Decals offer an opportunity to add decoration to ceramic and glass ware without the time and skill required for hand painting. When properly applied and fired, decals can add colour, texture, design and personalization to a piece.

To achieve professional results with decals, it's important to understand how to select, apply and fire the decals.

• type of decals
• different decals are made for glass and ceramics
• ceramic decals often fire hotter than those for glass
• application
• decals must have good contact with the surface of the ware
• all wrinkles and bubbles need to be smoothed away
• avoid tearing the decal
• firing
• decals are generally low firing - cone 022 to 016
• check the package for the proper firing range
• venting
• decals contain lots of organics which need to be burned off
• often smelly fumes result during decal firings

A decal isn't fired that much differently than any other piece of ware, although there are some special considerations.

1. Venting is very important to good results with decals - especially to get true colours.

Problems related to venting include:

• poor colour development
• a cloudy or hazy appearance
2. Proper heatwork is also an important factor. Decals that are under or overfired may exibit the following:
• faded colours (overfired)
• colour shift (underfired)
• decals rub off (underfired)
• dull appearing metallics (underfired)

Because the colours on decals can so easily be affected by the amount of heatwork they receive, we recommend test firings to determine the best firing range.

Use a series of witness cones to fire samples of the decals on tiles or blanks. Make several firings and then select the fired appearance which looks the best.

Colour Development

Cloudy looking decals or decals where the colour is not bright need to be burned out and carbon monoxide fumes have to be removed from the kiln.

Manual venting by propping the lid and removal of peephole plugs will improve the firing, but may not help bring enough air to the bottom of the kiln or to distribute it evenly throughout the load.

A downdraft vent system will ensure sufficient air is brought into the kiln and circulated throughout.

Measuring Heatwork

Heatwork is another critical factor in the colour development of decals.

Fading, Shifting and dullness are signs of too much or tool little heatwork. This is also true when decals rub off after firing. (White or blank spots or burned off areas are generally related to application, not firing.)

Use witness cones to measure heatwork and to check the heat distribution in the kiln. Firing to a temperature or firing to a Kiln-Sitter cone may not give the same results as found with a witness cone next to the ware.

Measuring Heat Distribution

Differences in heat distribution from top to bottom in the kiln are usually far more noticeable for cooler firings like decals. A 2 or 3 cone difference at 022 may only be a 1 cone difference at cone 6. This is because at higher temperatures radiation heats the kiln more effectively.

Slowing the first half of the firing can help heat distribution problems. This also helps by allowing more time for air to enter the kiln and burn out organics and for carbon monoxide to leave the kiln.

Use a controller to set heating rates and soaks for more precise firings.