Glaze Pinholes, Orange Peel, Pinning
Glaze Surface Defects
If your fired item looks like it has dimples or holes in the glaze surface after firing (often described as pinholes, orange peel effect, dimples, bubbles/bubbly glaze) then the cause is gas bubbles in the glaze. These defects show up as a soft grainy or bubbled surface on the ware and appear after the glaze firing or decorating firing.
Please note that pinholes result in tiny craters with soft edges; blisters result in slightly larger craters with sharp edges. Go to our blisters article if you believe you may have this issue.
- Ensure that the wares are fully dry before firing (not damp or wet).
- Ensure that the glaze (coloured or clear) and the underglaze applications are not too thick or a combination of both. Check the viscosity of your glaze is correct and make sure that glazes are mixed thoroughly before application. If the glaze layer is too thick the gases don't pass through when the glaze is bubbling during the firing and before the glaze smoothes out.
- Make sure the glazes are not contaminated.
- Ensure the kiln is well ventilated and clean. Do not over pack the kiln and ensure there is good ventilation around each piece or shelf layer.
- Check that you have not under fired or over fired wares (cones will help determine whether the kiln is firing correctly)
- Ensure that the bisque has been fired to a minimum firing temperature of 1000°c.
- Try slowing down the firing cycle or increasing the soak period.
- Dust on bisque may also cause a problem. Ensure items are clean (customer's can be encouraged to wipe down the bisque with a damp sponge prior to decorating).
Orton Ceramics have produced a useful "glaze defects" information document - click here to read.