vetkilr - the wood foiling method is a way to prevent combustion of the wood.  I use the ramping method (1/2 hour at 130, followed by increasing to the set temp), but either way will work.  I know you're looking for an answer to appearance of the bark; this isn't it.  Foiling the wood, or slowly increasing the temp is only a means to prevent the wood from combusting.  If you've had a problem with the "smoke belch," or thick, grey smoke, then follow these methods.