a "quick fix" for so long.
The tapes below required a special hand-cleaning treatment before being transferred. First, the tape case is disassembled then carefully cleaned.
Opened VHS tape is ready for cleaning
The activity happens in a protected environment.
Cleaning machine is used in a protected environment. Paper tape rolls continually get renewed as tape is cleaned.