Ordinary starch will yield a blue colour with iodine.
The best iodine indicator (other commercial material like Vitex etc) can be made by dissolving 5 g of soluble astarch in 100 mls of boiling water. Mix raidly to dissolve. Make up to one litre with good quality water. Add one pellet of NaOH or KOH and add a few drops of 0.1% phenolphthalien indicator. When the colour disappears, discard it and make up fresh.
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