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MGBase1 - High Calcium Semimatte 1 (Mastering Glazes)

Modified: 2025-12-30 03:49:26

From page 86 of Mastering Glazes book

Notes

While "Waterfall Brown" is about movement and "Waxwing Brown" is about a waxy feel, HCSM 1 is all about the classic, soft, "eggshell" finish that defines the authors' approach to functional matte glazes.

Key Properties
• Visual Appearance: A smooth, buttery, semi-matte surface. It is naturally a soft off-white or cream color in its base form. It does not have the "dry" look of an underfired glaze; instead, it looks like a fully melted glass that has simply been "dulled" by microscopic crystals.
• The Science: The matteness comes from Calcium-Silicate crystals (Wollastonite) that grow as the glaze cools. For this reason, the authors highly recommend a controlled cooling cycle ("down-firing") to give these crystals time to form.
• Surface: Extremely smooth to the touch. It is often described as having an "oily" or "buttery" feel rather than a chalky one.
• Durability: Hesselberth and Roy designed it specifically to avoid the common "matte glaze traps"—leaching and staining—making it safe for food surfaces.

Likes (Pros)
• The "Feel": This glaze is a favorite for functional potters because of its tactile quality. It is pleasant to hold, which is vital for mugs and cereal bowls.
• Reliable Color Canvas: It acts as a "blank slate." Because it is a high-calcium base, it accepts colorants like Cobalt (blue), Chrome (green), or Manganese (purple) with great clarity and soft, variegated transitions.
• No Running: It is a "stiff" melt. It stays where you brush or dip it, allowing for clean lines between different glaze colors.
• Resistant to Staining: Unlike many matte glazes that absorb coffee or beet juice stains over time, the tight crystalline structure of HCSM 1 makes it easy to clean.

Dislikes (Cons)
• Cooling Sensitivity: If your kiln "crash cools" (cools too fast), this glaze can come out looking glossy rather than matte. You must be willing to program your kiln to slow down between 1900^circ F and 1500^circ F.
• Cutlery Marking: Because the surface is composed of tiny crystals, it can sometimes act like very fine sandpaper against metal. Over time, some users find that stainless steel forks leave grey "pencil marks" on the surface (though HCSM 1 is much better in this regard than most other mattes).
• Application Thickness: If applied too thick, it can occasionally "crackle" or crawl in corners. If too thin, it loses its buttery feel and can look a bit "stony" or dry.
• Variegated Slate Blue Variation: One of the most famous variations of this base (Variegated Slate Blue) is notoriously picky about the specific batch of Red Iron Oxide and Rutile used; small changes in minerals can shift it from a beautiful blue-grey to a muddy brown.

Related Information

Links

XML to Paste Into Insight-live

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