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.
13 hours ago