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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

Silk screening using a professionally-made screen

Silk screening is a popular decorating method. There is no better way to get a quality screen than having an aluminum-framed one made at a shop that specializes in this process (e.g. t-shirt printers). You can buy those hinges from a supplier online. This screen is 16x20 inches and I have multiple designs on it - I made them in Adobe Illustrator, which enables a vector graphic original that gives superior quality. I am about to screen lettering and a logo onto a tile. Although companies like Speedball, Amaco and Mayco make inks for this purpose, I am using an ink I made by mixing a black stain into a ceramic medium and adding enough water to achieve a viscous gel.

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 and is made using the silky screening process. Since the pigment contains cobalt it does feather somewhat at the edges, this would be less of an issue at low temperature.

Here is motivation to make your own underglazes!

Commercial hobby underglazes are high in stain and very expensive. But does expensive mean suitable? To help answer we have over-fired these commercial products in a melt fluidity tester (to cone 8). They are recommended for use from cone 06-6 (some can go higher e.g. the green). Underglazes need to melt enough to bond with the underlying body, but not so much that opacity is lost (any melting loses opacity). Excessive melt can also cause design edges to bleed. To work well at greater thicknesses, underglazes need to have a firing shrinkage similar to the body (an ill-fitted underglaze and body forced into marriage are eventually going to divorce, in the form of flaking or cracking at their interface). Thus, while a regular glaze would melt enough to go well down the runway on this tester, an underglaze should not flow at all. At this temperature, none of these have achieved the right degree of maturity (the green is too refractory, the others over-melt to varying degrees). The only one that has a chance of suitability at cone 6, two cones lower than this, is the blue. Clearly, the base recipe and stain percentage in each underglaze recipe color needs attention, if that can be achieved all of these would mature to the same degree.

When a DIY black underglaze makes sense

Black brushwork needs to go on thick enough in one brushstroke. Commercial products we have don't do that - thus my motivation to work on this. Another issue is that they try to cover too wide a firing range (thus they melt too much at the high end and not enough at the low end). I am experimenting on cone 6 Polar Ice porcelain jiggered bowls using G2926B dipping glaze. The base underglaze recipe here is a 90:10 MNP:nepheline syenite mix (you could use your own porcelain instead of MNP and feldspar instead of nepheline). To that, I add 15% black stain, 1.5% CMC gum and 5% bentonite. With the CMC gum and bentonite, and blender mixing, a brushable consistency that stays put can be achieved at a fairly low water content compared to commercial products (enabling it to go on thicker in a single brush stroke). Assuming application at leather hard state, the drying and firing shrinkage can be matched to the body by varying the plasticity of the porcelain used (e.g. the percentage of bentonite it contains). And the percentage of stain can be tuned for enough color but no bleeding, bubble clouding or crystallization. And we can adjust the degree of maturity by varying the proportions of MNP and Nepheline (commercial underglazes often melt too much by cone 6 and fade and diffuse as a result), this one stays opaque black.

Underglazes suitable for making silk screen transfers are another special case. The ideal one needs to cover well like this one. But it also needs to gel and harden enough to hang onto the paper but not so hard that it does not separate and transfer to the ware. Commercial products for brushing are unlikely to be optimal so it makes sense to mix your own and experiment with different amounts of gum.

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Silk screen mediums

A professionally-made silk screen frame

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