All Glossary

Ceramic Decals

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.

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Details

A method of printing designs (using ceramic inks) onto a transparent film, then transferring that to glazed ware (most commonly known as waterslide transfers). The film has a glue that holds it to a heavy opaque paper backing coated with a glossy release layer. On wetting (for the correct amount of time), the glue loosens and enables the transfer. As the decal dries on the ware the glue holds it in place. When fired, the very thin film backing material burns away leaving the ink to bond with the glaze surface. The film can accommodate quite a bit of irregularity in the contours of the surface.

Making these inks and silk screening the decals is typically beyond the ability of small manufacturers or potters. The inks are formulated to fuse as low as possible, which can be as low as cone 015 (the know-how to formulate compounds that melt that low is not common). Nowadays decals can be printed directly in an inkjet printer (fitted with ceramic ink cartridges), a laser printer (fitted with ceramic toner), or by silk screening (the latter transitioning to the former in recent years). These new technologies have many obvious advantages, and, some disadvantages. It goes without saying that complicated printer hardware, especially if it has been adapted to inks or toners made using abrasive ceramic powders, will have issues. The troublesome nature of running this equipment and the expensive supplies are the reasons why decals from online service providers are so expensive.

Where can you have decals printed? Etsy.com is likely the best place. A search phrase like "custom ceramic waterslide decals" should find them.

Some manufacturers of traditional ink formulations, mediums, silk screening, and ceramic waterslide decals have gone out of business in recent years and this has caused problems for companies who depend on them. Their formulations were lost in the process, notwithstanding that, the silkscreen decal process is still very useful. Are you an engineer who knows about these formulations? Would you be willing to share these with us so we can help others? Please contact us.

The inks and toner powders are specialized formulations of nano-powdered frit (bismuth-based) and stains, they form a glassy color at very low temperatures. However, since the designs are on the glaze surface, they must endure the full forces of wear and tear to which the piece is exposed. Since these inks do not contain the stable silicates that a glaze does (because they need to melt so low), they are more subject to abrasion and degradation. Decal firings only go to around 1600F (each decal manufacturer will have specific instructions). The underlying glaze usually does not melt enough to bleed their edges. This stable surface enables great precision of design, full-color photos can thus be produced. That being said, the colors are not as accurate as regular print, only a subset of the CMYK color set can be printed (and even a smaller subset of the RGB colorset used on video monitors).

Firing decals on large pieces can put you on a collision course with ware cracking - resulting from stresses in passing up or down too fast through quartz or cristobalite inversions. It is a necessity to have a programable kiln controller to slow down through these periods.

There is a serious issue to think about if you are planning to introduce decals into your production, decal-printing websites seldom even mention this. Many glazes are reactive fluid melters (high boron, zinc, lithium) and begin to soften at decal temperatures. These will often form pits, pinholes or even blisters during the firing-on of the decal, ruining the piece. The higher you fire the ware originally and the later the glaze melts, the less likely this problem will be. Even if it does not melt, the glaze may have a visual character (color or surface texture) that is a product of crystallization during cooling, these crystals could easily be affected during a decal firing. Thus, low-fire glazes will, of course, be most susceptible to this. Mid-temperature glazes having the lowest possible B₂O₃ content, yet still melting enough, will be more likely to work. Cone 10 ware will be even better/ fast fire glazes melt late and will thus work the best.

Related Information

Gold decal on a gunmetal matte black glaze

This is a cone 6 porcelain mug with G2934 matte glaze (with 6% black stain added). We get this satin matte effect in our test kilns using the PLC6DS schedule. Larger kilns cool slower so this glaze turns out too matte in them, we deal with that by increasing the percentage of glossy base (this is a 15:85 blend of G2926B glossy and G2934 matte). The gold decal is from Sanbao Studio. On the left, it has just been applied, other than the glossy finish revealing its location, no gold design is visible. But, after the decal firing, using the MDDCL schedule, we get the result on the right.

The G2934 base matte recipe is good for decals because it has a very low B₂O₃ content (unlike high boron glazes that can begin to melt very early, even in a decal firing, and alter their degree of matteness or even produce tiny pinholes or blisters). G2934 can tolerate some high-boron G2926B glossy, enough to de-matte it, and still work well with decals.

Decal on a raw body surface

Fired in a standard decal firing. The glaze on the tile has helped fuse it to a glossy surface. Has worked well except for adhesion problems during application (because the porous body adsorbed all the water immediately). If the tile had been soaked previously it would have been better.

What is that glossy square around the decal?

An example of a digital decal that has been fired at 1500F onto a matte cone 6 glaze. Notice the glossy, square around the graphic. This is where the decal paper was cut prior to transfer. This glossy layer appears by design, the decal paper has a thin layer of glaze and your inkjet design is printed, reverse reading, onto that. After transfer and firing that glaze thus insulates the color from coming into contact with anything that might leach it. It is thus wise to trim carefully around designs such that the glossy pattern does not detract from the appearance (as it does here). You can get decals without the glaze covering, but may not melt enough to be durable on the glaze surface.

Why did this piece come out of a decal firing crazed?

This Cone 10 matte mug has been refired to attach decals. The fired matrix of the body is now brittle and dense and contains millions of quartz grains of many sizes. During the refire up through quartz and cristobalite inversions each of them experiences sudden volume increases. This does not happen in the glaze because its quartz particles were dissolved in the melt and converted to silicates during the previous glaze firing. The suddenness of the expansion depends on the rate of temperature increase and its extent depends on the size of the quartz particles. The body's passage through these two zones stretched the glaze and cracked it. Had the glaze fit been better (under some compression) it would likely have been able to survive.

Why has this platter has cracked in half during a decal firing?

Your ware is fairly thick. It was already vitrified in a previous firing. It now must climb and fall through quartz and cristobalite inversions during a decal firing. The firing schedule provided by the decal supplier ramps up very quickly. The result? A cracked piece.

Can a decal firing melt a glaze? Yes!

Typical zero-boron high-temperature glazes will not soften in a 1500F decal firing. But low-temperature glazes will (especially those high in boron). Even middle-temperature ones, especially those having significant B₂O₃, can soften. G3806C (right), for example, is reactive and fluid, it certainly will. Even G2926B, which has high Al₂O₃ and SiO₂, has tiny pits (because of the amount of B₂O₃ in contains). In serious cases, they can bubble like the mug on the right. What happened to this one? Steam. It was in use and had been absorbing water in the months since it was first glaze-fired at cone 03. The one on the left was not used, but it did have some time to absorb water from the air, it is showing tiny pits in the surface. Even if moisture is not present, on refire low fire bodies continue to generate gases of decomposition that affect glazes. Each decal manufacturer has a recommended firing temperature, that is for their decals, not your glaze.

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