So, making the things. For opaques, it's pretty easy: I fire a layer of counter-enamel on the back of the copper tile, pickle it to get rid of the oxides the firing made on the front, then sift the enamel color onto the front and fire it again. Done.
But the others? Not so easy! Since you can see through them, what's under them is pretty important- sometimes vital, since some metals actually change the colors of the enamels. And it would be very sad if the pretty deep pink rose one had planned ended up being an ugly mustard color!
So: sample (or test) tiles. Mine test a color over 5 things: bare copper; copper covered with flux (clear, uncolored enamel in enameling); white enamel; fine silver; and fine gold. For some colors a test over fluxed silver would be nice- but I can usually make an decent guess without that, and it'd add a lot to the complication of making the things!
So here's what I do: First, the counter-enamel, sifted and fired. (This is necessary so the stresses on the front and the back of the metal are balanced.) Then, I sift flux over a bit more than half of the tile, and opaque white over an additional quarter of it, then fire. Now, sifting dry enamel in 2 colors without messing it up isn't altogether easy, especially on a small tile (mine are about an inch square), but that's not the fun part. No, the fun part is the next step: applying the silver and gold. Actually, the silver's not bad. I have some very thin foil I use, and I can cut it with a rotary cutter (like quilters use) into 0.25 in (6mm) squares, and these squares are not particularly fragile. The gold's the fun part. I'm using gold leaf, which is, literally, so thin you can see through it and which cannot be touched with pretty much anything because it'll stick... unless you want it to, of course. So I wet down the tile (this is on the flux) and make my brush semi-soggy, and approach the foil. If I'm lucky, the brush grabs a corner, and the foil sticks to it, and a reasonable-sized piece tears off and I can then float it on the tile. But luck isn't guaranteed. I swear, once I use up this leaf, I'm replacing it with gold foil- yeah, it's about ten times as expensive, but I think it'd be worth it! Anyway, then I let the glue dry, and fire again, which makes the foil and leaf stick.
And only then can I clean off the bare copper, sift my color over the whole mess, refire- and then organize it into my book, so when I'm designing a piece I can look through it and have a pretty good idea what will happen if I use any individual color.
Today I got quite a few sample tiles all the way through firing on the metals. So tomorrow I can clean off the copper, and then actually test some colors! That's the fun part, despite the organizing it requires.
With the tiles I've done, I should be able to test all the colors I've acquired recently(ish) from Japan and Schauer. And maybe a few of the other ones I have waiting...