We all remember those decals that come with model airplane kits we built when we were kids. I’m talking about the ones that you soak in water until they float off the backing paper, then you slide them into place on the model airplane and let it dry. It is possible to make those yourself.
On my page (TODO: Not yet written) on PCB fabrication, I described my limited success with the toner-transfer PCB products. But I have found the water-based products quite useful for making decals. You need the toner-transfer paper that works with water. Pulsar’s Toner Transfer System or Tekniks’ Press-N-Peel Wet. The Press-N-Peel Blue kind won’t work.
The water-based toner-transfer paper is coated with a thin layer of some water-soluble stuff. You print your decal imagery directly onto the coated side of the paper, just like you would if you were going to make a PCB with it. If you were to just soak it in water now, then when the soluble layer dissolved, all your imagery would break up and float away in the water in a million pieces. We need to hold it all together while moving it into the place on the surface.
To solve that, I use a few lights coats of a spray lacquer. Multiple light coats, with time to dry between coats, will prevent drips and runs. After the lacquer has dried, you can drop the decal into the water. When the soluble coating is dissolved, the lacquer will float off, and take the toner imagery with it, all in one piece. It’s very fragile, so the best way to apply it is to put the piece to be decorated into the water too, and float the decal over to it in the water. If you need to lift the decal out of the water, you probably want extra coats of lacquer to make it stronger.
With typical laser printers, this technique only lets you get black lettering on a clear background. Using the metallic special effect foils such as GBC Foil (I found it at Staples Business Depot), you can get other colours. Only metallic colours, unfortunately, but maybe other colours will come on the market.