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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

Tap picture for full size and resolution

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.

Links

URLs http://www.finishsystems.com/catpressurepots.html
CA Tech Paint Pressure Pots for Spray Glazing
URLs https://www.youtube.com/watch?v=0zXfghDNxUg
ShowerShelf.com vibratory screen that fits the top of a five-gallon bucket
URLs https://www.amazon.com/Vibration-3600RPM-Industrial-Asynchronous-Vibrator/dp/B07P5CLJLP/ref=sr_1_12?qid=1559306388
Industrial vibration motor at Amazon.com
URLs https://www.luepottery.hwy.com.au/PDF/glaze%20spray.pdf
Glaze Spraying booklet by Roger Graham - Excellent reference
URLs https://www.smac.it/en/dettaglio.php?idprod=239
K-Flow automatic glaze flow rate controller for spray nozzles
URLs https://www.smac.it/en/dettaglio.php?idprod=232
Versatile/Plus airless tile spraying machine
URLs https://www.smac.it/en/dettaglio.php?idprod=45
Airless pumps for glaze and engobe suspensions
URLs https://www.smac.it/en/dettaglio.php?idprod=29
Multicolor four color spray gun
Glossary Specific gravity
In ceramics, the specific gravity of slurries tells us their water-to-solids ratio. That ratio is a key indicator of performance and enabler of consistency.
Glossary Viscosity
In ceramic slurries (especially casting slips, but also glazes) the degree of fluidity of the suspension is important to its performance.
Glossary Deflocculation
Deflocculation is the magic behind the ceramic casting process, it enables slurries having impossibly low water contents and ware having amazingly low drying shrinkage
Glossary Once fire glazing
Refers to the practice of firing ceramics in one firing (rather than two) to produce a fully glazed product. This practice requires more technical expertise.
Glossary Dipping Glaze
In traditional ceramics and pottery dipping glazes can be of two main types: For single layer and for application of other layers overtop. Understanding the difference is important.
Glossary Base-Coat Dipping Glaze
These are ceramic glazes intended for dipping but which contain a gum to enable them to adhere to the body better and tolerate over-layers without danger of flaking or cracking.
Glossary Brushing Glaze
Hobbyists and increasing numbers of potters use commercial paint-on glazes. It's convenient, there are lots of visual effects. There are also issues compared to dipping glazes. You can also make your own.
By Tony Hansen
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