A couple of ideas on cord and goldwork edging of applique

General

From Grace Christie, Tapestry and Weaving :

The colour of this cord (used to edge an applique) is important, since its colour may increase the expanse of either the applied part or the ground.
Sometimes a double cord is put round, and in this case the inner one is attached to the embroidery before it is cut out of the frame, and the second attached afterwards. 
The inner one is often of a colour predominating in the embroidery, and the outer one of the colour of the ground. 
Gold cord is very usual; if a coloured silk one is used it must be a perfect match.
The ordinary twisted cord looks best attached invisibly; to do this, slightly untwist it whilst stitching, and insert the needle in the opening thus formed.
Some kinds of flat braids look well with the fixing stitches taken deliberately over them and forming part of the ornamentation.
Bunches of silk are sometimes couched round with a buttonhole or other stitch, but whatever the outline may consist of, it should be a firm bold line.

More on edging applique with “bunches of silk”

Couching is the name given to a method of embroidery in which one thread is attached to the material by another one.
Sometimes not only one thread but a number of threads are couched down together; or it may be cord, braid, or metal thread that is attached to the material in this way. Figure 88 shows some couching in progress.


Fig. 88.

The method probably arose through the difficulty experienced in passing either coarse or very delicate threads through a material.
Couching is constantly in use with gold thread embroidery, and it is further discussed in the chapter upon that subject, where also is described an entirely different method, which is to be recommended for couching other as well as for gold threads
Couching is useful in a variety of ways, e.g. for carrying out work in line or for outlining other embroidery, applied work for instance, which is frequently finished off by means of a couched thread; in the case of a difficult ground material, it is one of the most manageable methods of working.

A particular edging 

Source : http://chestofbooks.com/crafts/needlework/Embroidery-Craft-Of-The-Needle/Chapter-IV-Description-Of-Designs-Illustrated-Part-6.html

Plate No. 38.

Detail of cut linen, embroidered with coloured silks and silver-gilt and silver threads.
Italian, late sixteenth century 

Near the edge of the cut forms is a double silver-gilt thread; then follows an edging of green silk in button-hole stitch.
The stitch, while finishing the edge of the ornament, is carried over the silver-gilt threads, and secures them.
This metal thread is passed from one portion of the design to another, forming loops to assist in uniting the whole pattern.
The leaves and flowers are partially worked in coloured silks.

-- I don't like the 'looping' outside the appliqued pieces, but the green buttonhole with it's 'legs' extending over two couched silver cords sounds pretty