Working with Heavy Metal Free Glass Decals
An overview of color palette options in glass decorating and the
challenges presented by regulations limiting heavy metal content.
by Michael J. McCall
April 19, 2005
Decorating glass with heavy metal free inks is more necessity than choice with today’s state and federal regulations. Below I describe the various inks available to decorate glass. Each range of color has its merits and drawbacks. Understanding the uses and limitations of each color palette is important, as the glass decorating industry is quickly moving away from the use of heavy metals.
There are three primary color palettes used for printing decals that are to be fired for the permanent decoration of glass. Soft colors, which are fired in the 968°F - 1076°F (520°C - 580°C) temperature range, are used on items such as leaded crystal and stemware. These soft colors have an excellent range of hues, gloss easily, and are resistant to pin-holing as these heavily leaded pigments flow well during firing. Soft colors offer almost no dishwasher detergent resistance. Cadmium is also present in many of the colors in this range.
Acid resistant colors have proven popular for their ability to survive the effects of dishwater detergent. This palette is often used with tumblers and shot glasses. The acid resistant colors are fired in the 1150°F - 1200°F (621°C - 649°C) temperature range. They contain lead and cadmium that make excellent reds, yellows and oranges. This palette has no pinks or purples available. The high temperatures required by these colors limits their use to glassware sturdy enough to withstand the hot firing cycle.
Heavy metal free colors have good cyan, magenta, yellow and black, which makes them suited for four color process print. Some lead-free colors may contain cadmium to make strong reds, yellows and greens, which are otherwise lacking. To get this palette to properly gloss, the firing temperature must be in the 1150°F - 1200°F (621°C - 649°C) temperature range.
Working with heavy metal free glass colors poses some challenges for the decorator. Not only does this range of color need high temperatures, it also requires a much gentler firing cycle that provides a slow ramp in the earlier stages of firing to allow the organics to burn off slowly. An aggressive temperature ramp results in disruptions in the ink film as the organic covercoat and medium burn away. As the colors mature later in the cycle, they do not flow well to smooth out any disruptions. It is highly likely that firing cycles used for leaded decal will need to be adjusted to successfully fire unleaded decal. Lead-free decals have virtually no dishwasher detergent resistance.
It is often necessary to print a layer of white under heavy metal free colors to improve their brightness and opacity. In addition to exhibiting poor opacity, the colors need to be printed as thin as possible to avoid problems with the difference of the coefficient of expansion between the glassware and the ink. Printing too heavy a layer will result in the color coming off the glass, as the color and glass expand and contract at different rates.
Understanding the color and firing limitations and working closely with the decal printer and decorator can produce attractive products decorated with heavy metal free materials. As evidenced with ceramic tableware, the process of moving away from heavy metals takes time and patience to be accomplished.
Michael J. McCall is the president of Heinrich Ceramic Decal, Inc. (heinrich-decal.com), a ceramic decal printing company that has been servicing the glass and ceramic industries since 1980. He can be reached at 508-797-4800 x256 or by e-mail
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