tipp: I recently finished my Jaster Mereel (
http://www.thedentedhelmet.com/showthread.php?t=45259&p=656441&viewfull=1#post656441 ) and made the Cape last week ^^
i used a heavy Linen Cloth with a raw webbing to prevent flabbing too much around. Light cloths tend to do that ^^.
So For weathering i can suggest several methods.
1. Anglegrinder: Wrap it tight together and make some cuts with an motorized angle grinder - only peripheral
2. Pyroeffects: wrap the cape together including some fireworks ( careful)
3. Fire: nothing shows more signs of burnings.... than burnings

i dunked my cape in some Aceton and set it on fire for a second befor throwing it into a bucket.
4. hang it on the rearbumper of your car and take a drive though the woods
lesser dangerous methods:
1. appliyng a little haze of brown and black spaypaint to tone the cloth down
2. black shoewax or old fat ^^
the possibilities to **** something up are endless

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