Encyclopaedia WoT: Said

Pronunciation: seye-DAHR, seye-DEEN

Saidar is the female half of the True Source and saidin is the male half of the True Source. Only a man can draw on saidin, only a woman on saidar. Saidin is fouled by the taint of the Dark One, like a thin slick of rancid oil on water. The water is still pure, but it cannot be touched without touching the foulness. (TEotW,Ch12) Their bonds, oaths and ties to the Great Lord protect the male Forsaken from the taint. (TFoH,Prologue)

References (Possible Spoilers)#

Tor Website Q&A - There are weaves that a woman can use to detect the resonance of the residue of saidin. The weaves do not detect saidin weaves directly.
In The Eye of the World
- TEotW,Ch16 - Touching saidar gives some protection from minions of the Dark One. Touching saidin sometimes gives protection and sometimes makes one more vulnerable.
In Crossroads of Twilight
- CoT,Ch23 - The Aes Sedai with bonded Asha'man report that saidin feels cleaner, but it is hard to tell if the taint is truly gone because saidin is always such chaos.
- CoT,Ch19 - Nisain reports traces of an unknown weave where Shadar Logoth stood. There was far more saidin used than saidar.
- CoT,Ch20 - Nisao reports that Anaiya and Setagana are dead. She tested for resonance and determined that they were killed with saidin.
- CoT,Ch30 - Nisao reports that Kairen Stang is dead, her neck broken with saidin.