French Vanilla Opal (000137) has a habit of developing unexpected colors and patterns either based on its heat history during the manufacturing process, or based on contact with even small amounts of copper or silver. You won't see the aberrations in the cold sheet--these marks show up after firing.
If you don't enjoy these surprises, and you want a consistent warm white color, we suggest that you use Cream Opal (000420) or Warm White Opal (000920). These two styles are much less reactive and unpredictable than French Vanilla.
Mary Kay Nitchie
Bullseye Glass Co.
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