Square Red & Black Porcelain Button Originally uploaded by la_v_i_k_a
Square buttons...a rarity, and often a collector's item. That's something new, that I just learned, lately. I thought it was interesting and then thought you might be interested in learning something new about bright red glazes.
In the past, red was a dangerous color: cadmium is poisonous. Its glazes could also be finicky and disappointing, burning out at the slightest overheating or affected by copper glazes fuming nearby during the firing, both resulting in a bland unattractive gray. Your work was ruined.
Now, cadmium is encapsulated in zircon (a silicate & a word we get from the Middle East) before being added to glazes. Structurally trapped within zircon and used as a stain, in suspension, rather than as a soluble oxide, it cannot leach (and soak into your dinner salad, in other words!). The result is that you can eat off of bright red dishes, as never before.*
This button combines a metal saturate glaze, on the left (most likely some combination of copper & iron, along with cobalt--It shows a bit blue when thinly applied), with a bright cadmium red. An impossible combination, just a short time ago.
*Just be careful: if you bought that bright red decorated dish abroad, in an unregulated market, it may still be unsafe.