I am not the most fastidious pot washer: over the years, my copper-bottomed fry pans have developed a layer of (I guess) burned oil residue.  Aside from any "ick" factor, does this affect the the performance of the pan? I've been trying to scrub a little bit off every time I wash them but when I have seen cooking shows, etc. I see pans that look like mine.  Does it matter? And if it does, is there a way to get this off aside from brute force with a ScotchBrite pad?   
Freezing fries opens up their texture and makes them more fluffy. This is helpful for regular fries or sweet potato fries.  Sweet potatoes have too much sugar and not enough starch to crisp up on their own. The only crispy sweet potato fries I have ever made- or eaten- were coated in starch to provide the crispiness.  While I haven't tried this exact recipe- I haven't used club soda for example- it has all the right steps and looks like it would work. 