Talcum powder is hydrophobic, meaning it doesn't mix with water. That's why they used it with the Rainbow, to try to make the Rainbow look bad in terms of filtration. I had that same exact model Rainbow and it had no problem catching dust.
the rainbow couldnt stand up to the milk test, i simply asked for a glass of milk, help it up to the rainbows exhaust and watched the milks surface turn black, not what you were told would happen when you used your brand new rainbow air purification unit, which of course was the only true selling point!
