Logan loves wearing his slippers so much that he wore holes in them, in spite of the double layered soles I knit before fulling them. I should have taken a photo of the holes before I started mending, but I had to intervene quickly with a ball of yarn before they got any worse!
At the toe, both layers had worn right through, so I darned a woven mend on both the inside and the outside, using matching wool. But where only the outside layer had worn away, filling in with chain stitch was the way to go.
Separating a length of the three-ply yarn into single strands gave me the perfect weight of matching wool with which to embroider.
First I removing the frayed edges, then worked snugly packed rows of chain stitch right onto the inner sole, without going through to the inside of the slipper. Since this embroidery is free-form, it is easy to fill the irregular space with a sturdy, smooth mend that will full with wear.
The question now is whether Logan will wear out the mends before he outgrows the slippers!