Don't you hate it when your turpenoid tips over and spills or your medium leaks in your supply bag? Do you ever have a heck of time getting the top off gesso, linseed oil, or liquin because they cake around the top and get stuck?
To keep that from happening cut a piece of a plastic grocery bag (plastic wrap is too thin, but can be used if that's all that is available) at least an inch larger than the opening and place it over the top of the bottle or container. Screw the top back on as normal.
Note: This also works great with shampoos, lotions and other bottled liquids when you are traveling.
Take the top off -
place plastic over opening
|Screw top on over plastic...|
|tada... no more spills!|