Wobbly, yet relatively smooth surface (like a fine sandpaper) that appears on the surface of the casting
Indicates that either the casting skin was destroyed by excessive shot blasting or the wax pattern was over-etched, giving it a wobbly surface
Causes of this defect are evident in the metal and other portions of the process; to cure, R&R recommends taking the following actions:
Variable depth of oxide formation on casting skin.
Reduce atmosphere, use carbon stucco or can molds.
Excessive shot blasting times.
Avoid excessive shot blasting times (knockout).