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Recently, Maria saw a tongue depressor, "Ooh, a blank surface!" Here's a closer look with Zentangles, front and back:
Tongue depressors (and popsicle sticks) are usually made from birch wood. Birch is great because with its nice tight grain, your ink doesn't bleed and feather out even on unfinished wood.
(Trivia: Did you know -- one reason birch is used for tongue depressors and popsicle sticks is that it has no taste to it.)