Did a little bit of experimenting today. Got some Iodophor (Betadine) from work. Took a sample of wort from mash very early to ensure there would be starch.
Poured a small amount into a white saucer and added iodophor/betadine - NOTHING!
Unless this stuff goes bad from sitting in a hot garage, it simply doesn't work as a starch indicator.
Used the old bottle of iodine that also sits in that garage and is about 5-6 years old, and guess what, it turns very subtly blue. I think, esp in darker wort, that dilution of the wort with water will help to notice the change in color. as well as use of a white plate/saucer.
I'm looking for some "fresh" iodine now but apparently its hard to find!
Also curious about thermometer calibration. I'm getting very different reads on the PID/Temp controller than the built in thermometer on the Mash tun, a standard "lab" thermometer is closer to the PID readout and so is a digital thermometer I've got.
I think the built in blichman thermometer is off by several degrees.