I'm having a problem removing labels from various "liquor" bottles in my washing plant.
The medium of washing is hot water @ +/- 68 deg. C. with Caustic soda as the activator.
Some bottles have a plastic cover on the Labels that seem to prevent wetting, and are proving VERY DIFFICULT to remove. I have a wetting agent, plus a water softener added to the mix as well.
What "NATURAL" solvent, if any exists, can I use to overcome this "hiccup?"

Aceton is the basis for sticker solvents ! Try this link for the required information :

How to Remove a Sticker from Glass - wikiHow

:)

Yes, and exactly how many are you having to wash, I have set up special designed washing machines, in all sorts of plants to remove labels when there is high quanity.