what technique did winslow homer use
Although the drawings did not get much attention at the time, they mark Homer’s expanding skills from illustrator to painter. Like with his urban scenes, Homer also illustrated women during wartime, and showed the effects of the war on the home front. The war work was dangerous and exhausting. Back at his studio, Homer would regain his strength and re-focus his artistic vision. He set to work on a series of war-related paintings based on his sketches, among them Sharpshooter on Picket Duty (1862), Home, Sweet Home (1863), and Prisoners from the Front (1866).  He exhibited paintings of these subjects every year at the National Academy of Design from 1863 to 1866.  Home, Sweet Home was shown at the National Academy to particular critical acclaim; it was quickly sold and the artist was consequently elected an Associate Academician, then a full Academician in 1865.  During this time, he also continued to sell his illustrations to periodicals such as Our Young Folks and Frank Leslie’s Chimney Corner. 
Largely self-taught, Homer began his career working as a commercial illustrator.  He subsequently took up oil painting and produced major studio works characterized by the weight and density he exploited from the medium. He also worked extensively in watercolor, creating a fluid and prolific oeuvre, primarily chronicling his working vacations.  
Figure with Red Drapery by John Singer Sargent, watercolor
Hopper typically painted his watercolors on location. For him, capturing the uniqueness of a particular day was his true subject. In The Mansard Roof he played down individual features on the building so the weather, the time of year, the wind, the light and shadow, the movement of the awnings, and the play of warm and cool light dominated the scene.
Homer was born into an old New England family. When he was six, the family moved to Cambridge, Massachusetts, then a rural village, where he enjoyed a happy country childhood. His artistic inclinations were encouraged by his mother, an amateur painter. When he was 19, he was apprenticed to the lithographic firm of John Bufford in Boston. At first most of his work involved copying the designs of other artists, but within a few years he was submitting his own drawings for publication in such periodicals as Ballou’s Pictorial and Harper’s Weekly. In 1859 Homer moved from Boston to New York City to begin a career as a freelance illustrator. The following year he exhibited his first paintings at the National Academy of Design.
With the outbreak of the American Civil War, Homer made drawings at the front for Harper’s, but, unlike most artist-correspondents, he dealt more often with views of everyday camp life than with scenes of battle. As the war dragged on, he concentrated increasingly on painting. In 1865 he was elected to the National Academy of Design. Admirably capturing the dominant national mood of reconciliation, his Prisoners from the Front (1866) was warmly received when exhibited at the academy shortly after the war ended.
One of America’s most famous painters, Homer had a unique talent for portraying nature in a way that convincingly reflected the American pioneering spirit. Self-taught in both watercolour and oil painting, and a master of book illustration although he is best known for his seascape art, typically infused with strong narrative content. He also completed many fine landscapes and genre-paintings.
Homer’s Sea Paintings
“I prefer every time a picture composed and painted outdoors. The thing is done without your knowing it.”
Homer’s colorful watercolor painting below features a pleasing contrast between oranges and blues (complementary colors). I am not sure how Homer painted this, but I assume he started with general washes then scumbled color over the top. Homer also used black to draw your attention to the boat in the middle.