First of all, let me just say that this is my first attempt at making a silk screen and I have little experience transferring underglaze images onto clay pieces, so bear with me, please.
Making the Screen
I am working primarily from the book Image Transfer on Clay by Paul Andrew Wandless, though I have seen a couple of demos of the technique. There are also many good Youtube videos about making the screens. You will need a pre-stretched silk screen, or you can make your own, plus some Diazo Screen Printing Emulsion (I used the Speedball brand). Working in a darkened, but not totally dark, room you will mix up your emulsion and then apply a thin layer of the emulsion on the screen using a squeegee for screen printing. Be sure to follow the directions for mixing the emulsion. I used a little too much water for mine so it went on a bit unevenly, but it seems to work OK. Now you will want to store your screen in a light proof area (I used a cardboard box in a low light room) for 24 hours or so. You can also get pre-emulsified screens from Ezscreenprint.com.
Once the photo emulsion on your screen has dried, you can burn your image. I decided to start with a simple image that I had downloaded from the internet. After laying out my image in various sizes in a word processing program, I printed the image on a sheet of transparency film that I purchased from my local office supply place. Be sure to get film that is appropriate for you type of printer and make sure you are getting a nice, clean print. If there are printer lines on your image, there will be printer lines on your screen. You will now lay your transparency film down on your treated screen and secure it with a piece of glass to hold it flat. I used my photo lights aimed directly at the screen for fifteen minutes to expose the screen, but you could try other light sources including the sun. Your exposure times may vary, though, so you will need to experiment a bit.
Once the screen has been exposed, wash the screen under a stream of warm running water. May need to use a soft toothbrush to push some of the emulsion out of the unexposed areas to get them fully clean. Now leave your screen out for a day or so to allow the emulsion to fully cure before using.
Using the Screen
I have only tried using my screen with underglazes but would eventually like to use it to make some color decals that I can put on over glazes.
I choose to print my images onto sheets of paper and then transfer the images onto my pots, but some people will screen print directly onto clay. For making the paper transfers, place the screen on top of a sheet of paper and then use a squeegee to lay a thin film of underglaze onto the paper. You can then let these sheets dry and use them as needed.
To apply the image onto a leather-hard pot, use a damp sponge to wet the area you wish to apply the image onto. Now cut out the image and paper that you wish to use. Using your damp sponge, start at the center of the image and gently press down on the paper, underglaze side towards the pot, and gently work your way outwards, trying not to crease the paper and applying just enough water to be able to see the image through the paper. Now use a red rib (the really soft ones) to gently smooth out the paper and secure the image to the pot. I like to let the paper and image sit for a minute or two and then I carefully peel the paper off the pot. I don't worry too much about any bits of paper that stick to the pot since they will burn off in the kiln .
I'm sorry I don't have many images for you guys, but Wandless has step by step directions in his book so check it out.
And thanks for checking out my blog. Let me know if you have any questions about what you see here and I will try and answer them ;)