Glass Transfer = Ceramic Decal

Printed transfers have been utilized for decades to make detailed images that are permanently applied to an almost limitless range of ceramic and glass products: drinking glasses, collector plates, bottles, jewelry, appliance components, sanitary ware, table settings, tile, cookware, pottery, and much more.

The terms "transfer" and "decal" are used interchangeably, representing the image that is printed separately and then removed from its backing paper to be applied to the final product. This unique manufacturing process uses special pigments called ceramic oxides that, when fired in a kiln, permanently bond with the substrate (base item).

Confused? Jump down to our glossary to clear up any new terminology!

It is important to note that ceramic decals are the name for printed transfers manufactured for a variety of substrates, including glass. They are called ceramic decals because of the pigments used, ceramic oxides. The major difference is that glass products must be fired at lower kiln temperatures and, therefore, decals for use on glass are built with specific pigments that will fuse properly in the lower temperature range. Any reputable manufacturer will tell you the ideal temperature at which their decals should be fired; custom manufacturers will work with you to make sure the range is appropriate to the product you are decorating.

Building a Transfer

Ceramic decals are created by screen printing onto a special paper. The paper is coated with either a water-soluble gum or a thin wax so the image can be separated from the paper after printing. The decal is held together and protected by a special top layer called the covercoat, which burns off during firing.

The pigments used in a transfer are selected specifically for the substrate to which it will be applied. Factors including the maximum firing temperature the item can bear and how it will be used by the consumer are especially important in creating a durable and saleable product. Glass generally fires several hundred degrees lower than similar ceramic items because the ceramic temperature is too hot for the glass - it would melt. Because the ceramic oxides require a certain temperature to properly bond to the substrate, a glass piece could not use a decal manufactured to fire at 1450°F.

The intended use of the product is important to both make sure the item will withstand regular wear, such as dish washing, plus ensure it meets all legal criteria. There are a number of federal and individual state regulations concerning lead (Pb) and other toxic heavy metals traditionally used in ceramic decorating. These metals are used to create bright and durable colors, although technology in heavy metal-free decorating has come a long way and is available from quality decal printers. More information about toxic heavy metal regulations can be found at http://www.unleadeddecal.com

Once the basic criteria are established, the pigments required to print the specific image are mixed and milled to create a smooth, consistent ink. The screen printing process uses one color at a time, layering them with a drying period in between each color. A decal can consist of only one to ten or more layers of color, precious metals, or conductive paste. After all layers of the design have been printed, the covercoat is applied with a final printing pass.

The expertise involved in ink formulation, printing detail, and final inspection make this manufacturing process as much of an art as it is a science. No two manufacturers (printers) operate with the exact same processes or quality standards.

Applications

Transfers offer several advantages over other methods of decorating glass. First and foremost, a transfer is printed on a flat sheet of paper instead of directly onto curved or irregular surfaces, resulting in superior accuracy and consistency from piece to piece. For similar reasons, decals are versatile in allowing detailed four-color process, tight registration, and various special effects like raised print or incorporating precious metals into a design. During decoration, significantly less set-up and clean-up time is needed for applying decals as opposed to a direct-screening process and decals are excellent for just-in-time production or interruptable processes.

While ceramic transfers offer many benefits, they cannot be the best decorating method for every project. The development work and fixed cost materials required for screen printing make small-quantity custom work less cost effective. Decals generally become economical with a minimum of one hundred printed sheets, which may equate to hundreds or even thousands of pieces depending on the size of the design.

Another consideration is the application process and time frame. The most common format of decals is for waterslide application, in which the base paper is coated with a gum that dissolves in water. After a brief soak, the decal is slid off the paper, directly onto the substrate (see photo below). A squeegee or lint-free cloth is used to make sure no excess water or air is trapped under the decal. It is recommended that waterslide decals be allowed to dry overnight before firing.

Another method, which is much faster because it is automated with a machine and requires no drying time, is heat release application. Decal paper for heat transfer comes in large rolls with a wax base that will melt and allow the transfer to adhere to its substrate. These are best suited to large industrial operations with consistently high volumes that can support the investment and space required for a heat transfer machine.

How to Purchase Transfers

Ceramic decals can be found most easily and in the greatest selection on the Internet. Some companies produce both a stock line of standard designs that can be bought in small quantities in addition to custom printing services where you provide the design and specifications. Some companies are focused on only stock or only custom manufacturing. A search for "ceramic decal manufacturer" should bring you a good listing of options.

Quality decal manufacturers will engineer the decal to work best with your specific substrate, firing environment, and other unique characteristics of your product. The bonding of a ceramic decal to its substrate is a chemical reaction that is most effective when all important variables have been taken into account.

Always be sure the firing range for the decals you purchase is within the temperature your ware, and your kiln, can handle. It's also important to remember that ceramic oxides can fire into different, generally brighter colors than you see on the pre-fired decal. If you have a fired sample of the decal or a quality image of how it will look once fired, base your purchase decision on the fired appearance rather than the covercoated, un-fired decal.

Custom Decal Manufacturing

In order to reproduce artwork or a specific type of image, a custom ceramic decal is necessary. You will need a high quality graphic (300 dpi/ppi at actual size) or at least an idea of the image you want and your budget for purchasing or licensing a copyright, or having it designed for you.

You may need to send a sample of the image (a lower-resolution web graphic or PDF, or a hard copy) prior to beginning custom work for a complete and accurate price quote. Depending on the design, there could be a number of printing screens required and/or special degrees of difficulty in reproducing the effects desired for your glass or ceramic piece. Ideally, you should also have a physical sample of the piece to be decorated; the manufacturer will use it for fitting purposes and may do a test-firing if you have a proof decal run. When you discuss your needs with the manufacturer, all of these details can be worked out prior to beginning the project.

The fixed costs of custom printing mean that the per-piece cost of a ceramic decal will decrease as your quantity gets higher. No matter how many decals you need, the printer will need to perform the same graphic manipulations, ink formulations, screen making, press set-up, and press clean-up. All these things must happen regardless of the quantity.

Glossary of Industry Terms

ceramic decal - a printed image used for permanent glass or ceramic decoration that is transferred from its base paper and applied and fired onto a substrate

ceramic oxide - an inorganic pigment that permanently bonds with ceramic and glass substrates when properly mixed in an ink formulation and fired in a kiln

ceramic transfer - another term for ceramic decal

covercoat - a layer of organic material that encapsulates the color and burns away during firing

firing - the process of heating a ceramic or glass item in a kiln at high temperatures. This melts the ceramic oxides in a decal and permanently bonds them to the substrate.

four-color process - printing system using four base colors (cyan, magenta, yellow, black) to produce a gamut of colors

gamut - a complete range of colors created by a set of like pigments

glass decal - another term for a ceramic decal specifically manufactured to fire onto a glass substrate

glass transfer - another term for a ceramic decal specifically manufactured to fire onto a glass substrate

heat release - decal application method requiring a heat application machine. Decals for heat release are printed on a wax-coated paper; the machine melts the wax and transfers the decal directly onto the substrate.

ink formulation - the mixture of pigments and a liquid base used to print a specific color

inorganic - a type of pigment, such as a ceramic oxide, that will melt and fuse to the substrate during firing

kiln - special oven used for firing glass and ceramics at high temperatures. Kilns are available in a range of sizes, loading formats, and firing capabilities.

palette - a range or group of colors with similar chemical composition

pigment - the base coloring substance, for decals a ceramic oxide, used to create the ink for printing a color

screen - a grid of fine wire stretched across a frame through which ink is pressed to reproduce an image

spot color - also referred to as "picked color," a specifically formulated ink printed alone or as a supplement to other layers. May be used to enhance four-color process.

substrate - the glass or ceramic base item to which a decal is applied and fused during the firing process

waterslide - decal application method in which the paper is soaked briefly in water, dissolving the gum coating and allowing the decal to be transferred by hand onto the substrate

About the Glass Transfer web site

Heinrich Ceramic Decal, Inc., a custom manufacturer of high quality transfers, created this site to serve as an informational resource on the use of ceramic decals in glass decorating. Heinrich has over 25 years of experience engineering custom decals for a wide range of product specifications. You can contact Heinrich by calling 1-508-797-4800, e-mailing info@heinrich-decal.com, or visiting their web site: http://www.heinrich-decal.com

© Copyright 2005 Heinrich Ceramic Decal, Inc. All Rights Reserved.