The figure given in the crafting window is 5%, which is one in twenty. I have no experience to suggest that this figure is seriously off, but I haven't actually recorded the results of the thousands of crafts that would be required to test it.
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Remembering Tyneetryk
Phaedreas Tears - 15 years old and first(*) of true neutral guilds in Atys.
(*) This statement is contested, but we are certainly the longest lasting.
<clowns | me & you | jokers>