I made thumb gusset: I increased every other row 2 stitches so that at first there were 2 stitches between them, then 4, then 6 and so on until there were 18 stitches for thumb. I put thumb stitches on the left yarn waiting and casted on 2 stitches in their place.

These mittens are so beautiful. Just a pity that they are little too big for me. I think that I should knit some mittens uder them that I could use these.