Here are the enamel pieces, unframed and mounted on their cardboard backing:
Using a really small angled brush with firm bristles, I carefully painted around the enamel with some leftover paint (the same blackish greyish mystery mis-tint I used for the railing, the custom frame for the black white painting, the dipped stool and about a million other DIY projects. I love this magic colour). Here's what they looked like when I was done painting the cardboard mount:
I let the paint dry a few days to fully cure, then I popped the enamel landscapes into four Ikea frames. I love, love, love the result. The little strip of almost-black makes each piece POP and keeps them from getting lost against the white frames, mat, and walls. I opted to hang them in a vertical row between the curtains. That space always needed something.
Even from a distance, these little gems still pack some punch and I like how they connect the cooler and warmer colours in both the living and dining room. Plus, the black makes sense with the black accents splashed around both space, including the frame of the new dining room painting and the curtain rods. I'll definitely consider just painting a backdrop (even if I have to mount it on some cardboard myself) the next time I have some art that needs a custom mat.