What major advancement allowed impressionist artists to paint outdoors more easily?

The development of oil paint in tubes was a significant advancement that greatly facilitated the ability of Impressionist artists to paint outdoors, a practice known as plein air painting. Before the introduction of tubes, artists typically had to prepare their paint by grinding pigments and mixing them with oil in a palette. This process was time-consuming and made it difficult to transport the materials necessary for painting outside of a studio setting.

With the advent of paint tubes in the mid-19th century, artists could easily carry pre-mixed oil paints wherever they went. This portability allowed them to respond more spontaneously to changing light and atmosphere, which were key interests for Impressionists. They could set up their easels in various outdoor locations, capturing the fleeting effects of sunlight, color, and movement directly from nature, rather than relying on sketches made in the field that were later completed in the studio.

The other options, while they might represent advancements in their own right, do not directly address the specific need for portability and convenience that the tube paint provided. Larger canvases would not have resolved issues of transport; new brush technologies may have improved technique but did not impact the ability to paint outdoors; and innovations in watercolor techniques, although relevant to painting, are not directly connected to the oil-based