Midfire Hiiro

This is a series of related clay bodies for cone 6 firing.

• Targeting a Silica-Alumina Ratio of 3.0 for Hiiro flashing
  • This is primarily for interacting with Shino Glazes.
  • Should also flash well in Soda Firing
  • May also be a candidate for Hidasuki
• Higher concentration of "impurities" like iron specks and coarser particles
  • This is for stronger surface texture which will interact with glazes

Hiiro 1

Cone 6 clay body designed for Alkali Flashing. Targeting a Silica-Alumina Ratio of 3.0 and 1-2% Fe2O3. I'm using it for more intense colors with Shino Glazes, but it should also function well in Soda Firing. Inclusion and ratio of Goldart and Hawthorne Bond is for adding some iron speckling.

Throws decently well. Not quite as plastic as Laguna's clays, but perfectly fine for throwing functional tableware. Tends to buckle a little when throwing narrower cylinders. Some 3% grog may be useful to increase clay strength.

Even though Hawthorne and Helmer bring coarser particles, they are undetectable during throwing and trimming. Trimmed pieces are automatically burnished to a waxy finish by steel trimming tools. To preserve some of the coarser texture, avoid using ribs or trimming.

After a week in water, the pH remained neutral. At least in short time frames, the neph sye does not release alkali metal ions (which would decrease plasticity).

Hiiro 1 with light grog

The 3% added grog really improves throwing properties. I don't think I can throw any taller, but when I do, the clay has less of a tendency to twist or collapse.

I think 48 mesh is a little too small. Since I'm mainly using the grog for texture (if I really wanted more plasticity I could just add more bentonite), I think replacing the kyanite with ~30 mesh grog would look better without feeling too sandy. I've tried 3% Mulcoa Grog 47-20x50 in my Atmospheric Body 3, but the graininess is too intense, especially during trimming.

The foot after trimming. There are some light "fuzzy" textures, similar to Japanese Mogusa Clay. I think Mogusa has a large amount of particles in the 40-50 mesh range. The foot needs to be a little softer than leather hard for this texture to occur; this only happens when the clay is torn rather than cut.

Hiiro 2

• Replace bentonite and Helmer with Tennessee 10
  • The flashing color of Helmer and Tennessee 10 are similar
  • I prefer plasticity of a ball clay over kaolin + bentonite
• Decreased neph sye content
  • Neph sye in excess of what's needed for maturity
  • Tennessee 10 is less refractory than kaolin
    • Figured this out when firing Atmospheric Body 2 at cone 6 for glaze testing
• Increased Hawthorne
  • Because I feel like it

Created 2023-12-05. Updated 2024-03-11.

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