Which technique is used to embellish a base fabric with yarns?

The technique used to embellish a base fabric with yarns is embroidery. This method involves stitching patterns or designs onto the fabric, utilizing various thread types and stitching techniques, which can add texture, color, and intricate detail to the work. Embroidery can take many forms, including hand-stitching and machine embroidery, and it allows for a significant level of creativity in designs.

The other options do not specifically focus on the use of yarns for embellishment. Patching involves adding pieces of fabric onto a base fabric, which is typically used for repairs or decorative effects but does not inherently involve the use of yarn as a primary embellishing medium. Applique refers to applying smaller pieces of fabric onto a larger base fabric to create a design, which again does not primarily involve the use of yarns. Screen printing is a method of applying ink designs onto fabric and does not involve yarns or stitching techniques, making it distinctly different from embroidery.