Wendy explains–
“–Ampex introduced another even higher output oxide, with a newly formulated binder as well, that exacted a deadly curse upon all who used it. Of course it wasn’t realized at first, it took a few years. The new binder was no longer the stable, inert formulation it had been. The supplier of the new batches had inadvertently allowed many short molecules, much shorter than before, to dominate the mix. These are very hygroscopic molecules, which simply means they absorb water readily, right out of the air.

The water causes a change in the state of the binder — it becomes a semi-liquid, and migrates from behind and in between the oxide particles, gluing them together and to the backing, up to the front oxide surface, where in its softened state it acts as a pretty effective glue, sticking to heads, guides, leader tape, fingers, rat hairs and floor sweeping… all the things you don’t want attached to your magnetic tape surfaces, which ought be smooth, dry, clean, and slippery!”