Published Jan 20, 2020
There are various processes for transferring images to clay, from photocopy transfers, silkscreening and stencils, to laser transfer decals and commercially made decals. There is also a process that's designed specifically for working with glaze. Pyrofoto is a product that works with the traditional photography concepts of exposing a surface to light through a negative, then developing, processing, and fixing the image.
Our own Jessica Knapp puts Pyrofoto to the test, and in today's post, she tells us all about the process and her results. Take it away, Jess! – Jennifer Poellot Harnetty, editor.
There are various processes for transferring images to clay, from photocopy transfers, silkscreening, and stencils to laser transfer decals and commercially made decals. There is also a process that’s designed specifically for working with glaze. Pyrofoto is a product—made by Rockland Colloid (www.rockaloid.com), the makers of Liquid Light photographic emulsion—for use on glaze-fired pieces. It works with traditional photography concepts of exposing a surface to light through a negative, then developing, processing, and fixing the image. However, unlike traditional photography processes, no expensive equipment, chemicals or darkroom are needed.
How It Works
Pyrofoto is a liquid sensitizer designed to be mixed with glaze and used on a piece that has already been glaze fired. The glaze/sensitizer mix is applied to an already glaze-fired surface, and exposed to direct sunlight, a work lamp, or a high-wattage (250-watt) halogen lamp through a high-contrast transparency image. (Note: Normal household incandescent bulbs will not work as they do not provide the right wavelength.) Where the Pyrofoto mixture is exposed to light (in areas not blocked by the ink on the transparency), it hardens like a resin and becomes fixed to the surface. The pot is then wiped or sponged with cool water to dissolve away unexposed areas, leaving only the glazed image behind. The piece can then be fired again to set the image permanently.
Creating an Image
First, choose your imagery and create a black-and-white transparency using an inkjet or laser printer or copier. High-contrast photographs, illustrations or your own drawings will work best with this process, so avoid images with lots of mid tones, or alter the image using photo editing software to increase the contrast.
Make sure your printer or photocopier is set to “best quality” before printing the transparency. If ordering the transparency at an office supply store, ask for a high quality print. This ensures that the black areas, which resist the light and therefore result in unexposed areas, are saturated and opaque. Remember that the black areas of your image don’t remain once the process is finished. Think of these areas as the negative space. If you want these areas of the image to remain, alter your photo to create an inverse image; make the white areas black, and black areas white.
To create a multiple-color image, you’ll need to do one of three things. Make a separate transparency for each color, just like color separations are needed for screen printing, work with a contrast between the base glaze and your Pyrofoto/glaze mixture, or selectively apply different Pyrofoto/glaze mixtures to the piece based on the colors in your image.
Mixing & Applying Glazes
Once you know the colors you wish to use, mix one part of the Pyrofoto sensitizer with one part of your liquid glaze by volume. If you use powdered glaze, reconstitute it to a thick consistency first (at least as thick as slip for slip trailing). Note: Wear gloves and a respirator while working with Pyrofoto.
Tip: For best results, use a thicker glaze with high colorant concentration. Watery glaze won’t coat well. If the color or pigment isn’t strong enough, the image will be faint.
Clean your already glaze-fired piece by scrubbing with powdered laundry detergent and rinse with hot water, then dry. Prepare test tiles as well to use as exposure test strips.
Apply a thin coat of sensitized glaze by brushing, then allow it to dry (figure 1). Next, apply one or more heavier coats. Dry thoroughly at room temperature. You can use a fan or a hair dryer on the cool setting, or let the pieces air dry over several hours. Note: It is much more challenging to apply Pyrofoto to three-dimensional forms. In addition to the recommended method, I also pre-heated some pieces to 200°F prior to applying the glaze to accelerate drying and avoid drips. Both methods worked, but the recommended method yielded a crisper image. Try both as your results may vary.
Exposing & Developing
Use your test strips to determine your exposure time. It will be between 5–15 minutes. My images required 15 minutes. If the unexposed areas don’t dissolve, the image is overexposed (shorten the exposure time). If all of the glaze washes off during processing, the image is underexposed (increase the exposure time).
Position the transparency onto your piece (figure 2). For flat tiles, the exposure time will be straightforward and based on your test strips. If you’re working on a curved surface, the time may be different if not all areas can be exposed at the same time. Set up multiple light sources, or add the image and expose it in sections.
After exposing the image, develop it by gently sponging or wiping with cool tap water (figure 3). Don’t use a lot of water as this will dissolve the image. I used a damp sponge. The unexposed areas, which look lighter or slightly greenish-yellow in color n comparison with the rest of the glaze, will gradually dissolve. It may take several minutes for the image to appear. Don’t brush or sponge aggressively as this may damage the image. For detailed areas, use a small, cut piece of sponge to remove the unexposed glaze. Note: The unexposed glaze should be collected in a bucket rather than allowed to go down the drain. Like other used glaze materials, it should be disposed of properly or fired in a waste bowl like other glaze scraps to render it inert.
When all of the unexposed areas are removed, blot and dry the image. If you want, you can apply a second color and repeat the process. When the glaze dries, fire the piece to the appropriate temperature.
The cup shown here has a shiny base and a shiny transparent Pyrofoto/glaze. It was fired to cone 4.
Pyrofoto can be purchased directly from the Rockland Colloid website, or by phone at 503-655-4152. Many of the company’s products are also sold through photo supply stores, such as B&H Photo.
**First published in 2011.