A beautiful method of picking up stitches for a second fabric layer

Here is a beautiful method of picking up stitches on the inside of a stockinette fabric, so as to create a second, inner layer of fabric for facings or the like.

Step 1: run a column of reverse stockinette (ie: purls) where you want to start the new fabric.  You can either create this column of purls as-you-go, or insert it afterwards (possibly easier) by dropping a column and hooking it back up. When you flip the fabric over, this has created a single column of KNIT stitches on the reverse stockinette face of the fabric.

Step 1: on the reverse stockinette face of the fabric, you will have 
created a single column of knit stitches (darker green in illustration)

Step 2: insert a small crochet hook SIDEWAYS into each stitch of this column and draw through a loop

Step 2: Using a crochet hook, draw loops through the column of
knits as shown  

Step 3:  Deposit each loop as it is made onto a knitting needle (circular or double pointed). You will now have a line of stitches picked up on the inside of the garment which magically seem to grow right out of the row of knits.  You will not believe how completely and utterly invisible the pick up is--invisible from both sides of the fabric. (I've drawn it in pink here so you can see it, but when this is worked in the same color as the stockinette fabric, it disappears.)

Step 3: Each loop is deposited on a circular needle or dpn
as it is created.  Although the picked up stitches are shown
in a contrasting color for illustration purposes, if the same
 color is used, the pick-up line is perfectly invisible from
either side of the fabric.

Once your stitches are picked up, you simply knit away.

In the wool: the fabric to the right (at right angles to the line of knits)
was picked up through the line of knits and created as described in this post

This trick can be used for many purposes, but a really wonderful use is to make a little knit facing for a zipper.  The zipper tape lies inside, between the two layers of fabric, for a very tailored look.

A note on gauge--
Obviously, this method involves picking up one stitch for each row. Yet, this might make the fabric sag and gap, as row gauge is smaller than stitch gauge in knitting (more rows/in than sts/in).  This is solved by using a smaller needle and knitting tighter, to bring the st gauge of the facing in line with the row gauge of the garment.  If your yarn is too heavy for this trick, such that the resulting fabric would be too stiff, use a thinner yarn in matching color.

--TK