I like to make durable surfaces using resin and small pieces of salvaged metal. I learned about MirrorCoat(tm) from Darin Montgomery, furniture designer-builder and owner of Urbancase. Nick Gucker at System Three Resins was very helpful, by phone and email, when I had technical questions about its use.
I start with an image on paper, often a detail from my collection of vintage travel postcards, which I glue to the clean and sanded metal. I may drill holes in the upper corners of the metal at this point, if it's to be a hanging piece. I use discarded cookie sheets to place my metal pieces on. These are handy for several reasons: the lip on the sheet prevents over poured MirrorCoat from oozing everywhere, and when they're done curing, a quick twist of the tray releases them.
I wear thick rubber gloves (latex ones can stick and pieces may remain on the working surface) and tie my hair back. I mix MirrorCoat according to the instructions and pour it over my metal pieces.
Unless I have a fairly dust-free workspace, I find a cardboard box large enough to fit over the tray, which allows good airflow while keeping debris off the resin. After they've cured thoroughly, I pry the metal pieces off the tray, use a rasp to get the big over pour chunks off, and sand the surfaces, being careful not to over-sand the sides (this can create thin spots that could let moisture in, undesirable if I'm planning to use them outdoors. Also, if the MirrorCoat does not entirely encase the metal piece, it may not be suitable for wet environments, as the metal will begin to rust, and the resin will begin to resist, rather than seal, the metal.) I sometimes pour a second coat of resin at this point, allow it to cure, then re-sand. I like to apply a UV-resistant spray as a last step. MirrorCoat creates a translucent finish that adds depth and glint to the image beneath.