How does Alfred Tennyson, Baron Tennyson use imagery in Idylls of the King?

Imagery:

"'A doubtful throne is ice on summer seas. . . .'"

"Thereafter, when Sir Balin entered hall, / The Lost one Found was greeted as in Heaven / With joy that blazed itself in woodland wealth / Of leaf, and gayest garlandage of flowers, / Along the walls and down the board; they sat, / And cup clashed cup; they drank and some one sang, / Sweet-voiced, a song of welcome, whereupon / Their common shout in chorus, mounting, made / Those banners of twelve battles overhead / Stir, as they stirred of old, when Arthur's host / Proclaimed him Victor, and the day was won."