What technique did egyptian artists use to paint their relief carvings?

polychrome

Explanation:

Polychrome is the art of painting or decorating with many colors bidimensional works as well as certain parts of tridimensional works. It can relate to the practice of decorating architectural elements, sculptures, reliefs, etc., in a variety of colors.

your word would be isle.

isle is an island or peninsula especially a small one.

if you add the letter "a" you get aisle, which is a passage between 2 rows of something like chairs, shelves, or something else.