Wood Filler Turning Black?

I’ve always made up my own wood filler with dust from a sander, glue and water. At one point, I had some filler that I had mixed up turn black. Do you have any idea what type of dust contaminated my filler? I can’t seem to pinpoint the type of wood that was being used that might have caused it.

Michael Dresdner:┬áIt’s not the wood alone, but the combination of wood and glue. Waterbased emulsion glues, like white and yellow glue, often contain a strong amine to keep them in suspension. The amine can react with any wood high in tannin and turn it dark, just as oak will turn dark if you wipe it with ammonia. I always advise using hide glue for wood filler. It will not react with any wood, is pH neutral, sands better, is reversible, does not creep, and will take water-soluble dye stains.

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