Double cross stitch is a simple variation of the cross stitch. Two layers of cross stitches are layered one on top of the other. This can be a border stitch or a filling stitch. It grows very fast so it can be used to fill large spaces with embroidery. It can also be used to create two tone checkered pattern like shown below.
Start with diagonal stitch, also called a half cross stitch like shown below.
Complete the cross stitch by stitching an intersecting diagonal stitch.
Now stitch a horizontal stitch like shown below.
And another vertical stitch.
Two tone filling stitch.