[Brandee Ross]

Over the weekend I completed my first oxidation firing. I've been working with clay for a few years, but have never been involved in any of the kiln work so this was a completely foreign experience.

The firing went well except for one concern: there is a light mist of black/blue specks on every kiln shelf. It almost looks like a fine sprinkling of black pepper. Is this normal? Do I need to clean these tiny dots off before another glaze firing, or can I just apply a light application of kiln wash to the shelves? The areas under the pots are free from this defect.

Edit: here's some pictures.

[Chris Campbell]

Some glazes do go airborne ... they can settle on other pots near them and on the kiln shelf.
I am not a technical whiz so cannot tell you which ingredient does this or why, but it does happen.

I usually scrub them off before I use the shelves for other pieces ... they release fairly easily if you
use kiln wash on the shelves.

[Brandee Ross]

Thanks Chris. It did land on many of the pieces, but it's only really noticeable on the white-glazed ware. I used a combination of commercial glazes and some I mixed myself (I was feeling adventurous on my debut firing). I can't tell which ones might have caused this by looking; it seems evenly distributed throughout the layers. The kiln is also vented and was thoroughly vacuumed before this firing.

Do these tiny airborne particles have any negative effect on my kiln elements?

[Katzeyes]

I found that this happened when colemanite was one of the glaze ingredients - it explodes off the surface as it suddenly expands or contracts, so I gave up using it. Yours probably isn't this ingredient as it's not widely available now. But whatever's causing it, if you do this enough times, the dots of glaze will join up and you'll have a glazed shelf that every piece will stick to during firing. Scrape off the dots, and make sure your shelves are well covered with fresh kiln wash is my advice. Good luck.

[John Britt]

Brandee Ross, on 12 April 2010 - 07:47 AM, said:

Over the weekend I completed my first oxidation firing. I've been working with clay for a few years, but have never been involved in any of the kiln work so this was a completely foreign experience.

The firing went well except for one concern: there is a light mist of black/blue specks on every kiln shelf. It almost looks like a fine sprinkling of black pepper. Is this normal? Do I need to clean these tiny dots off before another glaze firing, or can I just apply a light application of kiln wash to the shelves? The areas under the pots are free from this defect.

Edit: here's some pictures.

Was it a cobalt blue or cobalt black glaze?