What caused this?

[EJC]

Hi Folks

This is a sun set photo converted to black and white. I tried to burn the mid tones in the sky along the upper right toward the middle using a big soft edge brush at 3%. It left a herring bone sort of pattern that wasn't in the clouds. Moving the brush at different speeds didn't make any difference. Any one out there think they know what happened?

Thanks
EJC