Lets talk about clay bodies and absorption + Hypothesis
We start with the knowledge that glaze truly is just minerals floating in water; A suspension. We also know that the ratio of water to glaze is important for the efficacy of the glaze and color. Because glaze is a suspension of water and minerals this means the more water you have in a glaze the less mineral (the thing that makes the actual glaze) you get when glaze a pot by comparison. 50% water and 50% minerals gets you more mineral on application than a glaze than 60% water and 40% mineral. This is one of the reasons it’s so important to track how much water you put in your glazes if you want consistency. This was a massive discovery for me as a glaze maker. You ought to keep track of your water as an ingredient. Weigh the Milliliters of water in the glazes you make and keep track of how they effect the glaze. You can do this easily with a gram scale, which you should have already as a glaze maker.
“But Donte, if the glaze itself is really just the minerals why do we need the water at all?”
In truth the water is a carrier for the minerals. When you glaze a bisque pot the water is absorbed into the pours / capillaries of the pot, leaving behind the minerals on the outer layer of the pot which later becomes glaze when heated. Keep in mind I said the water is absorbed into the pot, It doesn’t disappear. This is one of the main reasons I have problems with water soluble minerals being used in glazes. The water soluble mineral will combine with the water and move into the pours instead of staying with the glaze on the outer layer of the pot where it belongs, which ultimately ends up being stuck in the pours of the bisque causing problems and not contributing to the efficacy of the glaze as much. After the water is absorbed it will eventually evaporate or be driven off by heat. Logically this means the bisque has an absorption limit; an amount of liquid the bisque can absorb before being full or “water logged” as I like to call it. If you dunked your bisque work into water for a while it would ultimately absorb as much water as it can before the pours fill with water, making if difficult for the water to be absorbed along with any glaze it would have carried with it.
This leads me to my final point. The thickness of your clay also contributes to the amount of water it can absorb. Granted, this isn't as strong a variable as properly measuring your water when making glaze, but it merits consideration. There is an amount, and a rate at which the capillaries of your clay will absorb the water and the minerals in which is carries. I like to say pours as it is easier to translate. Recently I've gotten into spil casting. A much faster, efficient way of producing basic shapes. Many potters use this method for production work and test tiles. While you don’t have to make anything by hand, the trade off is getting a more consistent shape. Slip is put into the cast, the cast absorbs the water from the slip leaving only clay behind and, boom, you have a fast, even shape. I bring this up because a thinner product ( like the test tiles I have been making) will naturally need less clay to make than a handmade object (mine do at least). Less clay equals less pours, less pours equals less absorption / capillaries suction, less absorption means less water and minerals are being absorbed along with it, which in turn means I'm technically means I'm getting less glaze.
Let me show you one of my most reliable glazes. This is metal Garurumon.
Metal Garurumon cone 6 ox on porcelain
Bowl 1
Metal Garurumon on porcelain
Bowl #2. Same kiln different bowl.
Metal Garurumon on porcelain
Bowl #2 (back)
Metal Garurumon on red clay
Notice even on different clay its still damn near the same color.
Bowl #3
Getting a little louder
Metal Garurumon on a dragon fruit clay body with massive texture!
Same COLOR, different clay.
Almost yelling
HERE IS THE GLAZE ON A PORCELAIN CLAY BODY WITH A LOT OF TEXTURE.
Are you getting what I'm throwing down?! This Is a reliable consistent glaze on damn near everything between cone 5-7. Lets do one more.
Full on yelling now
THIS IF METAL GREYMON ON A Horizontal test TILE
Whiteness How consistent IT . IS!
Now take a look at the glaze on one of my slip cast test tiles.
Metal Garurumon on a porcelain test tile cone 6 ox.
This… keeps happening to me. I have tested about three glazes in this fashion. Reliable, good glazes that I know very well. Almost all of them come out way different on my super thin test tiles rather than and thrown product.
Which for me are much more thick.
The key here is to remember that my test tiles are about 3-4 times thinner than anything I throw; throwing off the absorption of the water and in turn of the minerals within . To be clear, I do think it would have to be a massively thinner product such as in my case. I also have no tests on super thick pieces having the opposite effect. But my current hypothesis is that if a bisque pot is very thin, it decreases the amount of absorption via how many pours the clay body has available. Knowing this I've restarted to make my tiles a bit thicker. Notice the tile on the left, how thin it is. (This is how thin I was glazing with)
P.S Keep in mind I bisque my pots between cone 09 and 08 because cone 04 (the standard for bisque in America) its’ a little too close to fully fired for me, messing up my absorption. I find I get way better results with a lower bisque temp. Every one of the pictures you see here was fired at cone 08 bisque and still this happened.
Way too thin in comparison to my handmade work.
It reminds me of the old potters that give advice. They will tell you stuff that makes no sense until you run into something like this. I once remember an older potter friend of mine telling me
“ I glaze the inside of my work, wait a few days, then glaze the outsides. The pot can only drink so much at a time”
I assume it depends on the thickness of your clay is and the absorption level of your clay. My example here was easily 4x thinner than anything else I make. A little disclaimer before we go. This has happened to me enough to confirm suspension but not enough to make it a hard fact. I need to give more proof than just 3 glazes before saying this is true true, But at the moment I have a good amount of correlation.
