This article focuses on the process of adjusting a new pottery glaze combination and conducting tests using test tiles
Part A: Adjusting Specific Gravity
To begin, let’s aim for a specific gravity of approximately 1.46 for our Tenmoku pottery Glaze, currently, the specific gravity of this glaze stands at 1.52
To rectify this, we will add water to the glaze batch. It’s important to thoroughly mix the contents and periodically test the specific gravity as water is added
Here’s how
Step 1
Place an empty graduated cylinder on a scale and zero the scale
Step 2
Pour 350 ml of glaze into the cylinder and record the weight
Step 3
Divide that weight by 350 ml, and the resulting figure represents the specific gravity of the glaze
For example, if the glaze weighs 513 grams, dividing it by 350 ml would yield a specific gravity of 1.465
Part B: Dip Testing and Clay Bodies
Dip testing involves immersing test tiles into the pottery glaze to assess its color, texture, and interaction with different clay bodies. Each clay body possesses unique characteristics and chemistries that can influence the glaze in distinct ways. Matching the appropriate clay body to the right glaze offers numerous advantages, including the prevention of crazing (thermal expansion issues)
To conduct dip tests, gather the following materials: bisque test tiles, the glaze batch you want to test, and a small plastic cup
Step 1
Pour the glaze into the plastic cup and have your test tiles ready
Step 2
Dip the tile only three-fourths of the way down, allowing some room for the glaze to run
Step 3
If you’re testing a glaze that tends to be runny, ensure the kiln shelf is protected with a saucer or glaze catcher
In Part 2, we will explore testing the pottery overlay glaze in conjunction with this new combination. We will discuss phase separation (also known as variegation or break out glazes) and examine the effects, or lack thereof, on glaze chemistry when layering glazes
Happy potting to you! 😀
