If folks want to try what I do here are some more tips.
Goodwill on their 50% off days, usually Friday, are great for buying the sweaters. Men's large give you the most to work with of course but some small ladies and even children give you lovely, lovely soft lambswool in fabulous vibrant or pastel colours. The men's colours tend to be more drab. So much for peacocks.
Some directions tell you to cut the sweater apart at the seams in order to give the pieces a better wash and chance to shrink evenly. But I don't. I find I often use the sweater seam as a mitten seam.
Turn the sweaters inside out when you wash. Too much agitation will blur some of the more subtle patterns.
Watch for sweaters that have identical patterns at the cuff and the body. You will have more matching opportunities that way. Not all sweaters have identical patterns on cuff and body.
Felting removes a good deal of stretch from the sweaters. I find that even though I use a body or sleeve cuff as the cuff part of my mitten it will not hold onto the wrist. I sew a small elastic around the wrist. Be sure to use one with a soft feel. Attach while mitt is still flat, before final seam.
Since I match my patterns I hand baste all my seams before stitching on the machine with a stretch stitch. Much more time consuming but I like exact matches.
I find the thumb on my pattern is too narrow for all but the most lightweight wool. I make it wider.
Hope this does not detract from the fun. The mittens are great to give as gifts, use for fund raisers or to donate to homeless shelters.