Round brushes are useful for fine lines and are versatile for both oils and watercolors, sketching, outlining, detailed work, controlled washes, filling in small areas. creates thin to thick lines - thin at the tip, becoming wider the more it's pressed down. They are used with thinned paint rather than thick paint. They are ideal for painting sash windows or cutting in or round curved objects with any type of paint, its long handle means easier control during use.