Ahh, Pinterest! What did we do before you? I found this technique there. It was really intended for screen printing t-shirts, but it seems to me it would work well for slip transfer also, especially because the resulting screen is fabric, which you could wrap around a three-dimensional form.
I used an old sheer curtain, which had already suffered from too much cat attention, stretched over a small embroidery hoop. The hoops are like a dollar and a half at AC Moore. While you are there, pick up some Mod Podge and a foam brush; then go next door to Staples and grab some shipping labels. I got 5163s, a little bit bigger than business cards, but they make larger ones, up to full sheets, if you have a bigger image in mind.
Draw, the cut your shape out of a shipping label. Peel off the back, and stick the shape to the sheer fabric, on the "up" side of the hoop. Press the edges down carefully; if they aren't thoroughly stuck down, your shape will have an irregular edge.
With a foam brush, paint the Mod Podge onto the screen, brushing outwards from the sticky label. I applied it pretty thickly. Note: Do not apply the Mod Podge all the way out to the frame, or onto the frame itself. Turns out Mod Podge is sorta just Elmer's Glue in a snazzier jar! It will stick the screen to the frame pretty securely. Yeah, now ask me how I know that...
While the Mod Podge is still wet, peel off the sticker. I
found a needle tool helpful here. It will take a long while for the
screen to dry; at least overnight. Store it horizontally! Bad things
Once it's dry, remove it from the frame and cut it to a convenient size.
Use it by pressing the fabric to the clay surface. Press firmly to stick it to the damp surface. (Here I used a different stencil I had made earlier, as the first one was not quite ready yet. ) A pony roller helped to make sure it was well stuck.
With a brush, press your colored slip (or maybe glaze? Haven't tried that.
Somebody try it and get back to me) through the screen to make your
The result is a sharper image than one would get with a cut sponge, but softer than a decal. It worked on vertical surfaces also.
A note: Mod Podge is not waterproof, though it is water resistant. Rinse your screen carefully between uses, and immediately when you are done with it, so you don't have to scrub.
2 hours ago