I have been reading a book (no longer in print so I bought it used), "Techniques of the Impressionists" by Anthea Callen. In the beginning, she points out that paint was not originally available in tubes; it was kept in glass jars with cork or glass stoppers. This somewhat prevented artists from painting outside as paints were not portable.
So Windsor Newton invented paint in tubes. This allowed artists to pack up their oil paints (acrylics had not been invented) and paint out in the open as the Impressionist group often did. http://en.wikipedia.org/wiki/Plein_air I have taken paint in tubes and their portability completely for granted.
