The perfect storm I seem to have created appears to go like this:
1. Because I failed to notice a 500G counterweight on the far side of my Ohaus scale several years ago, I put WAY too much of something in that glaze. Fortunately, I noticed the weight as I was setting the scale for the next chemical (I always mix 10,000G batches -- 4-6 batches at a time in paper bags, so that I only have to go out to my barn to get another pre-measured, but unmixed batch when I run out). Anyway, it resulted in such huge batches, that it's been years since I've mixed this glaze. That made me more uncertain about how different ALL the chemicals might be from the last time I mixed this glaze.
2. Since zircopax is expensive too, and I just happened to be virtually out of it, I decided that since I had quite a bit of tin on hand, I'd half-and-half it. Now, Ken Ferguson's original glaze didn't have zircopax at all, but I'd learned over the years that, for my purposes anyway, the substitution didn't make any difference.
3. I've been using two clays in my studio for about four years now. One of them is Laguna's B-mix which is quite possibly the least consistent commercial clay I've ever used. (if I had the patience for wadding and the like, I'd probably
switch to one of those new super-silica porcelains like Turner's or Coleman's). This only matters because, in order to keep the B-mix from gassing out and giving me surface bubbles, I've been bisquing higher. Even that would be okay (sort of) except that I bisque in a gas kiln and have a half to a full cone's difference at bisque temp. That means that the stoneware on which I was putting that glaze was bisqued higher than necessary. I even found a piece that was bisqued lower and the glaze (though somewhat thinned) didn't curl off.
4. The bisque ware has been accumulating out in my barn over the winter. So it was quite possibly a bit cold and damp (one of the lesser possibilities on the list)
5. The batch of glaze was over half new glaze. That means that it had only sat overnight in the vat. That means that its particle size hadn't deteriorated from sitting in water for a long period of time -- hadn't "aged".
6. The perennial problem I face with that glaze -- no hydometer can measure it as thin as I like it (they sink below the surface when the glaze is right). At one time I tried to make a hydrometer specifically for that glaze. I maytry that again.
The fix I'm trying right now (I won't know until I open the kiln tomorrow) is to single dip the glaze and then spray the areas that I wanted better coverage. At least doing it that way, the glaze stayed on. My fingers are crossed as I'm typing this. That's made for lots of typographical errors, but when you're superstitious, what else you gonna do?
1. Because I failed to notice a 500G counterweight on the far side of my Ohaus scale several years ago, I put WAY too much of something in that glaze. Fortunately, I noticed the weight as I was setting the scale for the next chemical (I always mix 10,000G batches -- 4-6 batches at a time in paper bags, so that I only have to go out to my barn to get another pre-measured, but unmixed batch when I run out). Anyway, it resulted in such huge batches, that it's been years since I've mixed this glaze. That made me more uncertain about how different ALL the chemicals might be from the last time I mixed this glaze.
2. Since zircopax is expensive too, and I just happened to be virtually out of it, I decided that since I had quite a bit of tin on hand, I'd half-and-half it. Now, Ken Ferguson's original glaze didn't have zircopax at all, but I'd learned over the years that, for my purposes anyway, the substitution didn't make any difference.
3. I've been using two clays in my studio for about four years now. One of them is Laguna's B-mix which is quite possibly the least consistent commercial clay I've ever used. (if I had the patience for wadding and the like, I'd probably
switch to one of those new super-silica porcelains like Turner's or Coleman's). This only matters because, in order to keep the B-mix from gassing out and giving me surface bubbles, I've been bisquing higher. Even that would be okay (sort of) except that I bisque in a gas kiln and have a half to a full cone's difference at bisque temp. That means that the stoneware on which I was putting that glaze was bisqued higher than necessary. I even found a piece that was bisqued lower and the glaze (though somewhat thinned) didn't curl off.
4. The bisque ware has been accumulating out in my barn over the winter. So it was quite possibly a bit cold and damp (one of the lesser possibilities on the list)
5. The batch of glaze was over half new glaze. That means that it had only sat overnight in the vat. That means that its particle size hadn't deteriorated from sitting in water for a long period of time -- hadn't "aged".
6. The perennial problem I face with that glaze -- no hydometer can measure it as thin as I like it (they sink below the surface when the glaze is right). At one time I tried to make a hydrometer specifically for that glaze. I maytry that again.
The fix I'm trying right now (I won't know until I open the kiln tomorrow) is to single dip the glaze and then spray the areas that I wanted better coverage. At least doing it that way, the glaze stayed on. My fingers are crossed as I'm typing this. That's made for lots of typographical errors, but when you're superstitious, what else you gonna do?
My friend potter, now deceased, gave me a gallon of glaze marked Ferguson Green cone 10.
ReplyDeleteI am almost at the end of the container and have no formula. Is the glaze you referred to in your blog this glaze? I would appreciate the recipe.
Enjoyed your blog about the art show, the oil painter, and the ram press production