What causes glaze to run?

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.

Why does my glaze run?

Glazes that run likely do so because they have excessively high levels of fluxing oxides. Or inadequate Al₂O₃. Both of these suggest the presence of chemical imbalances that contribute to leaching and lack of durability (just like under-firing).

Why is my glaze crawling?

Crawling. 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.

What happens if you put too much glaze?

Glaze thickness: Glaze coat too thin → ugly. Too thin and glaze can be rough and dry, ugly, and sometimes a different color. If your piece looks bad after firing, you can sometimes add more glaze and fire again.

Can you Refire Overfired glaze?

Once it has had a certain amount of heatwork, the chemical makeup of the glaze will have been altered. So, when you are refiring, you are piling a lot of heatwork onto glaze that is already almost mature. This can lead to the glaze being over mature or overfired.

Understanding Pottery Chapter 19 Glaze Defects

What happens if you underfire glaze?

Underfired glazes are usually matte and dry and can feel rough. Some gloss glazes seem like they were properly fired until you either look closely or use the object.

How do I stop my glaze from bubbling?

If necessary apply a fine particled slip to leather hard or dry ware to filter internal body gases into finer bubbles during firing. Apply the glaze in a thinner layer to minimize its ability to contain large bubbles.

Why does my glaze have pinholes?

Perhaps the most common of all glaze defects, pinholes are tiny holes in the glaze surface which penetrate all the way through to the body. They are caused by gases escaping from the clay body during the firing cycle, after originating from tiny pieces of organic matter, such as charcoal, which is present in the clay.

Can you glaze fire twice?

To summarize, it's possible to glaze fire pottery twice or even multiple times. Fired pottery can be glazed several times to add textures, accents, and effects, and multiple firings are possible.

How long does glaze need to dry before firing?

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.

Can you fix pinholes in glaze?

The Glaze Was Fired Too Quickly

If you see more pinholes in the thicker parts of your pottery pieces, you can fix the issue by firing more slowly.

How do you stop pin holes?

Pin-holes through air or solvent trapped inside the membrane

When membranes are applied which contain solvents it is important to apply thin coats to prevent the appearance of pin-holes. The reason for this is that solvents are very volatile and tend to rise once the membrane has been applied.

What is shivering in glaze?

In shivering the fired glaze is under too much compression and begins to buckle or flake off in sheets exposing the underlying clay body. If one glaze shivers adjusting the glaze with a high expansion material such as frit or feldspar will bring the glaze into a compatible fit with the clay body.

Why is my glaze cracking before firing?

When a glaze cracks as it dries on a pot, it usually means that the glaze is shrinking too much. This is normally caused by having too much plastic material (ball clay) in the glaze.

What does over fired glaze look like?

Overfiring results in glazes that begin to run. The glaze coat may be thinner at the top of the pot and thicker at the bottom. Glaze may even run off the pot and drip onto the kiln shelf or other pots. Seriously overfired pots may show ​pinholing and pitting as the glaze reaches evaporation temperature.

Can you layer glaze on top of glaze?

While applying one single glaze to a piece can be lovely, there are some effects that come only from certain glaze combinations layered on top of each other. But you should follow some simple guidelines when layering glazes to have success. Layering multiple glazes will build up increasing amounts of glaze on your pot.

Why is my kiln Underfiring?

Small or wrong cones used. Fired to the wrong cone. Firing a Vary Fire program to too low a temp for the rate of climb. TC offset adjustment needs to be set lower.

What causes shivering in pottery?

Shivering is a ceramic glaze defect that results in tiny flakes of glaze peeling off edges of ceramic ware. It happens because the thermal expansion of the body is too much higher than the glaze.

How do you fix shivering in ceramics?

In most instances, shivering can be corrected by additions of feldspar, frit or other high-expansion materials to the glaze. If the problem persists, the solution is to adjust the clay body recipe or change to another clay body altogether.

What is glaze crazing?

Crazing is one of the most common problems related to glaze defects. It appears in the glazed surface of fired ware as a network of fine hairline cracks. The initial cracks are thicker and spiral upward. These are filled in horizontally with finer cracks. Crazing is caused by the glaze being under too much tension.

How long does glaze take to cure?

No one likes to wait, but glazing putty is one of those products that requires waiting. The drying period can last from five to 15 days.

How long should a glaze sit?

In most cases, you simply apply the glaze to strands after shampooing and leave it on for anywhere between 5 to 20 minutes before rinsing.

What temperature do you fire glaze?

Stoneware glaze firings are usually around 1200°C-1300°C. At these temperatures the clay fuses and becomes strong and impervious to water. The glaze fuses with the clay, making the ware very strong.