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Silk screen printing

Silk screen printing is one of the best options for hobbyists and potters to reproduce crisp and detailed decoration. But there are many details to know.

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Details

Historically, screen printing has been a popular technique to reproduce single or multi-color designs for ceramics and pottery (it has a long history in the tile industry, designs were screened directly onto flat tiles. In the process, a frame having a tightly stretched silk fabric holds an ink-blocking stencil. A rubber squeegee pushes the ink through the screen onto the surface below. When done well, good detail and crisp edges are possible. Potters use the process to create their own tissue transfers, these are normally done on leather-hard ware (but also doable on bone dry or bisque). Water slide decals can also be made effectively using silk screen printing. Although many books are available on the process, most people search videos instructional videos on Youtube. Supplies and equipment can be found on ebay.com or various online distributors. Of course, the inkjet printing process has replaced silk screening in many areas, that being said the latter still has some advantages.

The most important detail to consider is how to make the screens and prepare negatives. If you are serious and want to really invest in this technique a good start is to buy a 20x24 aluminum frames (like those used to print t-shirts) and clamp hinges to secure them to backboards. Prepare artwork to fill about 14x18in of that (most people will put many smaller designs inside this area and print them selectively onto transfer paper as needed). Take your artwork to a silkscreen printing company (there are countless t-shirt and uniform printing businesses everywhere) and have them expose and prepare the screen. These companies are busy, give them a few weeks to finish it and bring a few pieces of pottery as a gift, especially for the worker who actually made the screen (this will help grease the wheels the next time you come!). One caution is not to get too large a squeegee, most often you will be screening a subset of the designs on the frame onto a smaller piece of tissue.

For complete control of the process, equipment must be purchased. The main expense will be an exposure unit (a lightbox in which to harden the light-sensitive emulsion), this can cost $500-1000. A darkroom is needed, to prepare screens for exposing, and various chemicals and other supplies. Consider buying a multi-color press for maximum flexibility. These devices enable four screens (rotating about a center), each will accurately position over the artwork to print its color. Photorealistic results can be obtained using the standard CMYK color set. These units do take quite a bit of space. Used ones are often available on Ebay for surprisingly low prices (a few hundred dollars for example).

Of course, many potters and hobbyists use the simple DIY kits available online. Some of these even enable the exposure step using sunlight!

No matter which method, a negative must be made to light-expose the emulsion. Vector illustration software to produce a PDF file is the best option to produce crisp edges and high quality (e.g. Adobe Illustrator). To print negatives (using a laser or inkjet printer) buy clear acetate having an emulsion coating that holds the ink. These emulsion-coated acetates are not crystal clear, but the exposure unit has very bright light so they still work. Different types of these are available, watch a few videos and read about them to find the one best for your printer. Best quality is obtained using RIP software to control your printer directly to spray more ink to produce a blacker image. Certain brands of printers will work much better or will be better supported by the software.

It is common to use commercial underglazes for the ink, while most are intended for brushing some brands do have a consistency that is better for screen printing (e.g. ones the gel like Crysanthos, Speedball). Many people also make their own inks by mixing silk-screen mediums with a stain/melt mix.

The tile industry is a massive user of this process and has accumulated by far the most knowledge in the details of its use.

Many glaze defects are associated with the misuse of the silkscreening process.

Related Information

An underglaze tissue transfer with clear overglaze at cone 6

This was applied at leather hard stage on Plainsman M370, bisque fired on, dipped in clear G2926B glaze, then fired at cone 6. The transfer was purchasing online. Since the pigment contains cobalt it does feather somewhat at the edges, this would be less of an issue at low temperature.

Ceramic tissue transfers: Good goat, better pig

These are whiteware mugs (Plainsman M370) with tissue transfers and overglazed with G2934 matte (left) and G2926B glossy (right). The matte glaze is obviously not as transparent, but enough to transmit the underglaze color well (and soften the edges). The pig is a good demonstration of how crisp the edges of lines can be once you master the application of tissue transfer designs (they are very easy to smudge).

Silk screening using a professionally made screen

Silk screening is a popular decorating method. It is difficult to get a better quality screen than having an aluminum framed one made at a shop that specializes in this process (you can buy those hinges from a screen supplier). This screen is 16x20 inches and I have multiple designs on it (I made them in Adobe Illustrator). I am about to screen lettering and a logo onto a tile using an ink I made (because I have found drastically different melt behaviors in commercial underglazes). I find that simply mixing the ink with water to a very thick consistency works best (it is very easy to plug up the screen if you employ hardening mediums, they are difficult to wash out).

Why it is not a good idea to use straight stain

The logo on the left was rubber-stamped using and ink mix made of only glycerine and Mason 6666 black stain. The glaze is shedding off during firing. Multiple properties needed by a stamping ink are not present here. First, the stain dries as a powder, it has no hardening or bonding properties, glycerine is its only mechanism. Second, it is too concentrated, the black color is so powerful that it bleeds excessively into the overlying glaze. Third, it does not melt during firing so it does not bond with the body below. And, it either develops only a fragile interface with the glaze above, or sheds it off. The piece on the right mixes the stain 50:50 with a glossy transparent glaze (having 20% kaolin), it lays down better, accepts the overglaze layer better (because it has less glycerine), presents less problems in handling before glazing and it has no issues with the overglaze crawling off during firing. Black stains are potent, a 75:25 stain:glaze mix would work even better.

Underglazes melting very differently at cone 8

Commercial underglaze colors fired in a flow tester. Underglazes need to melt enough to bond with the underlying body, but not so much that edges of designs bleed excessively into the overlying glaze. A regular glaze would melt enough to run well down the runway on this tester, but an underglaze should not flow at all. The green one here is clearly not sufficiently developed, its base needs more frit. The black is much too melted, its base needs less frit. The pink and blue are also melting too much. Clearly, underglazes recipes need individual attention so they melt to the same degree.

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A professionally-made silk screen frame

Silk screen mediums

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