Matched, paired, "quill" or "slip" wings are made by cutting sections of feather from matched opposing wing feathers, ( or sometimes from tail feathers). Usually primaries or secondaries, using a technique known as "pinch looping". It requires a little practice to do this properly. Such wings may be "set" or "bent" in a number of ways, to achieve various effects. Here are various slip winged flies, http://www.wildfisher.co.uk/smf/index.php?topic=16934.msg181108#msg181108 (http://www.wildfisher.co.uk/smf/index.php?topic=16934.msg181108#msg181108) these may also be dressed "advanced" or "set up forward" etc
These are matched mallard primary quills;
(http://img510.imageshack.us/img510/7087/duckquills.gif) (http://imageshack.us/photo/my-images/510/duckquills.gif/)
Selected slips cut out;
(http://img526.imageshack.us/img526/2523/wingslips.gif) (http://imageshack.us/photo/my-images/526/wingslips.gif/)
Slips placed together:
(http://img811.imageshack.us/img811/4379/wingstogether.gif) (http://imageshack.us/photo/my-images/811/wingstogether.gif/)
Placed on hook and tied in;
(http://img853.imageshack.us/img853/2523/pinchedloop.gif) (http://imageshack.us/photo/my-images/853/pinchedloop.gif/)
Mallard primaries are too coarse for most small flies, but they are good feathers to practice with.