http://fineartamerica.com/featured/drape-study-i-joanne-hopper.html
or this example of soft edges in color:
or this one:
or this one:
from: http://emptyeasel.com/2007/03/28/realism-in-art-oil-paintings-by-james-neil-hollingsworth/
My point is there is no hard & fast rule for hard or soft edges: it depends on the nature of lighting, texture of the object, etc. Generally, cast shadows create hard edges, ambient and reflected light soft edges, etc. Use your edges plastically to make convincing drapery folds.
artists you may not be familiar with notable painting styles:
American artists:
John Copley (1738), Benjamin West (1738), Gilbert Stuart (1755), J. Sargent (1856), T. Eakins (1844), JK. Currin (1962), J. Schnabel (1951), E. Fischl (1948),
Women artists:
A. Gentileschi (1593), A. Kauffmann (1741), E. V-Le Brun (1755), C. Charpeniter (1767), J. Leyster (1609), J. Saville (1970), D. Tanning (1910)