DEFINITION
A decal consists of powdered ground glass and metallic oxide pigments suspended in a temporary plastic film (vehicle) which is covered with a temporary plastic carrier (cover coat) and is printed on paper coated with either a water-soluble dextrin gum to enable its release during water slide transfer, or coated with wax or silicone to enable its release during heat release transfer. During the firing process the cover coat and vehicle burns away; the ground glass melts and encapsulates the oxide, fusing it to the substrate to which the decal was applied.
STORAGE
The ideal storage area has a controlled temperature of approximately 70°F and relative humidity of 50%. Air-conditioned storage is necessary in warm climates as heat softens the decal cover coat and causes decals to stick together. Decals should be stacked on edge to avoid this. Paper curl is normal if decals have been exposed to an adjustment in environmental humidity. Decals should not be folded or creased as this will fracture color films which will worsen during firing.
INITIAL TESTING
As many factors can affect firing results, initial testing is very important. Always test fire six pieces as an initial evaluation. To save good ware it is recommended that second quality pieces of ware be used in this initial test firing. If all results are positive from this initial firing, a second firing should be done with a dozen pieces of first quality ware. If any problems are encountered during test firings please make us aware with a telephone call, e-mail, or fax. Sending a piece of ware showing firing defects is essential to identifying the cause of the problem. The decal manufacturer is not responsible for lost ware, as proper test firing eliminates ware loss.
 TRANSFER
Cleanliness is extremely important during decal transfer. The ware to be decorated should be at room temperature or slightly warmer and free from any grease or dust particles. Pieces with complex curves tend to be easier to decorate with decal if the piece is heated to about 85°F-100°F before decal application. The decal will stretch more easily and wrinkles will be eliminated faster by applying the decal to a warmed surface. It is recommended to wash the ware prior to decal application since any contamination of the ware under the decal will lead to firing defects. The soak water for the decals should be 85°F. To maintain soak water at a constant temperature, a simple aquarium heater and thermometer can be a valuable investment. Distilled water should be used to keep it free of minerals or impurities found in many municipal water sources which may cause ghosting or hazing that outlines the fired decal. Soak decals a few at a time for 30-45 seconds or until the paper begins to uncurl, without allowing the decal to soak off the paper (decals can be removed from the soak water and stacked until they are transferred). The soak water should be changed frequently to reduce impurities and water soluble gum that builds up in the water. Always slide, do not "pick", the decal from the paper and apply face-up on the ware. Squeegee all excess moisture and air from under the decal by using a small rubber squeegee as a wiper blade. Finish by wiping the top of the decal with a damp lint-free cloth to remove any residual gum. When properly applied, a decal will not slide around on the ware. Check thoroughly for air or water bubbles to avoid blowouts during firing. Allow decorated pieces to dry overnight before firing to allow all moisture to evaporate as any moisture left behind will cause blowouts in the design during firing. Keeping the ware warm after transfer can be critical to smooth results as cold decal can stiffen, trapping air and moisture underneath.
FIRING
This final step is critical to successful decal decoration. A slow firing cycle is required for a kiln and longer preheat cycles for lehrs. A large amount of organic material is present in the decal vehicle and cover coat. These organic materials must be burned off at a slow rate before high temperature firing. Proper ventilation is critical during this stage of the firing cycle. The kiln door may be left open about one to three inches and any peepholes should also be opened during this stage to insure the organic materials are ventilated out and fresh oxygen circulates into the kiln. All organic material should be burned off between the kiln start-up and its reaching 800°F. At this point kiln doors and peepholes may be closed; however, minor openings in small tight kilns are a good idea for the duration of the fire.
The rate of heating during burn-off is critical to a high yield of good firings. 7.5-10°F per minute is considered safest, and this rate may compensate for minor defects in decal application. Much faster burn-off is possible if the decal is thin and the application is perfect. A pyrometer reading kiln controller is strongly recommended as heating rate, peak temperature, and heat soak times can be tightly controlled. Pyrometric cones placed in the center of the load, visible through a peep hole, are also a reproducible measure of heat work (heat x time) and may be used to check instrumentation of control firings.
The kiln door should remain closed until the load has cooled. Opening the kiln door too soon may cause the ware to crack due to rapid contraction and could present a danger to the kiln operator. All kilns should be ventilated to the outside by use of a hood.
RESULTS
A properly fired decal should have good color and gloss, and it should be free of imperfections. Some common firing defects and possible causes can be found in the Glossary of Common Decal Problems. Please be aware that decal construction must be very specific to work with the many various types of ceramic bodies and glazes as well as glassware. A decal designed for glass applications fuses at relatively low temperatures, and if placed on a hard glaze surface (such as a ceramic mug), it will not provide the detergent resistance that a properly fired decal constructed for ceramic applications will. Coefficient of expansion mismatch could also cause decal failure. It is important that the decorator provide us with the proper ware for fit and testing of each project submitted in order to insure a proper match between the decal and the ware.
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