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2023 Daily updates May

Part 1 Testing a New Glaze Combination:

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! 😀

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