|Monthly Tech-Tip |
Silk screen printing is one of the best options for hobbyists and potters to reproduce crisp and detailed decoration for their ware. But there are many details to know.
Screen printing is a popular technique used to reproduce single or multi-color designs for ceramics and pottery. It has long been used in the sign painting and garment industries. In the process, a frame having a tightly stretched silk fabric holds an inking blocking stencil and a squeegee is used to push the ink through the screen onto the surface below. Great detail and crisp edges are possible using this technique. It was popular for many years among slip casters but more recently potters have adopted it also. Many art schools also teach it. Of course, it is possible to screen directly on to tiles and flat surfaces. However be aware that this is only practical if they are truly flat (like a commercial dust-pressed bisque tile). On irregular surfaces you must print reverse-reading onto a transfer (e.g. tissue paper) or right-reading onto decal paper and then transfer that to the ware. Tissue paper transfers can be done on leather hard, dry or bisque ware; decals are transferred after glaze firing and then burned on in another firing. Although many books are available on the process, more and more people search videos on youtube to learn it. Supplies and equipment can be found on ebay.com or various online distributors specializing in the process.
The most important detail to consider is how you will make your screens and prepare your negatives. To start it is best to buy a 20x24in alumina framed screen and a couple of clamp-hinges to secure it to a backboard. Then prepare your 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 silk screen printing company in your city (there are countless t-shirt and uniform printing businesses everywhere) and have them expose and prepare your screen for you (they may very well charge you as little as $20 to do this). These companies have busy times during the year, depending on when you will need to be patient, give them a few weeks to finish it and bring them 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!). Then get a squeegee (the right size to print the individual designs on the screen, not a huge one) and you are ready to go.
If you wish to have complete control of the process you will need to buy equipment. The main expense will be an exposure unit (a light box in which you expose the light sensitive emulsion under the negative you have made), it can cost $500-1000. You will also need a darkroom in which to prepare screens for exposing and various chemicals and other supplies. If you wish to print multi-color consider buying a multi-color press. These devices enable you to have four screens (rotating about a center), for example, and accurately position each over the artwork to print its color. Photo realistic results can be obtained using the standard CMYK color set. These units do take quite a bit of space, but used ones are often available on ebay.com for surprisingly low prices (a few hundred dollars for example).
No matter which way to choose, you will still need to make the negative used to burn the screen. Vector illustration software to produce a PDF file is the best option to produce crisp edges and high quality (e.g. Adobe Illustrator or iDraw on the iPad/Mac). But if you must you can draw by hand, scan and use a bit image editor (like Photoshop). If you want to print your own negatives (using a laser or inkjet printer) you will need to buy clear acetate having an emulsion coating which 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 or type of printer. If you print yourself there the blacks will almost certainly not be black and opaque enough. Many people deal with this by simply printing twice (especially on laser printers). But a better option is to buy RIP software to control your printer directly to spray more ink and produce a blacker image. If you want to do this beware that certain brands of printer will work much better or will be better supported by the software.
It is common to use commercial underglazes for the ink, most are of course intended for painting on but some brands do have a consistency that is acceptable for screen printing. However, since ink consistency is so important for the best results, many people make their own by mixing silk-screen mediums with a stain/melt mix (if you make your own ink please check the "Ceramic Ink" link below for more information).
There is no substitute for watching and listening to someone experienced in the process explain how they do it. If you can learn little details of the process that relate specifically to ceramics (that are not covered in books and videos) you will save yourself a lot of time and expense. Then you make make the process your own and improvise from there.
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 misuse of the silk screening process. If you are planning on using this method for printing ceramic decals in production, beware that you are adding an extra layer of complexity, with that comes a whole new set of production demands (and potential problems).
Blend the two types, permanent and washable, with a powdered colorant, in the proportions appropriate to get as much hardness as possible but not so much that it is difficult to clean up the screen. The powder should be a ceramic stain mix with a melter medium (a glaze or frit).
It is aluminum and was made in a t-shirt printing shop from a negative created in Adobe Illustrator.
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).
Commercial underglaze colors fired at cone 8 in a flow tester (this is another good example of how valuable flow testers are). 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 flow much less. The green one here is clearly not sufficiently developed. The black is too melted (and contains volatiles that are gasing). The pink is much further along than the blue. And cone 5, these samples all melt significantly less. Clearly, underglazes need to be targeted to melt at specific temperatures and each color needs specific formulation attention. Silk screening and inkjet printing are increasingly popular and these processes need ink that will fuse to the surface of the body.
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.
You can make your own ink (or buy it) and apply it to ware using various methods (e.g. rubber stamping, silk screen, inkjet decals).
Ink Jet Printing
Ink jet printed decoration is now pervasive in all parts of the ceramic industry. And in hobby also.
This process of printing a design (using ceramic inks) onto film-coated paper to create a waterslide transfer. On wetting, the film decal can slide off the backing on to the glazed ware.
Screen printing on Wikipedia