The bones in the corset need to be housed in something, so, bone casing. If you haven't purchased pre-made bone casings you can make your own. I construct casing based on the construction of the post Edwardian corset use to make the pattern for the Foundations Revealed article. Here is a detail of the corset backlit so you can see how the casing was built.
It is just a strip of fabric with the edges folded under. I make casings using bias strips of coutil because I've found the bias makes the casings lie smoother against the curves of the body, but you can cut them on the grain too. Either way will work. If you will be making casings you'll need coutil, a ruler, a pencil, scissors, and an iron. Start by drawing a line 45 degrees to the grain of the fabric.
If you don't have a triangle you can measure from a corner along the selvedge, mark the same distance on the cross grain, then connect the points. Cut strips of fabric 1 7/8 inch wide. The casing needs to run the length of the corset so make sure the strips are long enough. If you have a 25mm bias tape folder you can pull the fabric through.
If not just fold the edges so they barely meet in the middle and press.
That's it! If you need bias trim to finish the top and bottom edges you'll make it the exact same way. Tomorrow we'll stitch the casings to the corset and Friday we'll attach the back facing.