I've looked up fray check, and I'm uneasy about using it as apparently it's acidic and can damage fabric. I think the embroidery is enough to keep the fraying from getting worse at this stage, it was more that it looked messy and wouldn't hold up to washing.
Oh, that method! I use that every time I make binding! Thank you for explaining, it made perfect sense.
The ribbon has arrived and looks very nice. It's a great colour match, it will blend in a lot better than I thought. Folding it over is going to be awkward for any seam which meets the edge of the block at anything other than a right angle, but I'll just have to fold it and roll it and fiddle and pin it into submission.
Does anyone have thoughts on what stitch will look best to hold it down? Hand embroidery stitches, remember. I can't use a machine and anyway, whatever I do for this will only go into the batting but not end up showing in the back. Blanket stitch again? Going straight up and down so that the stitching ends up being a row of little diagonal lines? Cross stitch? Should I cover a lot of the ribbon with stitching or leave most of it visible, and should I pick a matching thread or use a selection of the #8 perle threads from the quilting to provide some contrast? My current instinct is telling me to keep it unobtrusive, the heart is already enough to grab the attention with that block.