Alas, we know of the splotches in some French Vanilla sheets. We did extensive research on this glass for a customer who was using cases of it for a production line. It sometimes opalizes smoothly to a continuous color, but sometimes in areas it develops a marbled, slightly darker pattern. Our customer wanted us to either make that splotchiness go across the whole sheet, or have it disappear completely.
What we learned in our testing was this: we can't tell from the appearance of the cold sheet where/if the marbling is going to happen. We took whole sheets of French Vanilla, perfectly uniform in appearance, sliced them into 6 pieces and fired them, then rearranged them back into a whole sheet. Most of the sheet ended up smooth, but marbling happened in areas we could not predict. We also took sheets where the color was not uniform in the cold sheet, but when we fired the sheet, the color struck to a uniform, smooth French Vanilla.
Believe me, we understood the customer's need for a perfectly uniform French Vanilla, but we could not formulate it, and keep all the other characteristics the same. And we can't tell which sheets are going to behave uniformly, even by looking at them. French Vanilla is a beautiful, fickle, surprising glass. People usually don't notice the marbling if they are using it in fairly small pieces or on edge, but when used in a wide section, they are sometimes surprised by this characteristic.
Regarding the lack of reaction, I am not sure this is caused by the same phenomenon. In fact, I don't have personal experience working with a reaction between Dense White (still discontinued) and French Vanilla, but maybe other people have advice.
Mary Kay Nitchie
Bullseye Glass Co.
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