I don't appear here often (for which you may be profoundly grateful) but I
think I know what Woolstitcher means by 'runs'. When the SM needle is
burred or too large, it may hit a thread in woven silk and pull it - giving
the appearance of a run. An old trick for preventing puckered seams is:
before pressing - firmly hold the seam at the top and sort of slide the
joined fabrics down the threads of the seam. This will smooth out the
puckers - or at least give you a better chance when pressing. Polly Esther