Old Shale Lace Pattern

Pattern
Cast on a multiple of 18 stitches.
Row 1 (RS): Knit.
Row 2 (WS): Knit.
Row 3: Purl.
Row 4: Knit.
Row 5: *[K2tog] 3 times, [Yo, K1] 6 times, [K2tog] 3 times; rep from *.
Row 6: Purl.
Row 7: *[K2tog] 3 times, [Yo, K1] 6 times, [K2tog] 3 times; rep from *.
Row 8: Purl.
Rep rows 1-8.