I’ve been testing AMACO Underglaze Chalk Crayons on different clay bodies, and the biggest takeaway so far is simple: the clay underneath changes the result dramatically.
On dark clay, some colors stay surprisingly visible, some become much more muted, and others almost disappear.
For this test, I used black stoneware and red stoneware.
White underglaze crayon on red stoneware
White over red stoneware creates a much softer effect than I expected.
The white is still visible, but it doesn’t stay bright or sharply defined. Instead, it fades slightly into the clay and creates a softer, almost chalky line.
I tested this combination without glaze, and I like the result.
It doesn’t have the strong contrast you might expect from white over a dark clay body, but the softer effect feels very natural and integrated into the surface.
Result: visible, soft and slightly muted.
Clay used: 547 Red Sculpture Clay from Standard Clay
Testing underglaze crayon colors on black stoneware
Black stoneware was the more interesting test because the clay affected every color differently.
Some colors held up much better than others.
The colors that worked best were:
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Yellow
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Green
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Light blue
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Blue
They all became more muted compared with how they looked before firing, but there was still enough contrast for the marks to remain clearly visible.
Yellow worked especially well against the black stoneware.
Clay used: 266G Umbria w/ Grog from Standard Clay
Which colors faded on black clay?
Pinks and purples were much less successful.
They lost a lot of their brightness and became difficult to distinguish from the clay body.
Grey also faded considerably.
Overall, nearly every color looked more muted on black stoneware, but blues, greens and yellow retained enough intensity to still work well.
If you want a strong, graphic result on black clay, I would start with those colors.
White crayon on black stoneware
White was the most surprising test.
Without glaze, the white crayon is visible, but the line is softer and blurrier than I expected. Instead of a crisp white drawing, it creates more of a smoky grey-white mark.
Then I tested the same white crayon under clear glaze. The white essentially disappeared.
The glaze made the already-muted marks blend almost completely into the black clay.
I really liked the appearance of the black clay fired at cone 06. At this temperature, the clay took on a soft terracotta tone that paired beautifully with the white drawing.
There is a drawback, though. At cone 06, the white crayon does not permanently set into the clay and can still smudge or rub off by hand.
Firing the same black stoneware to cone 6 solves that problem, but it also creates a significant color shift in both the clay and the drawing. So there is a tradeoff between the softer low-fire appearance and a more durable, fully fired surface.
If you are planning to use white underglaze crayon on black stoneware, I would definitely test your exact clay, firing temperature and glaze combination first.
Cone 06, unglazed: soft terracotta clay with a beautiful white drawing, but the crayon can still rub off.
Cone 6, unglazed: more durable, but with a significant color shift.
Cone 6 with clear glaze: the white almost completely disappears.
What worked best?
From these tests, my favorite combinations were yellow, green and blue over black stoneware, and white over red stoneware when I wanted something softer and less graphic.
The main thing I learned is that underglaze crayons don’t behave like an opaque layer sitting on top of the clay.
The color of the clay body becomes part of the final result.
On black stoneware especially, some colors have enough intensity to remain visible while others visually disappear into the darker surface. Firing temperature and glaze can change the result again.
Always test the clay and glaze together
These are my results with the specific clay bodies, crayons, firing schedule and glaze I used.
A different black stoneware, red clay or clear glaze may produce a different result.
That’s why I always recommend making a small test before using a combination on a finished piece.
A quick test tile can tell you much more than a color chart when you’re combining a specific clay body, surface material and glaze.
Next, I’ll share how these same AMACO Underglaze Chalk Crayons perform on white porcelain and white stoneware, where the colors pop much more vibrantly.
If you want to try these surface experiments on your own slab-built forms, you can explore my collection of pottery templates at From Fran. They’re designed and tested in my studio so you can build the form first, then experiment with clay bodies, drawing, color and glaze on top.
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