Wednesday, December 19, 2012

Some test tiles!

            I tested four glazes in this firing: Deep Firebrick, Mottled Spice, Verte Lustre, and a zinc-free clear. I would say that all four tests were successful in that I think I now know how to use these glazes to good advantage. They do each have some quirks, though.

            The glaze above is Deep Firebrick. It is very red! On that front I am pleased. It is red on both the dark clay and the porcelain, and I actually think it looks more interesting on the dark clay. This glaze was nice to work with - it's formulated for brushing, so that's how I applied it, and it ended up with fairly even thickness despite the brushstrokes. It also seems stiff (doesn't run off the pot during firing). The one thing that I don't like is that it spits during the firing - the porcelain pendants near these tiles were spattered with tiny red dots. It looks a bit like iron spotting, and I don't think it looks bad, but I do think I'll avoid putting bare porcelain next to this glaze in the future.

            The glaze above is the Mottled Spice, that brown glaze I've mentioned a few times. Obviously it's a little runny. Other pots that were glazed with this glaze had varying degrees of success depending on how thickly the glaze was applied. Where it was thin (thinner than I would normally glaze pieces, actually) it looks amazing. Where it was thicker, it did what you see on the tiles. I did lose a serving dish to it - I'll have to chisel it off the shelf. However, the surface is so rich and lovely that I'm willing to adjust my application techniques to use it. (Do click on that second picture and see!) I have a bit of experience with runny glazes. There was a glaze at Simon's Rock - an amber celadon - that was a lovely dark honey color. I just had to use that glaze! But it would run right off the pot if it was the thickness of normal glaze, so I learned to apply it thinly and it was amazing.


            The glaze above is Verte Lustre. It is difficult to photograph, because as the name implies it is extremely shiny, and also dark colored. I do like it a lot. It has subtle variation wherever the clay underneath isn't perfectly smooth. The information that came with it says that it is dinnerware safe, but if you take a good look at that second image you'll see that it looks different at the top of the tile. That difference was in response to that part of the tile sitting in vinegar for two hours. It's probably not going to kill anybody to eat food off this glaze (how else could it have been certified dinnerware safe?), but if you put anything acidic on it, like tomatoes, or citrus fruit, or salad dressing, or any of the other myriad acidic foods out there, you will see a mark on the glaze where the food was sitting. Thus I will avoid using it on the food surfaces of my pots in the future, and any pots that have this glaze anywhere on them will come with a warning not to put anything acidic on them. I think it will make a very fine glaze for vases and dragons, however.

            This is the zinc-free clear. Why zinc free? I've read that zinc tends to inhibit color development, particularly with greens - apparently zinc and chrome don't get along, and chrome is a very common way to achieve green. The purpose of having this glaze is so that I can mix stains and oxides into it to make my own colors. I think it is a lovely clear, maybe the nicest I've ever used. It has a nice depth of surface - caused by the bubbles. The bubbles also are the cause of the milky-ness that appears when the glaze is used over red clay. I could probably make the bubbles go away with different firing procedures, but I like them there. The glaze is very stiff, and a little bit inclined to crawl (pull away from the clay). This isn't really a problem, I'll just have to get used to what makes it crawl and avoid that. It's a characteristic that many glazes have. The one issue that does bother me about this glaze is that it's a pain to apply. The materials settle out quickly. So they make a thick sediment at the bottom of the bucket, and once I've managed to stir it up, by the time the pot is ready to dip it's settled out again. There are some things I can do to help this, so I will try those for the next firing.
            Overall I'm pleased with these tests. I think these glazes have a lot of potential, and I look forward to the next glaze firing so that I can do some more work with them.
            Does anybody have ideas of different colored or textured glazes you're interested in seeing from me? I haven't shown a matte glaze here yet - I will be getting and testing one for the next firing to make a matte black. I'm open to suggestions!


  1. Any idea what causes the spitting?

  2. No, I don't know yet. I've never encountered this before, so I'll have to do a little research to find out. I was surprised it happened in a commercially formulated glaze - you'd think they'd try to avoid such an annoying fault.