Plate application
Plate is a thin, flat metal that can have a smooth or textured surface. It can be used flat or over padding (hard or soft string), and may be stitched so that it is folded back on itself. Either no gaps can be left; gaps left unfilled; or gaps left and filled with decorative stitches, beads, or chips of metal.
Plate was evidently in use in the 17th century as it features on the reverse of a pocket book from that date, currently held by the Victoria and Albert Museum, London.
Method
Make a loose stitch on the fabric, positioned where you wish to attach the end of the plate.
Creating a hook at one end of the plate using a pair of tweezers and hook the end of the metal through the loop.
Pull the thread tight so that the plate lies securely against the fabric.
Place a second holding stitch over the plate, abutting the other side of the padding.
Pull the thread firmly to form a tight stitch.
Fold the metal back across the padding at a slight angle, ensuring it covers more of the padding while at the same time overlapping the previously placed plate. Secure it with a holding stitch worked close to the padding, as in step 4.
Continue working back and forth across the padding.

Common uses
Embroidery Techniques
Related Stitches
Identifying Plate application
Attaching plate over soft string can be identified by the flatness of the metal being used (as opposed to purl which is a rounded metal thread with a hollow core) and by the raised effect that is created by the soft string padding.
References
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Helen McCook, RSN Essential Stitch Guides: Goldwork (2012)
Examples of Plate application

Triptych 2, RSN Collection No. 587
