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Crawling is caused by a high index of surface tension in the melting glaze. It is triggered by adhesion problems, often caused by bad application. It occurs where a glaze is excessively powdery and does not fully adhere to the surface of the clay.
How do I stop my glaze from crawling?
Consider pouring a thin glaze slurry into the mold of a just-drained piece (perhaps a minute or two after the mold has been drained) and immediately pouring it out again. This base layer can be fired on in the bisque. It might be enough to prevent crawling when the piece is glazed later.
What is crawling in glaze?
Crawling is where the molten glaze withdraws into ‘islands’ leaving bare clay patches. The edges of the islands are thickened and smoothly rounded. The problem is by far most prevalent where bisque-applied glazes contain excessive plastic clay content or are applied thickly or in multiple layers.
Why can’t you put the glaze on the bottom of your pottery?
If you get glaze on the bottom of your pots and fire them they will stick to the kiln shelf which could result in a lot of damage to your shelf and will ruin the pot you just spent a lot of time on. The wax would stick to the bisque ware and where ever wax was, glaze would not stick.
What happens if you apply too much glaze?
Glazes having a thermal expansion lower than the body, and thickly applied on the inside of vessels, can fracture the piece during kiln cooling. Those having a higher expansion than the body will often craze if applied too thick. Transparent colored glazes will fire the wrong shade if not the right thickness.
What does bone ash do in a glaze?
When added to a clay body such as bone china, bone ash lowers the maturing temperature and adds translucency. Bone ash may also be used to give texture in low fire glazes. In low-fire glazes, bone ash acts as an opacifier, while in high-fire glazes it can create translucence.
Should you wet Bisqueware before glazing?
Use a damp sponge to clean off bisqueware before glazing. For two different glaze coats, let the first coat get mostly dry (dry to the touch, but not ‘bone dry’) then add the next coat.
How do you get glaze off?
Removing the glaze can be done by sanding the surface of the ceramic product. This process is usually done to prepare a glazed tile surface before it is painted. However, the glaze on other ceramic products can also be removed by sanding the surface by hand.
Why does my glaze bubble?
All clays release gases from burning of carbon material and decomposition of other compounds. Some clays release sulphur compounds also. If the glaze is melting during release of these gases, they must bubble up through it.
How many coats of glaze do you need and why?
Typically, three coats are applied. Each dries slowly, hardening as it does so (the glazes contain binders). This provides a stable base for the next one.
Does glaze need to dry between coats?
I brush, and I usually wait 30 minutes between coats. You can see the difference in color in most glazes between 10 minutes and 30 minutes. I have waited 24 hours before applying a second coat, and I notice no difference. This however changes the more coats you add the more time you need to wait between coats.
Can I Refire a glazed piece?
Since these firings need a lack of oxygen in order for the glazes to develop, you can’t refire them in an oxidation firing (electric kiln) or all the reduction you did will be reversed. Reduction and Raku glazes may or may not look good re-fired in oxidation, but they will probably look different.
Can you glaze fire twice?
Pottery can be reglazed and refried multiple times. Most pottery glazes need to be applied in 1-3 layers. Pottery that has already been fired with a glaze can be re-glazed and fired 2 times.
How soon can you fire after glazing?
Some potters will put their glazed ware straight into the kiln and fire it immediately. However, glaze contains water, and this is absorbed by bisque ware when glaze is applied. Ideally, leave your pottery overnight after glazing to allow this water to evaporate. Or add a pre-heat to your firing schedule.
What does over fired glaze look like?
This is a translucent frit-fluxed porcelain that demands accurate firing, the over fire has produced tiny bubbles and surface dimples in the glaze. The mug rim has also warped to oval shape. If it fires too hot like this, then program to fire to cone 5 with a longer soak, or cone 5.5 (if possible).
What happens if glaze is Underfired?
If your pottery is significantly underfired, you can fire to the original target temperature. However, if your glaze is almost but not quite mature, then refire to a lower target temperature. For example, if your original target temperature was cone 6, you may have success refiring to cone 5.
Can you put underglaze on top of glaze?
Underglaze can be used on greenware, on bisque, or on top of glaze. When and where it’s used is dependent on how you want your finished piece to look. Underglaze on top of glaze is traditionally used for majolica pieces. We always recommend you learn about and test your products.
What happens when you use too much glaze?
Applying glaze too thinly can result in rough glazes and can affect the glaze’s color. Applying glaze too thickly can cause the glaze to run off the pot, weld lids to pots and pots to kiln shelves, and can result in blistering. Applying glaze unevenly may result in splotches and streaking in both color and texture.
How do you fix a crazing glaze?
If you do want crazing to happen, try lowering the firing temperature. Avoid adding extra silica or sand to the clay body. Conversely, ways to correct crazing include changing to a different clay body which better fits the glaze, adding silica to the existing clay body or increasing the firing temperature.
