Glaze and Food Safety

ARE HPG GLAZES FOOD SAFE?

The answer is a qualified yes. HPG glazes are formulated to be as safe as possible. However, like all forms of glass, glazes gradually break down, especially when in prolonged contact with acidic or basic (alkaline) substance. Glaze chemicals are also at greater risk of leaching if not mixed or fired properly. A poorly mixed or fired glaze may have a dry or rough surface or appear more matte than expected. A glaze that crazes is less food safe because the cracks can harbor bacteria, and may also indicate a poor balance of ingredients and increased risk of leaching.

If a glaze leaches, the ingredients of greatest concern at HPG would be metals such as copper, manganese, strontium, chrome, cobalt and lithium (ingredients that give green, blue, black and red color). No lead or barium is used at HPG. Iron and other ingredients used at HPG are considered generally safe (but protect yourself from inhalation).

To Maximize Glaze Food Safety:

  • -  Mix the glaze well, all the way to the bottom, before applying to your piece.

  • -  Consider the most food safe glazes for food contact surfaces, e.g., the inside of bowls and

    mugs. (The most food safe HPG glazes are listed below.)

  • -  If a finished piece feels or looks rough or dry, don’t use it for food.

  • -  If in doubt, test your piece by applying a lemon slice or vinegar for a day or two and check for

    color or texture change.

  • -  If making a new batch of glaze, make a test tile before putting the glaze into circulation.

The Most Food Safe HPG Glazes:

Acero

Amber Gong

Antique Celadon

Butter Yellow

Cecil’s Red

Chun
Glossy White Janet’s Clear Mackenzie Celadon Majolica Creamy

Majolica White Nelson’s Clear Stone-Ware Yellow Tenmoku

U.H. Blue

Winokur Yellow Yo Thom

Potentially Less Food Safe HPG Glazes: most black, green, blue and red glazes. Consider using these

more on the outside of bowls or mugs if they will be exposed to acidic foods or beverages.

The Least Food Safe HPG Glazes: colorful glazes with dry-matte finish, e.g. Joe’s Green, Turquoise Matte, and Jack Troy (Green-Blue-Black).

Other Glaze Safety Tips:

  • -  Wear a good mask when handling dry ingredients, or if in the vicinity of the spray booth. Inhaling any dry ingredient is unsafe.

  • -  Wear gloves or wash hands after handling Chromium, Copper, Cobalt, Lithium, Petalite, Manganese, Spodumine or other potentially harmful ingredients.

  • -  Wipe up spilled glaze or glaze ingredients. Spills can become airborne as they dry.

Prepared by Scott Carter, Glaze Chair, March 2016

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