Lindisfarne Stones

I am going to embroider my carved stone dogs.  Not a separate embroidery using the same design, I mean the actual carving. I keep getting blank looks when I say this to people, but I think it could work!

It is possible to stitch stone - I have a very small piece by Clyde Olliver which has stitches worked through holes drilled in slate - but I don't want to do anything else that will affect my carving (if only because it would be too hard!).  This leaves embroidering around it in some way.

What I intend doing is effectively constructing a box around it, with the carving framed by the top.  Keeping on the Lindisfarne Gospels theme, I want to use a motif from there, though after all the zoomorphic designs, this time I want to use a regular key pattern.  These are used in the Gospels and in other items such as stone crosses of the same period, and so seem appropriate.

The key pattern I want to use is drawn on a diamond grid, and although I could draw up such a grid myself, I'm afraid I'm going to cheat slightly and draw it on squared paper.

I first drew a strip up the centre, as it seemed easier than trying to work out the edges first:

Then filled in the rest:

I still want the diamond-grid effect, so this is where the real cheating comes in: I scanned my hand-drawn grid, rotated the scanned image by 45 degrees, and squashed it slightly, so that it's wider than it is tall. This gives me the key pattern I was after:

I traced this onto strips, to form the design for the sides of the box:

To get the outline shape, I placed the stone piece under a sheet of perspex propped on books, and some tracing paper on top, and traced the outline:

I then traced the key pattern onto the same design:

Here's the completed design for the top:

I know what technique I'm going to use to stitch this - can you guess?