All Glossary

Spray Glazing

In ceramic industry glazes are often sprayed, especially in sanitary ware. The technique is important.

Key phrases linking here: spraying glazes, spray glazing - Learn more

Details

In the production of smaller bisque fired ceramics it is almost always possible to dip-glaze ware. However, this is seldom an option for single-fire ware (especially if large). This is the case in the sanitary ware industry, for example. Spraying is the only option, and it is a very effective one if done properly. Typically, opacified glossy glazes of high specific gravity (up to 1.8) are employed, the low water content speeds drying (thixotropy is not generally a concern, low water content is the main issue). Potters are much more flexible and less demanding when spraying. They typically spray a water-thinned slurry on porous bisque ware that is very forgiving of runs and drips.

For best results in pottery and hobby:

-Glazes need enough clay to suspend and harden them, but not so much that they dry too slowly or shrink too much (thereby cracking or flaking off). 10-20% should be OK.
-Gravity-feed guns are the most trouble-free.
-Use a sticky kaolin as the clay portion (e.g. Grolleg, NZK).
-For lower specific gravity glazes, adjust the slurry so that it is thixotropic, that is, so it stays in suspension in the sprayer.
-Use glazes high in frit and low in troublesome raw materials (ones that affect slurry viscosity or thixotropy, are soluble and crystallize in the slurry, create a precipitate scum inside containers or ones that contain excessive particulates).
-Use the right frits. They need to source the needed fluxing oxides and complement the recipe to optimize clay percentages. For example, if a glaze needs more clay then the frits employed should have lower Al₂O₃ content so that can be sourced from a kaolin instead (or vice versa).
-Ball mill your glazes or sieve them enough to be sure there is no particulate matter.
-Spray ware when it is sill warm or even hot to encourage fast drying.
-Make sure ware is thick enough so it can absorb plenty of water.
-Make sure your spray operator is skilled and has good equipment. Spray an even layer. Start at the bottom and work upward. Be careful about over-spraying already-dry areas, if done excessively this can rewet them and cause lifting during drying (and crawling during firing).
-Spray the ware on a rotating turn-table having a knobby or spiked rubber or plastic mat on which to set the item.
-Use a good quality stainless steel agitated pressure pot sprayer.
-Apply the thinnest possible layer needed to get the desired fired effect.
-Incorporate CMC gum, if needed, to improve bonding to bisque, dry hardening and smooth out.

Again, the rheology of your slurry is important for quality, efficiency and avoidance of production issues. Experiment as needed. Document the slurry preparation, measurement and maintenance procedures well.

For good spraying technique watch the video provided below. It was graciously given to us from http://shower-shelf.com. They also document their vibratory glaze sieve on youtube (links below for it and where to get the vibration motor).

Related Information

Spray glazing a nitch shelf at shower-shelf.com

Notice he starts from the bottom and works his way upward.

Spray glazed large bowl with two glazes meeting-at-the-rim

This picture has its own page with more detail, click here to see it.

The inside glaze is G2571A, outside is the bamboo version of the same recipe (with added Zircopax and rutile). Clay: Plainsman H443. Firing: Cone 10R. No wax was needed for application yet the two colors meet at the rim in a straight line (the outside was sprayed last). We used a gravity-feed sprayer, 100ml of glaze was applied on both the inside and outside.

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