Spell Weaving is the meta-magic ability to give a sustainable spell the ability to remain for a limited amount of time after the magician has stopped sustaining them. The diffence between weaving and quickening is that weaving is a much more tenuous and fragile connection than a quickening since it has not been given any of mages lifeforce to help sustain it in the ever changing astral plane.
To weave a spell, the magician must first be able to astrally perceive. The weaving test is made using Sorcery (Spell Casting) (totem modifiers help) vs TN 6 or the spell's force (which ever is higher). The TN is modified by Damage Modifiers, Background count, and Astral static (but not the modifier for sustaining that spell). The weave will last for a number of turns equal to the weavers grade times the number of successes (grade x succ). The number of turns may be lessened if there are unwanted turns, but the weaving can not be later increased.
Centering can be used to help modify the test. Use the same TN as before, and every two successes gives one extra success for the duration (though one must still succeed in the actual weaving test before these can be counted).
In combat or against dispelling, woven spells will be at 1/2 force. Woven spells will react to grounding similarly to quickened spells (ie if you let grounding accour through quickened spells it will happen through a woven one, otherwise the connection is to tenuous to allow grounding occur).
Permanant spells can not be woven, neither can woven spells be later quickened, anchored or resustained. Woven spells can not be masked.
Walks-with-Milkbones (a grade 2 initiate) wants to turn into a Rottweiler for a short amount of time. Casting Shape Change he turns himself into a Rottweiler and sits down to meditate (his secondary centering skill - he would sing, but can't as a dog). He perceives the spell and goes about the process of weaving it into the existing mana flows. He gets very lucky, the mana flows here are a little better than normal, and gets two successes, combining that with his one effective success from centering (two successes = one success) Totaling everything he gets grade 2 x 3 successes = 6 turns of being a Rottweiler.