To pass on transient impressions, light and colour nuances, artists have to go out of their workshops to the open air. But until the middle of the XIX century it was difficult to go out with oil paints which were stored in bags made of pigs' bladders.
To squeeze paint to a palette, one had to pierce a thin wall of the bag and then repair the hole. It was only in 1842 that American portrait artist John Goff Rand invented durable tin tubes for oil paints. Perhaps, the mankind would not have heard the names of famous French impressionists for a much longer time if portable painter's case with such paints had not appeared.