How to make a white glaze and question your sanity
Mugs in white
When I first got my home studio settled, one of my primary goals was to develop a color palette of 3-4 base colors that I would use for the majority of my pieces. I knew out of those core colors, one of them was to be a plain, basic white.
Turns out developing a white glaze ended up being a nebulous and challenging project. I tested samples for months. Thinking that this would be easy, it turned out to be everything but. A white glaze was my white whale, I guess.
White No. 1
The first white I tried was the semi-matte base #2 recipe, highlighted in John Hesselberth and Ron Roy’s book Mastering Cone 6 Glazes. This is a pretty well known intro to making cone 6 glazes reference and for good reason. While the book itself doesn’t contain a white recipe, it mentions the different opacifiers that can be used to provide full color coverage. It mentions using rutile, zircopax1, and tin oxides to opacify glazes. Some online research led me to decide on adding 8% to the base recipe would be sufficient to make a plain white. Easy, right? I made a small test batch of 100 ml and tested it on a small tile made out of a clay body I had come to like - an ever so slightly buff colored porcelain.
To no surprise, this white was white. The zircopax was a great opacifier, but it felt…boring? It was just plain, I guess. It reminded me of a bathtub or worse, a toilet. It also clashed with the clay body itself. I didn’t feel like a cool-toned glaze matched well with the warmness of the porcelain.
In addition to that, it was a little more glossy that I’d like, even when using the suggested firing cycle the book recommended. So to my disappointment (and even though I didn’t want to admit it), I had to go back to the drawing board.
White No. 2
I figured in order to control variables in my situation I’d try to tackle the glaze texture first before addressing the color. I tried the semi-matte base #1 recipe from Mastering Cone 6 Glazes. This was also more glossy than I’d like, so I began to pivot to some recipes outside of the book, looking for ones that shared the majority of the base ingredients I had purchased to make the first few.
White No. 3 & 4
I found a couple of recipes on Digitalfire and tried G2934 and G2934Y. They were pretty similar but something about the G2934Y’s texture made me appreciate it more. Firing on the recommended slow-cool cycle really gave me what I was searching for, so I decided to go with that a the base. Now to fine-tune the color, as 8% zircopax in both of these still had the same bathtub white issue.
Base glaze with 8% zircopax is too white for the color of this clay - in my opinion!
White No. 5
I knew I couldn’t use pure zircopax in my opacifier because the white would be too jarring. And in another interesting finding, for this glaze in particular it was noted that adding too much zircopax can cause glaze crawling2 in joints and sharp angles of pieces. I did experience this with a few test mugs. So I needed to amend it with something else. I tried tin oxide, which gave a slightly warmer tone. A little cooler than I wanted, but I was moving in the right direction. The frustrating thing about tin oxide though - its expensive. Zircopax at my local retailer is $10/lb. Tin oxide is $49/lb. So not something I want to use a lot of.
White No. 6
I found out that adding rutile warmed up the glaze a lot. I tried a few test batches of G2934Y with different levels of rutile, testing its ability to opacify but also turn it straight up khaki brown.
Base glaze with 4% rutile makes for creamy sand color for this clay body. It doesn’t have enough white for what I was looking for.
I began to piece together an idea - maybe blending varying levels of zircopax and rutile would do the trick? I also tested adding a bit of a white mason stain. I’m hypothesizing that this mason stain probably has some tin oxide in it but not as much, and the price point is a lot nicer. I liked the results I was beginning to get.
So after trialing way too many of combinations, I think (???) I landed on a good combination of opacifiers to make a stain warm but not brown, but also not too stark white, that also provides full coverage. I’m calling it White No.531 - it has 5% zircopax, 3% white mason stain, and 1% rutile.
Stark white vs. warm white glazes on a buff porcelain clay body.
It wasn’t fast or easy. If I were to use any other clay body it might not be a right fit, but I love what it looks like right now.
White No.531 on a small bowl. Its not too white or too brown.
I’ve made a large 12L bucket of this glaze, and look forward to using it as the main white for things I made as well as use it as a base for other glazes. Now, to pick to some actual colors…should be easy, right?
